Seven-Octave High-Brightness and Carrier Envelope Phase-Stable Light Source - Elu, Ugaitz; Maidment, Luke; Vamos, Lenard; Tani, Francesco; Novoa, David; Frosz, Michael H.; Badikov, Valeriy; Badikov, Dmitrii; Petrov, Valentin; Russell, Philip St. John; Biegert, Jens (2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings, 2021)
We present a carrier-envelope-phase stable light source with simultaneous spectral coverage across 7 optical octaves (UV to THz) by combining soliton self-compression, dispersive wave generation and intra-pulse difference frequency generation.
CRIS-Team Scopus Importer:2021-12-24

Seven-octave ultra-bright pulse generation - Enders, Michael T.; Elu, Ugaitz; Maidment, Luke; Vamos, Lenard; Tani, Francesco; Novoa, David; Frosz, Michael H.; Badikov, Valeriy; Badikov, Dimitrii; Petrov, Valentin; Russell, Philip St. John; Biegert, Jens (Optics InfoBase Conference Papers, 2021)
We present an ultra-bright carrier-envelope-phase-stable light source spanning seven octaves (340 nm to 40 000 nm) simultaneously by combining soliton self-compression, dispersive wave generation, and intra-pulse difference frequency generation in a newly-developed nonlinear crystal.
CRIS-Team Scopus Importer:2021-12-03

Shaping Field Gradients for Nanolocalization - Nechayev, Sergey; Eismann, Jörg; Neugebauer, Martin; Banzer, Peter (ACS Photonics, 2020)
Deep subwavelength localization and displacement sensing of optical nanoantennas have emerged as extensively pursued objectives in nanometrology, where focused beams serve as high-precision optical rulers while the scattered light provides an optical readout. Here, we show that in these schemes using an optical excitation as a position gauge implies that the sensitivity to displacements of a nanoantenna depends on the spatial gradients of the excitation field. Specifically, we explore one of such novel localization schemes based on the appearance of transversely spinning fields in strongly confined optical beams, resulting in far-field segmentation of left- and right-hand circular polarizations of the scattered light, an effect known as the giant spin-Hall effect of light. We construct vector beams with an augmented transverse spin density gradient in the focal plane and experimentally confirm enhanced sensitivity of the far-field spin segmentation to lateral displacements of an electric-dipole nanoantenna. We conclude that sculpturing of electromagnetic field gradients and intelligent design of scatterers pave the way toward further improvements in displacement sensitivity.
CRIS-Team Scopus Importer:2020-04-14
Keywords: displacement sensing; localization; nanoantennas; tight focusing; transverse spin

Sharper Focus for a radially polarized light beam - Leuchs, Gerd; et al. (Physical Review Letters, 2003)
The influence of polarization on the shape of the focal spot was discussed. The focal intensity distribution for radially and azimuthally polarized input fields was compared to analyze the effect of vector properties of light. A radially polarization field led to a longitudinal electric field component for strong focusing. The results show that the radially polarized light beam was focused to a spot size significantly smaller than for linear polarization.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.sharpe

Shifting the phase of a coherent beam with a 174Yb+ ion: influence of the scattering cross section - Fischer, Martin; Srivathsan, Bharath; Alber, Lucas; Weber, Markus; Sondermann, Markus; Leuchs, Gerd (Applied Physics B-Lasers and Optics, 2017)
We discuss and measure the phase shift imposed onto a radially polarized light beam when focusing it onto an Yb ion. In the derivation of the expected phase shifts, we include the properties of the involved atomic levels. Furthermore, we emphasize the importance of the scattering cross section and its relation to the efficiency for coupling the focused light to an atom. The phase shifts found in the experiment are compatible with the expected ones when accounting for known deficiencies of the focusing optics and the motion of the trapped ion at the Doppler limit of laser cooling (Hänsch and Schawlow in Opt Commun 13:68–69, 1975).

Significant performance enhancement of InGaN/GaN nanorod LEDs with multi-layer graphene transparent electrodes by alumina surface passivation - Latzel, Michael; Buettner, P.; Sarau, George; Hoeflich, K.; Heilmann, M.; Chen, Weijian; Wen, X.; Conibeer, Gavin; Christiansen, S. H. (Nanotechnology, 2017)
Nanotextured surfaces provide an ideal platform for efficiently capturing and emitting light. However, the increased surface area in combination with surface defects induced by nanostructuring e.g. using reactive ion etching (RIE) negatively affects the device's active region and, thus, drastically decreases device performance. In this work, the influence of structural defects and surface states on the optical and electrical performance of InGaN/GaN nanorod (NR) light emitting diodes (LEDs) fabricated by top-down RIE of c-plane GaN with InGaN quantum wells was investigated. After proper surface treatment a significantly improved device performance could be shown. Therefore, wet chemical removal of damaged material in KOH solution followed by atomic layer deposition of only 10 nm alumina as wide bandgap oxide for passivation were successfully applied. Raman spectroscopy revealed that the initially compressively strained InGaN/GaN LED layer stack turned into a virtually completely relaxed GaN and partially relaxed InGaN combination after RIE etching of NRs. Time-correlated single photon counting provides evidence that both treatments—chemical etching and alumina deposition—reduce the number of pathways for non-radiative recombination. Steady-state photoluminescence revealed that the luminescent performance of the NR LEDs is increased by about 50% after KOH and 80% after additional alumina passivation. Finally, complete NR LED devices with a suspended graphene contact were fabricated, for which the effectiveness of the alumina passivation was successfully demonstrated by electroluminescence measurements.
EAM Import::2019-03-13

Silicon dual pillar structure with a distributed Bragg reflector for dielectric laser accelerators: Design and fabrication - Yousefi, Peyman; McNeur, Joshua; Kozak, Martin; Niedermayer, Uwe; Gannott, Florentina; Lohse, Olga; Boine-Frankenheim, Oliver; Hommelhoff, Peter (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018)
Dielectric laser accelerators (DLAs) have proven to be good candidates for miniaturized particle accelerators. They rely on micro-fabricated dielectrics which are able to modulate the kinetic energy of the incoming electron beam under a proper laser illumination. In this paper we demonstrate a dual pillar structure with a distributed Bragg reflector to mimic a double sided illumination to the electron path. The structure is fabricated by an electron beam lithography technique followed by a cryogenic reactive ion etching process. Such a structure can accelerate the injected 28 keV electrons by a gradient of approximately 150 MeV/m which can be further optimized towards the GeV/m regim
Keywords: Dielectric laser accelerators; Dual pillar structure; Distributed Bragg reflector; Electron beam lithography; Cryogenic reactive ion etching

Simplified theory for ellipsoidal melted microlenses - Lindlein, Norbert; et al. (EOS Topical Meetings Digest Series, 1995)
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.optik.1optik.simpli

Simulating an interacting quantum gas with superconducting circuits - Eichler, Christopher (2014)
Simulating an Interacting Quantum Gas with Superconducting Circuits The high level of control achievable over quantized degrees of freedom have turned superconducting circuits into one of the prime physical architectures for quantum computing and simulation. While conventional approaches towards quantum information processing mostly rely on unitary time evolution, more recently open-system dynamics are considered for quantum simulations. In this talk, I will present experiments in which we use an open cavity QED system with tunable interactions to simulate the ground state of an interacting Bose gas confined in one dimension [1,2]. These experiments rely on the ability to efficiently measure higher order photon corrélations of the cavity output field. For this purpose we have developed a quantum limited amplifier achieving phase-preserving amplification at large bandwidth and high dynamic range [3]. Our results explore a different path towards the simulation of complex quantum many-body physics based on the controlled generation and detection of nonclassical radiation in an open quantum system. [1] S. Barrett et al., Phys. Rev. Lett. 110, 090501 (2013). [2] F. Verstraete and J. I. Cirac, Phys. Rev. Lett. 104, 190405 (2010). [3] C. Eichler et al., Phys. Rev. Lett. 113, 110502 (2014).
Keywords: wwwqudev

Simulating an Interacting Quantum Gas with Superconducting Circuits - Eichler, Christopher; et al. (APS March Meeting, 2015)
Keywords: wwwqudev

Simulating Dicke-like superradiance with classical light sources - Bhatti, Daniel; Oppel, Steffen; Wiegner, Ralph; Agarwal, Girish; von Zanthier, Joachim (Physical Review A, 2016)
In this paper we investigate the close relationship between Dicke superradiance, originally predicted for an ensemble of two-level atoms in entangled states, and the Hanbury Brown and Twiss effect, initially established in astronomy to determine the dimensions of classical light sources such as stars. By studying the state evolution of the fields produced by classical sources-defined by a positive Glauber-Sudarshan P function-when recording intensity correlations of higher order in a generalized Hanbury Brown and Twiss setup we find that the angular distribution of the last detected photon, apart from an offset, is identical to the superradiant emission pattern generated by an ensemble of two-level atoms in entangled symmetric Dicke states. We show that the phenomenon derives from projective measurements induced by the measurement of photons in the far field of the sources and the permutative superposition of quantum paths identical to those leading to superradiance in the case of single photon emitters. We thus point out an important similarity between classical sources and quantum emitters upon detection of photons if the particular photon source remains unknown. We finally present a compact result for the characteristic functional which generates intensity correlations of arbitrary order for any kind of light sourc

Simulating superradiance from higher-order-intensity-correlation measurements: Single atoms - Wiegner, Ralph; Oppel, Steffen; Bhatti, Daniel; von Zanthier, Joachim; Agarwal, G. S. (Physical Review A, 2015)
Superradiance typically requires preparation of atoms in highly entangled multiparticle states, the so-called Dicke states. In this paper we discuss an alternative route where we prepare such states from initially uncorrelated atoms by a measurement process. By measuring higher-order intensity-intensity correlations we demonstrate that we can simulate the emission characteristics of Dicke superradiance by starting with atoms in the fully excited state. We describe the essence of the scheme by first investigating two excited atoms. Here we demonstrate how via Hanbury Brown and Twiss type of measurements we can produce Dicke superradiance and subradiance displayed commonly with two atoms in the single excited symmetric and antisymmetric Dicke states, respectively. We thereafter generalize the scheme to arbitrary numbers of atoms and detectors, and explain in detail the mechanism which leads to this result. The approach shows that the Hanbury Brown and Twiss type of intensity interference and the phenomenon of Dicke superradiance can be regarded as two sides of the same coin. We also present a compact result for the characteristic functional which generates all order intensity-intensity correlation

Simulating the coupling of angular momenta in distant matter qubits - Ammon, C.; Maser, Andreas; Schilling, Uwe; Bastin, T.; von Zanthier, Joachim (Physical Review A, 2012)
We present a mathematical proof of the algorithm allowing one to generate all-symmetric and nonsymmetric-total angular momentum eigenstates in remote matter qubits by projective measurements, proposed in Maser et al. [Phys. Rev. A 79, 033833 (2009)]. By deriving a recursion formula for the algorithm we show that the generated states are equal to the total angular momentum eigenstates obtained via the usual quantum-mechanical coupling of angular momenta. In this way we demonstrate that the algorithm is able to simulate the coupling of N spin-1/2 systems, and to implement the required Clebsch-Gordan coefficients, even though the particles never directly interact with each othe

Simulating the photon stream of a real thermal light source - Schneider, Raimund; Biernoth, Christoph; Hölzl, Johannes; Pscherer, Andre; von Zanthier, Joachim (Applied Optics, 2018)
We present a computer algorithm capable of simulating the photon stream and the corresponding temporal photon statistics of thermal light sources. The algorithm implements realistic experimental conditions, incorporating the relevant parameters of the source as well as of the detection process. The code is verified by comparing the temporal photon autocorrelation function computed from the simulations to the one measured with a real thermal light source. In view of the renewed interest for intensity interferometry in astronomy and the life sciences, such simulations become increasingly relevant. (C) 2018 Optical Society of America

Simulation der Vorläuferpulse bei Fokussierung ultrakurzer optischer Laserpulse - Dehne, Henry; Loosen, Florian; Iff, Wolfgang; Lindlein, Norbert (Proceeding, 115. Jahrestagung der DGaO, 2014)
Ultrakurze Laserpulse sind sowohl in Wissenschaft und Forschung als auch in der Industrie aufgrund ihrer extrem kurzen zeitlichen Breite und hohen Intensität vielseitig einsetzbar. Hierbei sind Pulsdauern, mit einer Hauptfrequenz innerhalb des sichtbaren Spektrums, in einem Bereich von wenigen Femtosekunden realisierbar. Bei der Fokussierung dieser Pulse durch Linsen mit kreisförmiger Apertur tritt ein sogenannter Vorläuferpuls auf, der sich hinter dem Fokuspunkt vom Hauptpuls separiert und mit scheinbar Überlichtgeschwindigkeit ausbreitet. Dies ist keine Verletzung der Kausalität, da der Vorläuferpuls nur eine Interferenzerscheinung ist und keine Energie ins Fernfeld trägt. Der Vorläuferpuls entsteht durch die Beugung des Pulses an der Apertur und verursacht eine „Verzerrung“ des elektrischen Feldes im Fokusbereich. Durch Simulation kann der Einfluss von Parametern wie Polarisation und numerischer Apertur (NA) auf die Geschwindigkeit, Form und Amplitude des Vorläuferpulses bestimmt werden. Hierfür wird das Debye-Integral unter Berücksichtigung der einzelnen Frequenzkomponenten des Pulses verwendet.

Simulationen zur Erfassung der Güte gedruckter Polymer Optischer Wellenleiter (POWs) bei Variation signiﬁkanter Charakteristika - Loosen, Florian; Backhaus, Carsten; Vögl, Christian; Lindlein, Norbert (Proceeding, 119. DGaO-Jahrestagung, 2018)
Die Forschergruppe OPTAVER (Optische Aufbau- und Verbindungstechnik für baugruppenintegrierte Bussysteme) beschäftigt sich seit ca. 3 Jahren mit dem Design, der Simulation und dem Druckprozess Polymer Optischer Wellenleiter (POWs). Durch den eingesetzten additiven 3D-Fertigungsprozess (Flexodruck und Aerosol Jet Druck) der Wellenleiterstrukturen wird eine optische Simulation vorab unumgänglich, um die Güte der Wellenleiter simulativ zu überprüfen. In den vergangenen DGaO-Jahrestagungen wurde neben der Erweiterung des Simulationsmodells um einen Streuansatz (Dämpfungsberechnung) [1] auch eine Erweiterung bezüglich der Signaldispersion [2] dem wissenschaftlichen Publikum vorgestellt. Dämpfung und Signaldispersion legen vor allem die Güte des Wellenleiters als wichtige Kenngrößen fest. Diese Güte ist abhängig von der Variation signifikanter Charakteristika, wie Wellenleiterform, -pfad und Materialeigenschaften, welche simulativ untersucht werden müssen, um daraus Kenngrößen für die Wellenleiter zu erhalten. [1] F. Loosen et al. DGaO Proceedings C5 (2016) [2] C. Backhaus et al. DGaO Proceedings P8 (201

Simulation of micro-optical array systems with RAYTRACE - Lindlein, Norbert; et al. (Optical Engineering, 1998)
The optical analysis and design program RAYTRACE, which was developed at our institute, enables the simulation of micro-optical systems containing arrays of microlenses or other optical components. The most important features of the program are briefly described to show its broad application areas. A special simulation example showing the spot diagram and the intensity distribution in the focal plane of a simple Shack-Hartmann sensor with a diffractive microlens array for an incident aspherical wave is given. ©1998 Society of Photo-Optical Instrumentation Engineers.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.optik.1optik.simula
Keywords: Micro-optics; Microlens arrays; Optical design software; Ray tracing Shack-Hartmann wavefront sensor

Simulation of micro-optical systems including microlens arrays - Lindlein, Norbert (Journal of Optics A-Pure and Applied Optics, 2002)
The simulation of micro-optical systems, especially those including microlens arrays, is still a challenging task. There are of course traditional methods which can be applied under certain circumstances. This paper will discuss several geometrical optical and diffraction-based methods for the simulation of micro-optical systems. A simple paraxial geometrical optical matrix theory will be extended to the simulation of off-axis optical elements. Ray tracing will be used to model incoherent micro-optical systems. The propagation of Gaussian beams through off-axis optical systems using differential ray tracing will be discussed. The angular spectrum of plane waves will be used to propagate a scalar complex wave amplitude in free space simulating non-paraxial diffraction effects. Finally, a model will be proposed which combines ray tracing and wave propagation methods by converting a complex wave amplitude into rays and vice versa. In the case of wavefront warping a decomposition of the wave into elementary waves has to be performed. This combined model can take into account non-paraxial effects such as aberrations of optical elements and also diffraction effects.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.simula
Keywords: Optical system design; Wave propagation; Wavefronts and ray tracing

Simulations and experiments on polarization squeezing in optical fiber - Leuchs, Gerd; et al. (Physical Review A, 2008)
We investigate polarization squeezing of ultrashort pulses in optical fiber, over a wide range of input energies and fiber lengths. Comparisons are made between experimental data and quantum dynamical simulations to find good quantitative agreement. The numerical calculations, performed using both truncated Wigner and exact +P phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonon variables. The simulations reveal that excess phase noise, such as from depolarizing guided acoustic wave Brillouin scattering, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fiber lengths. We also calculate the optimum fiber length for maximum squeezing. © 2008 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.optik.1optik.simula

Simulations of the secondary maxima of highly focused ultrashort optical pulses in the focal plane - Fries, Sebastian; Loosen, Florian; Lindlein, Norbert (Proceeding, 116. Jahrestagung der DGaO, 2015)
Nowadays, ultrashort optical pulses have quite a few applications, e.g. in the measuring technology, in the processing of materials, and also in the medical science. Like in the stationary (continuous wave) case, secondary maxima appear in the focal plane, when optical pulses are focused by an aplanatic lens (without aberrations). These can be simulated by adding frequency dependent Debye integrals, where each of them can be considered as a superposition of plane waves travelling from the exit pupil to the focus. By changing the order of integrations this corresponds to a superposition of waves with plane wavefront, but time-dependent amplitude. The secondary maxima are highly dependent on the duration of the pulse. Depending on the parameters of the pulse and the lens, they have a maximum intensity at a certain duration, and seemingly vanish as the duration of the pulse grows shorter. The latter results from the fact, that at any non-axial point in the focal plane the amplitude of the envelope of some of these “plane waves” diminishes. Via simulations the effects of certain parameters, such as polarisation, numerical aperture, and initial amplitude profile can be analysed.

Simultaneous characterization of the quality and orientation of cylindrical lens surfaces - Mantel, Klaus Peter; Lindlein, Norbert; Schwider, Johannes (Applied Optics, 2005)
A diffractive grazing-incidence interferometer for the test of cylindrical lenses is described. Besides surface aberrations from the ideal shape, the interferometer allows for the simultaneous determination of the relative position and orientation of surfaces to another. The measurement principle as well as a classification of deviation types is given. Measurement results for planar concave lenses are presented. © 2005 Optical Society of America.
UnivIS-Import:2015-04-14:Pub.2005.nat.dphy.optik.1optik.simult

Simultaneous Generation of X-ray and Range Images using XCAT under Motion - Rybakov, Oleksiy; Bier, Bastian; Maier, Jennifer; Unberath, Mathias; Maier, Andreas (2017 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2017)
Novel algorithms in the field of X-ray imaging are commonly evaluated on simulation software first, before they are implemented on a clinical scanner in order to test their performance in a very controlled setup. This reduces patient dose and facilitates the development of new approaches and methods. In recent years, range imaging applications were established in the field of medical imaging. Range imaging showed its potential in radiotherapy, augmented reality, and, recently, also for motion correction in cone-beam computed tomography. In this work, we present an open-source software tool that allows to generate X-ray projections and surface information in one step completely on the graphics processing unit. To this end, we extend a state-of-the-art rendering method based on an append buffer. Arbitrary imaging geometries for the X-ray source and the range imaging camera can be selected. We test the proposed method on the XCAT phantom in two fundamentally different scenarios: a weight-bearing acquisition showing a squat, and a supine acquisition of a breathing patien
Keywords: range imaging; x-ray imaging; append buffer; weight-bearing; open-source; XCAT

Simultaneous measurement of phase and local orientation of linearly polarized light: Implementation and measurement results - Rothau, Sergej; Kellermann, Christine; Nercissian, Vanusch; Berger, Andreas; Mantel, Klaus; Lindlein, Norbert; Lindlein, Norbert (Applied Optics, 2014)
Optical components manipulating both polarization and phase of wave fields find many applications in today's optical systems. With modern lithography methods it is possible to fabricate optical elements with nanostructured surfaces from different materials capable of generating spatially varying, locally linearly polarized-light distributions, tailored to the application in question. Since such elements in general also affect the phase of the light field, the characterization of the function of such elements consists in measuring the phase and the polarization of the generated light, preferably at the same time. Here, we will present first results of an interferometric approach for a simultaneous and spatially resolved measurement of both phase and polarization, as long as the local polarization at any point is linear (e.g., for radially or azimuthally polarized light).

Simultaneous measurement of phase transmission and birefringence of an object under test - Rothau, Sergej; Mantel, Klaus; Lindlein, Norbert (Applied Optics, 2018)
This paper presents a novel interferometric method for the simultaneous spatially resolved analysis of an object under test regarding the phase transmission function and the magnitude and orientation of the (uniaxial) birefringence. The measurement strategy is based on variations of the phase and polarization and processing the interference patterns so obtained. With this method, which is very similar to the classical phase-shifting interferometry, a complete analysis of birefringent properties of the object and its impact on the phase of the incoming light can be done in one measurement cycle. The theoretical description of the investigated methods and their experimental implementation are presented.
Keywords: Fringe analysis; Interferometry; Phase measurement; Polarimetry; Birefringence; Polarization; Phase measurement; Phase shift; Phase shifting interferometry; Polymer liquid crystals; Refractive index; Stress birefringence

Simultaneous measurement of phase transmission and linear or circular dichroism of an object under test - Rothau, Sergej; Rao, Xiao; Lindlein, Norbert (Applied Optics, 2019)

Simultane Vermessung der Phase und der räumlich variierenden linearen Polarisation - Rothau, Sergej; Nercissian, Vanusch; Berger, Andreas; Lindlein, Norbert (114. Jahrestagung der DGaO, 2013)

Single-cycle pulse compression at 10 MHz repetition rate in gas-filled hollow-core photonic crystal fiber - Schade, Daniel; Köttig, F.; Koehler, J. R.; Frosz, M. H.; Tani, F.; Russell, Philip St. John (Optics InfoBase Conference Papers, 2020)
Fiber laser pulses at 1030 nm are compressed from 340 fs to 3.8 fs at repetition rates up to 10 MHz in a two-stage setup using gas-filled single-ring photonic crystal fibers with >70% total transmission.
CRIS-Team Scopus Importer:2021-04-19

Single-mode hollow-core photonic crystal fiber made from soft glass - Jiang, Xin; Euser, T. G.; Abdolvand, Amir; Babic, F.; Tani, Francesco; Joly, Nicolas; Travers, J. C.; Russell, Philip St. John (Optics Express, 2011)
We demonstrate the first soft-glass hollow core photonic crystal fiber. The fiber is made from a high-index lead-silicate glass (Schott SF6, refractive index 1.82 at 500 nm). Fabricated by the stack-and-draw technique, the fiber incorporates a 7-cell hollow core embedded in a highly uniform 6-layer cladding structure that resembles a kagomé-like lattice. Effective single mode guidance of light is observed from 750 to 1050 nm in a large mode area (core diameter 30 µm) with a low loss of 0.74 dB/m. The underlying guidance mechanism of the fiber is investigated using finite element modeling. The fiber is promising for applications requiring single mode guidance in a large mode area, such as particle guidance, fluid and gas filled devices.
EAM Import::2019-03-13

Single-mode squeezing in arbitrary spatial modes - Semmler, Marion; Berg-Johansen, Stefan; Chille, Vanessa; Gabriel, Christian; Banzer, Peter; Aiello, Andrea; Marquardt, Christoph; Leuchs, Gerd (Optics Express, 2016)
As the generation of squeezed states of light has become a standard technique in laboratories, attention is increasingly directed towards adapting the optical parameters of squeezed beams to the specific requirements of individual applications. It is known that imaging, metrology, and quantum information may benefit from using squeezed light with a tailored transverse spatial mode. However, experiments have so far been limited to generating only a few squeezed spatial modes within a given setup. Here, we present the generation of single-mode squeezing in Laguerre-Gauss and Bessel-Gauss modes, as well as an arbitrary intensity pattern, all from a single setup using a spatial light modulator (SLM). The degree of squeezing obtained is limited mainly by the initial squeezing and diffractive losses introduced by the SLM, while no excess noise from the SLM is detectable at the measured sideband. The experiment illustrates the single-mode concept in quantum optics and demonstrates the viability of current SLMs as flexible tools for the spatial reshaping of squeezed light.
CRIS-Team Scopus Importer:2022-06-05

Single-Molecule Vacuum Rabi Splitting: Four-Wave Mixing and Optical Switching at the Single-Photon Level - Pscherer, André; Meierhofer, Manuel; Wang, Daqing; Kelkar, Hrishikesh; Martín-Cano, Diego; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Physical Review Letters, 2021)
A single quantum emitter can possess a very strong intrinsic nonlinearity, but its overall promise for nonlinear effects is hampered by the challenge of efficient coupling to incident photons. Common nonlinear optical materials, on the other hand, are easy to couple to but are bulky, imposing a severe limitation on the miniaturization of photonic systems. In this Letter, we show that a single organic molecule acts as an extremely efficient nonlinear optical element in the strong coupling regime of cavity quantum electrodynamics. We report on single-photon sensitivity in nonlinear signal generation and all-optical switching. Our work promotes the use of molecules for applications such as integrated photonic circuits operating at very low powers.
CRIS-Team Scopus Importer:2021-10-08

Single Photons Emitted by Nanocrystals Optically Trapped in a Deep Parabolic Mirror - Salakhutdinov, Vsevolod; Sondermann, Markus; Carbone, Luigi; Giacobino, Elisabeth; Bramati, Alberto; Leuchs, Gerd (Physical Review Letters, 2020)

Single photon sources for quantum radiometry: a brief review about the current state-of-the-art - Kueck, Stefan; Lopez, Marco; Hofer, Helmuth; Georgieva, Hristina; Christinck, Justus; Rodiek, Beatrice; Porrovecchio, Geiland; Smid, Marek; Götzinger, Stephan; Becher, Christoph; Fuchs, Philipp; Lombardi, Pietro; et al. (Applied Physics B-Lasers and Optics, 2022)
Single-photon sources have a variety of applications. One of these is quantum radiometry, which is reported on in this paper in the form of an overview, specifically of the current state of the art in the application of deterministic single photon sources to the calibration of single photon detectors. To optimize single-photon sources for this purpose, extensive research is currently carried out at the European National Metrology Institutes (NMIs), in collaboration with partners from universities. Single-photon sources of different types are currently under investigation, including sources based on defect centres in (nano-)diamonds, on molecules and on semiconductor quantum dots. We will present, summarise, and compare the current results obtained at European NMIs for single-photon sources in terms of photon flux, single-photon purity, and spectral power distribution as well as the results of single-photon detector calibrations carried out with this type of light sources.
CRIS-Team Scopus Importer:2022-02-04

Single-shot reconstruction of spectral amplitude and phase in a fiber ring cavity at a 80 MHz repetition rate - Hammer, Jonas; Hosseini, P.; Menyuk, C. R.; Russell, Philip St. John; Joly, Nicolas (Optics Letters, 2016)
Femtosecond pulses circulating in a synchronously driven fiber ring cavity have complex amplitude and phase profiles that can change completely from one round-trip to the next. We use a recently developed technique, combining dispersive Fourier transformation) with spectral interferometry, to reconstruct the spectral amplitude and phase at each round-trip and, thereby, follow in detail the pulse reorganization that occurs. We focus on two different regimes: a period-two regime in which the pulse alternates between two distinct states and a highly complex regime. We characterize the spectral amplitude and phase of the pulses in both regimes at a repetition rate of 75.6 MHz and find good agreement with modeling of the system based on numerical solutions of the generalized nonlinear Schrodinger equation with feedback. (C) 2016 Optical Society of America

Single sideband microwave to optical photon conversion-an electro-optic realization - Rueda, Alfredo; Sedlmeir, Florian; Collodo, Michele; Vogl, Ulrich; Stiller, Birgit; Schunk, Gerhard; Strekalov, Dmitry V.; Marquardt, Christoph; Fink, Johannes M.; Painter, Oskar; Leuchs, Gerd; Schwefel, Harald G.L. (Optics InfoBase Conference Papers, 2017)
We present results on nonlinear electro-optical conversion of microwave radiation into the optical telecommunication band with more than 0.1% photon number conversion efficiency with MHz bandwidth, in a crystalline whispering gallery mode resonator.
CRIS-Team Scopus Importer:2021-06-29

Single-Step Process for Titanium Surface Micro-and Nano-Structuring and In Situ Silver Nanoparticles Formation by Ultra-Short Laser Patterning - Aceti, Dante Maria; Filipov, Emil; Angelova, Liliya; Sotelo, Lamborghini; Fontanot, Tommaso; Yousefi, Peyman; Christiansen, Silke; Leuchs, Gerd; Stanimirov, Stanislav; Trifonov, Anton; Buchvarov, Ivan; Daskalova, Albena (Materials, 2022)
Ultra-short laser (USL)-induced surface structuring combined with nanoparticles synthesis by multiphoton photoreduction represents a novel single-step approach for commercially pure titanium (cp-Ti) surface enhancement. Such a combination leads to the formation of distinct topographical features covered by nanoparticles. The USL processing of cp-Ti in an aqueous solu-tion of silver nitrate (AgNO3) induces the formation of micron-sized spikes surmounted by silver nanoparticles (AgNPs). The proposed approach combines the structuring and oxidation of the Ti surface and the synthesis of AgNPs in a one-step process, without the use of additional chemicals or a complex apparatus. Such a process is easy to implement, versatile and sustainable compared to alternative methodologies capable of obtaining comparable results. Antimicrobial surfaces on medical devices (e.g., surgical tools or implants), for which titanium is widely used, can be realized due to the simultaneous presence of AgNPs and micro/nano-structured surface topography. The pro-cessed surfaces were examined by means of a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and Raman spectroscopy. The surface morphology and the oxidation, quality and quantity of AgNPs were analyzed in relation to process parameters (laser scanning speed and AgNO3 concentration), as well as the effect of AgNPs on the Raman signal of Titanium oxide.
CRIS-Team Scopus Importer:2022-07-22
Keywords: laser ablation; multiphoton photo-reduction; silver nanoparticles; surface patterning; titanium; ultra-short laser processing

Slow waves on magnetic metamaterials and on chains of plasmonic nanoparticles: Driven solutions in the presence of retardation - Zhuromskyy, Oleksandr; Sydoruk, Oleksiy; Shamonina, E.; Solymar, L. (Journal of Applied Physics, 2009)
Slow waves on chains or lattices of resonant elements offer a unique tool for guiding and manipulating the electromagnetic radiation on a subwavelength scale. Applications range from radio waves to optics with two major classes of structures being used: (i) metamaterials made of coupled ring resonators supporting magnetoinductive waves and (ii) plasmonic crystals made of nanoparticles supporting waves of near-field coupling. We derive dispersion equations of both types of slow waves for the case when the interelement coupling is governed by retardation effects, and show how closely they are related. The current distribution is found from Kirchhoff's equation by inverting the impedance matrix. In contrast to previous treatments power conservation is demonstrated in a form relevant to a finite structure: the input power is shown to be equal to the radiated power plus the powers absorbed in the Ohmic resistance of the elements and the terminal impedance. The relations between frequency and wave number are determined for a 500-element line for two excitations using three different methods. Our approach of retrieval of the dispersion from driven solutions of finite lines is relevant for practical applications and may be used in the design of metamaterials and plasmonic crystals with desired properties.
EAM Import::2019-03-13

Small leucine-rich proteoglycans inhibit CNS regeneration by modifying the structural and mechanical properties of the lesion environment - Kolb, Julia; Tsata, Vasiliki; John, Nora; Kim, Kyoohyun; Möckel, Conrad; Rosso, Gonzalo; Kurbel, Veronika; Parmar, Asha; Sharma, Gargi; Karandasheva, Kristina; Abuhattum, Shada; Lyraki, Olga; et al. (Nature Communications, 2023)
Extracellular matrix (ECM) deposition after central nervous system (CNS) injury leads to inhibitory scarring in humans and other mammals, whereas it facilitates axon regeneration in the zebrafish. However, the molecular basis of these different fates is not understood. Here, we identify small leucine-rich proteoglycans (SLRPs) as a contributing factor to regeneration failure in mammals. We demonstrate that the SLRPs chondroadherin, fibromodulin, lumican, and prolargin are enriched in rodent and human but not zebrafish CNS lesions. Targeting SLRPs to the zebrafish injury ECM inhibits axon regeneration and functional recovery. Mechanistically, we find that SLRPs confer mechano-structural properties to the lesion environment that are adverse to axon growth. Our study reveals SLRPs as inhibitory ECM factors that impair axon regeneration by modifying tissue mechanics and structure, and identifies their enrichment as a feature of human brain and spinal cord lesions. These findings imply that SLRPs may be targets for therapeutic strategies to promote CNS regeneration.<br
Keywords: Biophysics; Mechanisms of disease; Spinal cord injury

Soliton back-action evading measurement using spectral filtering - Leuchs, Gerd; et al. (Physical Review A, 2002)
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.solito

Sparse Active Triangulation Grids for Respiratory Motion Management - Bauer, Sebastian; Ettl, Svenja; Wasza, Jakob; Willomitzer, Florian; Huber, Franz; Hornegger, Joachim; Häusler, Gerd (DGaO Proceedings 2012, 2012)

Spatial Herodyn-Spektrometer zur Temperaturmessung in der mittleren Atmosphäre - Wagner, Fritz; Mantel, Klaus; Loosen, Florian; Deiml, Michael; Olschewski, Friedhelm; Kaufmann, Martin (Proceeding, 118. DGaO-Jahrestagung, 2017)
Die Atmosphäre der Erde wird durch eine Vielzahl von chemischen und physikalischen Kopplungsvorgängen beeinflusst, deren Verständnis noch einige Lücken aufweist. Um die Dynamik der dort ablaufenden physikalischen Prozesse zu untersuchen und damit Wetter- und Klimamodelle testen und verbessern zu können, bedarf es der Messung atmosphärischer Daten auf einer globalen Skala und mit hoher zeitlicher und räumlicher Auflösung. Die „Initiative zur Entwicklung von Kleinsatelliten für die Erforschung von Klimaprozessen mittels Tomographie“ (DISSECT) hat sich zum Ziel gesetzt, die Zusammensetzung und Dynamik der mittleren Atmosphäre mittels Fernerkundung durchzuführen. In einem ersten Projekt werden Kleinsatelliten (CubeSats) mit sog. Spatialen Heterodyn-Spektrometern ausgerüstet, die die Temperaturverteilung der mittleren Atmosphäre spektroskopisch bestimmen sollen, indem die Intensitätsverhältnisse gewisser Linien im A-Band des Sauerstoffs gemessen werden. Der Beitrag beschreibt Design und Herstellung eines solchen Spektrometers sowie der verwendeten optischen Systeme des Kleinsatelliten. Ein erster Test des Systems erfolgt im März 2017 im Rahmen des REXUS-Projekts von DLR, SNSB und ESA.

Spatially-controlled laser-induced decoration of 2D and 3D substrates with plasmonic nanoparticles - Bashouti, M. Y.; Povolotckaia, A. V.; Povolotskiy, A. V.; Tunik, S. P.; Christiansen, S. H.; Leuchs, Gerd; Manshina, A. A. (RSC Advances, 2016)
We demonstrate a new approach which can be used for targeted imparting of plasmonic properties for a wide range of different substrates (transparent and non-transparent) which may have any 2D or 3D topological structure created independently in a prior step with some other technology.
EAM Import::2019-03-13

Spatially resolved spectroscopy of alkali metal vapour diffusing inside hollow-core photonic crystal fibres - Häupl, Daniel; Weller, Daniel; Loew, Robert; Joly, Nicolas (New Journal of Physics, 2022)
We present a new type of compact and all-glass based vapour cell integrating hollow-core photonic crystal fibres. The absence of metals, as in a traditional vacuum chamber and the much more compact geometry allows for fast and homogeneous heating. As a consequence we can fill the fibres on much faster timescales, ranging from minutes to hours. Additionally the all-glass design ensures optical access along the fibre. This allows live monitoring of the diffusion of rubidium atoms inside the hollow-core by measuring the frequency-dependent fluorescence from the atoms. The atomic density is numerically retrieved using a five-level system of Bloch-equations.
CRIS-Team WoS Importer:2022-11-25

Specialty photonic crystal fibers and their applications - Novoa, David; Joly, Nicolas (Crystals, 2021)
CRIS-Team Scopus Importer:2021-07-16

Spectral broadening of femtosecond UV pulses in air-filled hollow-core photonic crystal fiber - Luan, J.; Novoa, D.; Russell, Philip St. John (Optics InfoBase Conference Papers, 2020)
Air-filled kagomé-type photonic crystal fiber pumped by 40-fs pulses at 400 nm produces a spectrum with several nitrogen-related Raman bands that is broad enough to support transform-limited 7 fs pulses in the UV.
CRIS-Team Scopus Importer:2020-11-13

Spectral extension and synchronization of microcombs in a single microresonator - Zhang, Shuangyou; Silver, Jonathan M.; Bi, Toby; Del'Haye, Pascal (Nature Communications, 2020)
Broadband optical frequency combs are extremely versatile tools for precision spectroscopy, ultrafast ranging, as channel generators for telecom networks, and for many other metrology applications. Here, we demonstrate that the optical spectrum of a soliton microcomb generated in a microresonator can be extended by bichromatic pumping: one laser with a wavelength in the anomalous dispersion regime of the microresonator generates a bright soliton microcomb while another laser in the normal dispersion regime both compensates the thermal effect of the microresonator and generates a repetition-rate-synchronized second frequency comb. Numerical simulations agree well with experimental results and reveal that a bright optical pulse from the second pump is passively formed in the normal dispersion regime and trapped by the primary soliton. In addition, we demonstrate that a dispersive wave can be generated and influenced by cross-phase-modulation-mediated repetition-rate synchronization of the two combs. The demonstrated technique provides an alternative way to generate broadband microcombs and enables the selective enhancement of optical power in specific parts of a comb spectrum.
CRIS-Team Scopus Importer:2020-12-25

Spectral extension of microcombs with two seed lasers - Zhang, Shuangyou; Silver, Jonathan M.; Bi, Toby; Del'Haye, Pascal (Optics InfoBase Conference Papers, 2021)
We demonstrate the spectral extension of microcombs by bichromatic pumping of a single microresonator. One of the seed lasers generates a soliton that synchronizes with the repetition rate of the second frequency comb via cross-phase modulation.
CRIS-Team Scopus Importer:2021-12-03

Spectral properties of second, third and fourth harmonics generation from broadband multimode bright squeezed vacuum - Kopylov, Denis A.; Rasputnyi, Andrei; Murzina, Tatiana; Chekhova, Maria (Laser Physics Letters, 2020)
We study theoretically the spectra of second, third and fourth harmonics from multimode bright squeezed vacuum obtained by type-I broadband high-gain parametric down conversion. The different contributions to the spectra of harmonics are analyzed. A new method for the measurement of second-order correlation function g((2))(0) of parametric down conversion radiation is suggested.
CRIS-Team WoS Importer:2020-06-26

Spectral Radar: OCT in the Fourier Domain - Häusler, Gerd; et al. (Handbook of Optical Coherence Tomography, 2001)
UnivIS-Import:2015-04-20:Pub.2001.nat.dphy.optik.1optik.spectr

Spin-orbit coupling affecting the evolution of transverse spin - Eismann, Joerg S.; Banzer, Peter; Neugebauer, Martin (Physical Review Research, 2019)
We investigate the evolution of transverse spin in tightly focused circularly polarized beams of light, where spin-orbit coupling causes a local rotation of the polarization ellipses upon propagation through the focal volume. The effect can be explained as a relative Gouy-phase shift between the circularly polarized transverse field and the longitudinal field carrying orbital angular momentum. The corresponding rotation of the spatial distribution of the electric transverse spin density is observed experimentally by utilizing a recently developed reconstruction scheme, which relies on transverse-spin-dependent directional scattering of a nanoprobe.
CRIS-Team WoS Importer:2021-10-18

Spin-orbit interaction in nanofiber-based Brillouin scattering - Zerbib, Maxime; Romanet, Maxime; Sylvestre, Thibaut; Wolff, Christian; Stiller, Birgit; Beugnot, Jean Charles; Huy, Kien Phan (Optics Express, 2023)
Angular momentum is an important physical property that plays a key role in light-matter interactions, such as spin-orbit interaction. Here, we investigate theoretically and experimentally the spin-orbit interaction between a circularly polarized optical (spin) and a transverse vortex acoustic wave (orbital) using Brillouin backscattering in a silica optical nanofiber. We specifically explore the state of polarization of Brillouin backscattering induced by the TR21 torso-radial vortex acoustic mode that carries an orbital angular momentum. Using a full-vectorial theoretical model, we predict and observe two operating regimes for which the backscattered Brillouin signal is either depolarized or circularly polarized, depending on the input pump polarization. We demonstrate that when the pump is circularly polarized and thus carries a spin angular momentum, the backscattered signal undergoes a handedness reversal of circular polarization due to opto-acoustic spin-orbit interaction and the conservation of overall angular momentum.
CRIS-Team Scopus Importer:2023-07-21

Spontaneous Parametric Down-Conversion in Nonlinear Metasurfaces - Fedotova, Anna; Santiago Cruz, Tomás; Sultanov, Vitaliy; Weissflog, Maximilian; Younesi, Mohammadreza; Staude, Isabelle; Pertsch, Thomas; Setzpfandt, Frank; Chekhova, Maria (2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021, 2021)
Resonant nonlinear metasurfaces gained a lot of interest in the past decade because of their unique features such as subwavelength thickness and ability to control spatial and temporal properties of light. They have proved to be efficient for classical processes such as second-harmonic generation (SHG), but their potential in quantum nanophotonics - for example for biphoton generation via spontaneous parametric down-conversion (SPDC) - remained mostly unexplored. Recently, SPDC at the nanoscale was established in nonlinear thin films [1] and implied in single nanoresonators [2], albeit with very low efficiency.
CRIS-Team Scopus Importer:2021-10-29

Squeezed light and self-induced transparency in mercury-filled hollow core photonic crystal fibers - Vogl, Ulrich; Joly, Nicolas Y.; Russell, Philip St J.; Marquardt, Christoph; Leuchs, Gerd (Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015, 2015)
We successfully demonstrate squeezing of nanosecond pulses via self-induced transparency in a system of mercury vapor confined in a hollow core kagomé-style fiber.
CRIS-Team Scopus Importer:2022-06-05

Squeezed Light from Microstructured Fibres: Towards Free Space Quantum Cryptography - Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 2001)
Amplitude-squeezed pulsed light has been produced using a microstructured silica fibre. By spectrally filtering after the non-linear propagation in the fibre a squeezing value of - 1.7 dB has been measured. A quantum key distribution scheme based on squeezed light from such microstructured fibres is proposed.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.squeez

Squeezed-state purification with linear optics and feedforward - Leuchs, Gerd; et al. (Physical Review Letters, 2006)
A scheme for optimal and deterministic linear optical purification of mixed squeezed Gaussian states is proposed and experimentally demonstrated. The scheme requires only linear optical elements and homodyne detectors, and allows the balance between purification efficacy and squeezing degradation to be controlled. One particular choice of parameters gave a tenfold reduction of the thermal noise with a corresponding squeezing degradation of only 11%. We prove optimality of the protocol, and show that it can be used to enhance the performance of quantum informational protocols such as dense coding and entanglement generation. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.squeez

Squeezed vacuum states from a whispering gallery mode resonator - Otterpohl, Alexander; Sedlmeir, Florian; Shafiee, Golnoush; Dirmeier, Thomas; Vogl, Ulrich; Schunk, Gerhard; Strekalov, Dmitry V.; Schwefel, Harald G.L.; Gehring, Tobias; Andersen, Ulrik L.; Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2018)
We demonstrate the generation of squeezed vacuum states of light in a crystalline whispering gallery mode resonator. We utilize a millimeter-sized lithium niobate resonator with strong optical second order nonlinearity. This system allows us to reach 1.2 dB of squeezing at a pump power of only 300 μW and offers hereby a compact and power efficient source of squeezed vacuum states of light.
CRIS-Team Scopus Importer:2022-06-05

Squeezed vacuum states from a whispering gallery mode resonator - Otterpohl, Alexander; Sedlmeir, Florian; Vogl, Ulrich; Dirmeier, Thomas; Shafiee, Golnoush; Schunk, Gerhard; Strekalov, Dmitry V.; Schwefel, Harald; Gehring, Tobias; Andersen, Ulrik Lund; Leuchs, Gerd; Marquardt, Christoph (Optica, 2019)
Squeezed vacuum states enable optical measurements below the quantum limit and hence are a valuable resource for applications in quantum metrology and also quantum communication. However, most available sources require high pump powers in the milliwatt range and large setups that hinder real-world applications. Furthermore, degenerate operation of such systems presents a challenge. Here, we use a compact crystalline whispering gallery mode resonator made of lithium niobate as a degenerate parametric oscillator. We demonstrate about 1.4 dB noise reduction below the shot-noise level for only 300 mu W of pump power in degenerate single-mode operation. Furthermore, we report a record pump threshold as low as 1.35 mu W. Our results show that the whispering gallery-based approach presents a promising platform for a compact and efficient source for nonclassical light. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
CRIS-Team WoS Importer:2019-12-06

Squeezing by self induced transparency in Rb filled hollow core fibers - Zhong, Wenjia; Marquardt, Christoph; Leuchs, Gerd; Andersen, U. L.; Light, P; Couny, F.; Benabid, F. (2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007)
There is great interest in photonic crystal fibers (PCFs) because of their potential for hosting highly nonlinear material. Already with material of low nonlinearity such as silica for solid core PCFs, the nonlinear properties can be utilized since high intensities of light are guided within the core. To create squeezed states, we plan to exploit the high nonlinearity of resonant Rb vapor filled in the hollow fiber core and to use self-induced transparency (SIT) solitons to avoid resonant loss. High nonlinearity is induced from the self-phase modulation of a detuned 2pi soliton. Photon-phonon interactions, which cause a significant amount of excess noise in solid core fibers, will be highly reduced in our system.<br
Keywords: Resonance; Optical fiber theory; Photonics; Crystalline materials; Fiber nonlinear optics; Optical solitons; Solids; Atom optics; Physics; Optical materials

Stabilization of transmittance fluctuations caused by beam wandering in continuous-variable quantum communication over free-space atmospheric channels - Usenko, Vladyslav C.; Peuntinger, Christian; Heim, Bettina; Guenthner, Kevin; Derkach, Ivan; Elser, Dominique; Marquardt, Christoph; Filip, Radim; Leuchs, Gerd (Optics Express, 2018)
Transmittance fluctuations in turbulent atmospheric channels result in quadrature excess noise which limits applicability of continuous-variable quantum communication. Such fluctuations are commonly caused by beam wandering around the receiving aperture. We study the possibility to stabilize the fluctuations by expanding the beam, and test this channel stabilization in regard of continuous-variable entanglement sharing and quantum key distribution. We perform transmittance measurements of a real free-space atmospheric channel for different beam widths and show that the beam expansion reduces the fluctuations of the channel transmittance by the cost of an increased overall loss. We also theoretically study the possibility to share an entangled state or to establish secure quantum key distribution over the turbulent atmospheric channels with varying beam widths. We show the positive effect of channel stabilization by beam expansion on continuous-variable quantum communication as well as the necessity to optimize the method in order to maximize the secret key rate or the amount of shared entanglement. Being autonomous and not requiring adaptive control of the source and detectors based on characterization of beam wandering, the method of beam expansion can be also combined with other methods aiming at stabilizing the fluctuating free-space atmospheric channels.
CRIS-Team Scopus Importer:2022-06-05

Stitching errors in diffractive nulltest elements - Berger, Andreas; Harder, Irina; Nercissian, Vanusch; Mantel, Klaus Peter; Lindlein, Norbert (DGaO Proceedings, 2012)

Strong optoacoustic interaction in hot CS2-filled liquid-core optical fiber - Geilen, Andreas; Popp, Alexandra; Walter, Daniel; Chemnitz, Mario; Junaid, Saher; Poulton, Christopher G.; Marquardt, Christoph; Schmidt, Markus A.; Stiller, Birgit (2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021, 2021)
Optical fibers with a liquid core provide a versatile platform for nonlinear optics [1]. Filled with carbon disulfide (CS 2 ), the high linear refractive index of 1.59 at 1549 nm and low speed of sound of 1250 ms -1 , compared to silica, ensures guidance of optical and acoustic waves inside the fiber core. This type of fiber also provides a large optoacoustic interaction via stimulated Brillouin scattering (SBS) [2] due to the high optical nonlinearity of CS 2 , as well as the long interaction length and the low optical loss.
CRIS-Team Scopus Importer:2021-10-29

Strong plasmonic enhancement of biexciton emission: Controlled coupling of a single quantum dot to a gold nanocone antenna - Matsuzaki, Korenobu; Vassant, Simon; Liu, Hsuan-Wei; Dutschke, Anke; Hoffmann, Björn; Chen, Xuewen; Christiansen, Silke; Buck, Matthew R.; Hollingsworth, Jennifer A.; Götzinger, Stephan; Sandoghdar, Vahid (Scientific Reports, 2017)
Multiexcitonic transitions and emission of several photons per excitation comprise a very attractive feature of semiconductor quantum dots for optoelectronics applications. However, these higher-order radiative processes are usually quenched in colloidal quantum dots by Auger and other nonradiative decay channels. To increase the multiexcitonic quantum efficiency, several groups have explored plasmonic enhancement, so far with moderate results. By controlled positioning of individual quantum dots in the near field of gold nanocone antennas, we enhance the radiative decay rates of monoexcitons and biexcitons by 109 and 100 folds at quantum efficiencies of 60 and 70%, respectively, in very good agreement with the outcome of numerical calculations. We discuss the implications of our work for future fundamental and applied research in nano-optics.

Structured quantum projectiles - Larocque, Hugo; Fickler, Robert; Cohen, Eliahu; Grillo, Vincenzo; Dunin-Borkowski, Rafal E.; Leuchs, Gerd; Karimi, Ebrahim (Physical Review A, 2019)
Matter wave interferometry is becoming an increasingly important technique in quantum metrology. However, unlike its photonic counterpart, this technique relies on the interference of particles possessing a nonzero rest mass and an electric charge. Matter waves can therefore experience alterations in their wavelike features while propagating through uniform fields to which a linear potential can be attributed, e.g., the Newtonian gravitational potential. Here, we derive the propagation kernel attributed to matter waves within such a potential. This kernel thereafter allows us to provide analytical formulations for structured matter waves subjected to a linear potential. Our formulations are in agreement with both the classical dynamics attributed to such waves and with previous interferometry experiments. Eigenbasis representations of structured matter waves are also introduced along with their application to enhanced interferometric measurements. Our results are not only relevant to matter wave interferometry, but also emphasize its fundamental differences with respect to photonic interferometry.
CRIS-Team WoS Importer:2019-03-15

Strukturierungsfehler diffraktiv optischer Elemente - Berger, Andreas; Harder, Irina; Lohse, Olga; Lindlein, Norbert (114. Jahrestagung der DGaO, 2013)

Study of broadband multimode light via non-phase-matched sum frequency generation - Kopylov, Denis A.; Spasibko, Kirill; Murzina, Tatiana; Chekhova, Maria (New Journal of Physics, 2019)
We propose non-phase-matched sum frequency generation (SFG) as a method for characterizing broadband multimode light. Both the central wavelength and the bandwidth are in this case not limited by the phase matching condition. As an example, we consider bright squeezed vacuum (BSV) generated through high-gain parametric down conversion (PDC). In the spectrum of SFG from BSV, we observe the coherent peak and the incoherent background. We show that the ratio of their widths is equal to the number of frequency modes in BSV, which in the case of low-gain PDC gives the degree of frequency entanglement for photon pairs. By generating the sum frequency in the near-surface region of a nonlinear crystal, we increase the SFG efficiency and get rid of the modulation caused by chromatic dispersion, known as Maker fringes. This allows one to use non-phasematched SFG as a wavelength-independent autocorrelator. Furthermore, we demonstrate efficient non-phase-matched three- and four-frequency summation of broadband multimode light, hardly possible under phase matching. We show that the latter contains the coherent peak while the former does not.
CRIS-Team WoS Importer:2019-04-12

Study of mass transfer in supercritical carbon dioxide (SCCO2) using optical methods - Hu, Miao; Benning, Rainer; Delgado, Antonio; Ertunc, Özgür; Nercissian, Vanusch; Berger, M. (Heat and Mass Transfer, 2017)
The purpose of this work is to design and develop a type of experiment setup that would enable the direct observation of steady diffusion process in situ. Two different optical methods - shadowgraph and shearing interferometry - were used for the first time to visualise and quantitatively analyse the diffusion around a droplet of organic substance in supercritical carbon dioxide (SCCO2) as well as in its direct vicinity. We constructed and tested a cylindrical high-pressure chamber and an experiment system with a high speed camera. The solute/solvent combination of DL-α-tocopherol/SCCO2 was applied using shadowgraph. The diffusion coefficients at temperatures of 40o C, 50o C and 60o C and pressures between 75 bar and 90 bar were calculated based on the displacement of the droplet contour in the captured images. The shearing interferometry with a Wollaston-prism was then applied not only for the combination of DL-α-tocopherol/SCCO2, but also for other substances in SCCO2, for example for a type of rose oil and lubricant oil as well as for acetone, benzene, toluene and naphthalene. The changes of the refractive index gradient were directly measured and evaluated with the interferograms; afterwards changes of the density gradients and the diffusion coefficients were determined. We propose then a multivariate regression model to capture the relationship between the diffusion coefficient, the pressure and the temperature. To minimize the influence of gravity-driven convections in the solvent during diffusion, the experiments were also carried out under microgravity condition, i.e. in two parabolic flight campaign
UnivIS-Import:2018-02-22:Pub.2017.tech.ITC.stmmec.studyo

Study of turbulence induced orbital angular momentum channel crosstalk in a 1.6km free-space optical link - Lavery, Martin P.J.; Heim, Bettina; Peuntinger, Christian; Magaña-Loaiza, Omar S.; Karimi, Ebrahim; Bauer, Thomas; Banzer, Peter; Marquardt, Christoph; Willner, Alan E.; Boyd, Robert W.; Padgett, Miles J.; Leuchs, Gerd (CLEO: Science and Innovations, CLEO-SI 2015, 2015)
We experimentally study the turbulence induced crosstalk between orbital angular momentum channels transmitted over a 1.6 km optical link. Our presented results indicate that turbulence mitigation techniques will be required for links of this length. © OSA 2015.
CRIS-Team Scopus Importer:2022-06-05

Stylus ion trap for enhanced access and sensing - Leuchs, Gerd; et al. (Nature Physics, 2009)
Small, controllable, highly accessible quantum systems can serve as probes at the single-quantum level to study a number of physical effects, for example in quantum optics or for electric- and magnetic-field sensing. The applicability of trapped atomic ions as probes is highly dependent on the measurement situation at hand and thus calls for specialized traps. Previous approaches for ion traps with enhanced optical access included traps consisting of a single ring electrode or two opposing endcap electrodes. Other possibilities are planar trap geometries, which have been investigated for Penning traps and radiofrequency trap arrays. By not having the electrodes lie in a common plane, the optical access can be substantially increased. Here, we report the fabrication and experimental characterization of a novel radiofrequency ion trap geometry. It has a relatively simple structure and provides largely unrestricted optical and physical access to the ion, of up to 96% of the total 4 solid angle in one of the three traps tested. The trap might find applications in quantum optics and field sensing. As a force sensor, we estimate sensitivity to forces smaller than 1 yN Hz 1/2. © 2009 Macmillan Publishers Limited.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.stylus

Sub-40 fs pulses at 1.8 mu m and MHz repetition rates by chirp-assisted Raman scattering in hydrogen-filled hollow-core fiber - Loranger, Sebastien; Russell, Philip St. John; Novoa, David (Journal of the Optical Society of America B-Optical Physics, 2020)
The possibility to perform time-resolved spectroscopic studies in the molecular fingerprinting region or extending the cutoff wavelength of high-harmonic generation has recently boosted the development of efficient mid-infrared (mid-IR) ultrafast lasers. In particular, fiber lasers based on active media such as thulium or holmium are a very active area of research since they are robust, compact, and can operate at high repetition rates. These systems, however, are still complex, are unable to deliver pulses shorter than 100 fs, and are not yet as mature as their nearinfrared counterparts. Here, we report the generation of sub-40 fs pulses at 1.8 gm, with quantum efficiencies of 50% and without the need for post-compression, in hydrogen-filled, hollow-core photonic crystal fiber pumped by a commercial high-repetition-rate 300 fs fiber laser at 1030 nm. This is achieved by pressure-tuning the dispersion and avoiding Raman gain suppression by adjusting the chirp of the pump pulses and the proportion of higher-order modes launched into the fiber. The system is optimized using a physical model that incorporates the main linear and nonlinear contributions to the optical response. The approach is average power-scalable, permits adjustment of the pulse shape, and can potentially allow access to much longer wavelengths. (C) 2020 Optical Society of America
CRIS-Team WoS Importer:2021-01-08

Sub-Rayleigh quantum imaging using single-photon sources - Thiel, Christoph; Bastin, T.; von Zanthier, Joachim; Agarwal, G. S. (Physical Review A, 2009)
We propose a technique capable of imaging a distinct physical object with sub-Rayleigh resolution in an ordinary far-field imaging setup using single-photon sources and linear optical tools only. We exemplify our method for the case of a rectangular aperture and two or four single-photon emitters obtaining a resolution enhanced by a factor of 2 or 4, respectivel

Sub shot noise phase quadrature measurement of intense light beams - Leuchs, Gerd; et al. (Optics Letters, 2004)
We present a setup for performing sub-shot-noise measurements of the phase quadrature of intense pulsed light without the use of a separate local oscillator. A Mach-Zehnder interferometer with an unbalanced arm length is used to detect the fluctuations of the phase quadrature at a single sideband frequency. With this setup, the nonseparability of a pair of quadrature-entangled beams is demonstrated experimentally. © 2004 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.optik.1optik.subsho

Substrate-Induced Chirality in an Individual Nanostructure - Nechayev, Sergey; Barczyk, Rene; Mick, Uwe; Banzer, Peter (ACS Photonics, 2019)
We experimentally investigate the chiral optical response of an individual nanostructure consisting of three equally sized spherical nanoparticles made of different materials and arranged in 90 degrees bent geometry. Placing the nanostructure on a substrate converts its morphology from achiral to chiral. Chirality leads to pronounced differential extinction (circular dichroism) and optical rotation (circular birefringence), which would be strictly forbidden in the absence of a substrate or heterogeneity. This first experimental observation of the substrate-induced break of symmetry in an individual heterogeneous nanostructure sheds new light on chiral light-matter interactions at substrate-nanostructure interfaces.
CRIS-Team WoS Importer:2019-09-13

Substrate misorientation as additional parameter for low temperature growth of GaAs - Schür, Carsten; Marek, Tamas; Strunk, Horst Paul; Tautz, Sönke; Steen, Christian; Kiesel, Peter; Malzer, Stefan; Döhler, Gottfried; Niecke, M.; Schröder, F.; Mayer, R.; Knappe, R. (Physik mikrostrukturierter Halbleiter, 2001)
UnivIS-Import:2015-04-14:Pub.2001.tech.IW.LM.substr

Sub-THz and THz Photonic generation with continuous tunability using gain switching based optical frequency comb generators and n-i-p-n-i-p superlattice photomixers - de Dios, Christina; Criado, Ruben; Döhler, Gottfried; Preu, Sascha; Malzer, Stefan; Bauerschmidt, Sebastian; Garcia-Munoz, Enrique; Segovia-Vargas, Daniel; Acedo, Pablo (2012 IEEE International Topical Meeting on Microwave Photonics, MWP 2012, 2012)
In this work we present a compact and versatile way to generate sub-THz and THz signals using an OFCG based on a Photonic Local Oscillator responsible to generate the two wavelengths to be mixed in the photomixer based on a Gain Switching (GS) Scheme and the use of Phase Modulation; and n-i-p-n-i-p superlattice photomixers. The proposed scheme is able to cover a wide span with continuous tunability. The description of the different components of the system (Photonic Local Oscillator and Photomixer) is covered as well as some preliminary data. © 2012 IEEE.

Sub-two-cycle octave-spanning mid-infrared fiber laser - Huang, J.; Pang, M.; Jiang, X.; Köttig, F.; Schade, D.; He, W.; Butryn, M.; Russell, Philip St. John (Optica, 2020)
Compact and powerful ultrafast light sources at high pulse repetition rates, based on mode-locked near infrared fiber lasers, are now widely available and are being used in applications such as frequency metrology, molecular spectroscopy, and laser micro-machining. The realization of such lasers in the mid-infrared has, however, remained a challenge for many years. Here we report a record-breaking three-stage fiber laser system that uses an Er-doped fluoride fiber as gain medium, delivering W-level few-cycle pulses at 2.8 µm at a repetition rate of 42.1 MHz. A fiber-based seed oscillator, cavity dispersion-managed by a pulse-stretcher, generates near-100-fs mid-infrared pulses with >110 nm spectral bandwidth. These pulses are amplified to an average power of ∼1 W in a chirp-engineered fiber amplifier, and then compressed to ∼16 fs in a short length of highly nonlinear ZBLAN fiber, resulting in a more-than-octave-wide spectrum reaching from 1.8 µm to 3.8 µm with a total power of 430 mW.
CRIS-Team Scopus Importer:2020-07-03

SUCROSE TRANSPORTER 5 supplies Arabidopsis embryos with biotin and affects triacylglycerol accumulation - Pommerrenig, Benjamin; Popko, Jennifer; Heilmann, Martin; Schulmeister, Sylwia; Dietel, Katharina; Schmitt, Bianca; Stadler, Ruth; Feussner, Ivo; Sauer, Norbert (Plant Journal, 2013)
The Arabidopsis SUC5 protein represents a classical sucrose/H(+) symporter. Functional analyses previously revealed that SUC5 also transports biotin, an essential co-factor for fatty acid synthesis. However, evidence for a dual role in transport of the structurally unrelated compounds sucrose and biotin in plants was lacking. Here we show that SUC5 localizes to the plasma membrane, and that the SUC5 gene is expressed in developing embryos, confirming the role of the SUC5 protein as substrate carrier across apoplastic barriers in seeds. We show that transport of biotin but not of sucrose across these barriers is impaired in suc5 mutant embryos. In addition, we show that SUC5 is essential for the delivery of biotin into the embryo of biotin biosynthesis-defective mutants (bio1 and bio2). We compared embryo and seedling development as well as triacylglycerol accumulation and fatty acid composition in seeds of single mutants (suc5, bio1 or bio2), double mutants (suc5 bio1 and suc5 bio2) and wild-type plants. Although suc5 mutants were like the wild-type, bio1 and bio2 mutants showed developmental defects and reduced triacylglycerol contents. In suc5 bio1 and suc5 bio2 double mutants, developmental defects were severely increased and the triacylglycerol content was reduced to a greater extent in comparison to the single mutants. Supplementation with externally applied biotin helped to reduce symptoms in both single and double mutants, but the efficacy of supplementation was significantly lower in double than in single mutants, showing that transport of biotin into the embryo is lower in the absence of SUC5.

Superbunching and Nonclassicality as new Hallmarks of Superradiance - Bhatti, Daniel; von Zanthier, Joachim; Agarwal, Girish S. (Scientific Reports, 2015)
Superradiance, i.e., spontaneous emission of coherent radiation by an ensemble of two-level atoms in collective states introduced by Dicke in 1954, is one of the enigmatic problems of quantum optics. The startling gist is that even though the atoms have no dipole moment they radiate with increased intensity in particular directions. Following the advances in our understanding of superradiant emission by atoms in entangled W-states we examine the quantum statistical properties of superradiance. Such investigations require the system to have at least two excitations in order to explore the photon-photon correlations of the radiation emitted by such states. We present specifically results for the spatially resolved photon-photon correlations of systems prepared in doubly excited W-states and give conditions when the atomic system emits nonclassial light. Equally, we derive the conditions for the occurrence of bunching and even of superbunching, a rare phenomenon otherwise known only from nonclassical states of light like the squeezed vacuum. We finally investigate the photon-photon cross correlations of the spontaneously scattered light and highlight the nonclassicalty of such correlations. The theoretical findings can be implemented with current technology, e.g., using ions in a linear rf-trap, atoms in an optical lattice or quantum dots in a cavit

Superconducting circuits for quantum computing - Eichler, Christopher (QCHS SUMMER SCHOOL, 2022)
Keywords: wwwqudev

Superconducting Quantum Circuits - Eichler, Christopher (QSIT Meeting - Winter school, 2017)
Keywords: wwwqudev

Supercontinuum generation in ZBLAN glass photonic crystal fiber with six nanobore cores - Jiang, Xin; Joly, Nicolas; Finger, Martin A.; Babic, Fehim; Pang, Meng; Sopalla, Rafal; Frosz, Michael H.; Poulain, Samuel; Poulain, Marcel; Cardin, Vincent; Travers, John C.; Russell, Philip St. John (Optics Letters, 2016)
Photonic crystal fibers (PCFs) made from ZBLAN glass are of great interest for generating broadband supercontinua extending into the ultraviolet and mid-infrared regions. Precise sub-micrometer structuring makes it possible to adjust the modal dispersion over a wide range, making the generation of new frequencies more efficient. Here we report a novel ZBLAN PCF with six cores, each containing a central nanobore of a diameter similar to 330 nm. Each nanobore core supports several guided modes, and the presence of the nanobore significantly modifies the dispersion, strongly influencing the dynamics and the extent of supercontinuum generation. Spectral broadening is observed when a single core is pumped in the fundamental and first higher order core modes with 200 fs long pulses at a wavelength of 1042 nm. Frequency-resolved optical gating is used to characterize the output pulses when pumping in the lowest order mode. The results are verified by numerical simulations. (C) 2016 Optical Society of America

Supercontinuum Generation with Circularly Polarized Vortex Modes in a Chiral Three -Core PCF - Roth, Paul; Wong, Gordon K. L.; Frosz, Michael H.; Russell, Philip St. John (2020 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR), 2020)
CRIS-Team WoS Importer:2021-06-11

Superlinear threshold detectors in quantum cryptography - Lydersen, Lars; Jain, Nitin; Wittmann, Christoffer; Maroy, Oystein; Skaar, Johannes; Marquardt, Christoph; Makarov, Vadim; Leuchs, Gerd (Physical Review A - Atomic, Molecular, and Optical Physics, 2011)
We introduce the concept of a superlinear threshold detector, a detector that has a higher probability to detect multiple photons if it receives them simultaneously rather than at separate times. Highly superlinear threshold detectors in quantum key distribution systems allow eavesdropping the full secret key without being revealed. Here, we generalize the detector control attack, and analyze how it performs against quantum key distribution systems with moderately superlinear detectors. We quantify the superlinearity in superconducting single-photon detectors based on earlier published data, and gated avalanche photodiode detectors based on our own measurements. The analysis shows that quantum key distribution systems using detector(s) of either type can be vulnerable to eavesdropping. The avalanche photodiode detector becomes superlinear toward the end of the gate. For systems expecting substantial loss, or for systems not monitoring loss, this would allow eavesdropping using trigger pulses containing less than 120 photons per pulse. Such an attack would be virtually impossible to catch with an optical power meter at the receiver entrance. © 2011 American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

Superresolving Imaging of Arbitrary One-Dimensional Arrays of Thermal Light Sources Using Multiphoton Interference - Classen, Anton; Waldmann, Felix; Giebel, Sebastian; Schneider, Raimund; Bhatti, Daniel; Mehringer, Thomas; von Zanthier, Joachim (Physical Review Letters, 2016)
We propose to use multiphoton interferences of photons emitted fromstatistically independent thermal light sources in combination with linear optical detection techniques to reconstruct, i.e., image, arbitrary source geometries in one dimension with subclassical resolution. The scheme is an extension of earlier work [S. Oppel et al., Phys. Rev. Lett. 109, 233603 (2012)], where N regularly spaced sources in one dimension were imaged by use of the Nth-order intensity correlation function. Here, we generalize the scheme to reconstruct any number of independent thermal light sources at arbitrary separations in one dimension, exploiting intensity correlation functions of order m >= 3. We present experimental results confirming the imaging protocol and provide a rigorous mathematical proof for the obtained subclassical resolutio

Superresolving Multiphoton Interferences with Independent Light Sources - Oppel, Steffen; Büttner, Teresa; Kok, P.; von Zanthier, Joachim (Physical Review Letters, 2012)
We propose to use multiphoton interferences from statistically independent light sources in combination with linear optical detection techniques to enhance the resolution in imaging. Experimental results with up to five independent thermal light sources confirm this approach to improve the spatial resolution. Since no involved quantum state preparation or detection is required, the experiment can be considered an extension of the Hanbury Brown-Twiss experiment for spatial intensity correlations of order N > 2. DOI: 10.1103/PhysRevLett.109.2336

Suppression of Nonlinear Phase Noise in a DPSK Transmission Using a Nonlinear Amplifying Loop Mirror - Stephan, Christian; Sponsel, Klaus; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Optical Fiber Communication 2009, 2009)
Experimental and numerical investigations of phase-preserving amplitude regeneration in a DPSK transmission with a NALM have shown that a 3dB improvement of the Q-factor or alternatively a 3dB increase of fiber-launched power could be achieved. © 2009 IEEE.
UnivIS-Import:2017-12-18:Pub.2009.tech.IE.LEH.suppre

Suppression of the critical angle of diffraction in thin-film colloidal photonic crystals - Romanov, Sergei G.; Peschel, Ulf; Bardosova, Maria; Essig, Sabine; Busch, Kurt (Physical Review B, 2010)
We present an experimental and numerical investigation of the polarization anisotropy of the zero-order backdiffracted light from three-dimensional thin-film photonic crystals assembled from colloidal spheres. In particular, we compare simulations of reflectance spectra from perfectly ordered fcc lattice of spheres with measured reflectance data from self-organized opal films and forced-assembled Langmuir-Blodgett crystal films. We identify cross-polarization couplings and interactions between photonic crystal eigenmodes as the major physical mechanisms for resonance depolarization effects. Based on this, we find that a necessary condition for the observation of critical angles of diffraction in three-dimensional lattices is that the orientation of the light's plane of incidence coincides with a high-symmetry plane of the crystal lattice. We further show that for currently achievable colloidal photonic crystals with moderate refractive index contrast, this resonance depolarization mechanisms together with the destructive influence of lattice disorder effectively renders the meaning of a critical angle of diffraction obsolete.
EAM Import::2019-03-13

Surface structuring of β-TCP and transition to α-TCP induced by femtosecond laser processing - Aceti, D. M.; Filipov, E.; Sotelo, Lamborghini; Fontanot, T.; Christiansen, S.; Lasgorceix, M.; Leriche, A.; Buchvarov, I.; Daskalova, A. (Journal of Physics: Conference Series, 2023)
Tricalcium phosphate (Ca3(PO4)2, TCP), is one of the most studied and used as material for bioresorbable implants. The β phase has a slower dissolution dynamic and ensures mechanical support for a longer time in biological environment, while a faster release of ions characterize the α phase that trigger a stronger biological response. In this work a femtosecond laser system was used to process β-TCP pellets surface. The femtosecond laser processing results in surface morphology modification, by turning the flat mirror polished surface into a rough and opaque one. The morphological and phisycochemical characteristics of material surface were studied by means of SEM, AFM, Raman, XRD and contact angle measurement. The processed surface showed the formation of micro and nano roughness alongside, furthermore a partial phase transformation from β-TCP to α-TCP was detected. A significant improvement in surface wettability for three different liquids (i.e.water, ethylene glycol and diiodo-methane) is reported. This implies an increase in surface free energy as well. The combination of α and β phase, together with the increased roughness obtained by laser processing, could positively affect the cell adhesion and metabolic activity.
CRIS-Team Scopus Importer:2023-06-02

Sustained Self-Starting Orbital Motion of a Glass-Fiber "nanoengine" Driven by Photophoretic Forces - Xie, Shangran; Pennetta, Riccardo; Wang, Zheqi; Russell, Philip St. John (ACS Photonics, 2019)
Controllable optically driven rotation of microscopic objects is desirable in many applications, but is difficult to achieve. Here we report a sustained self-starting orbital motion of a clamped elongated nanostructure, a glass-fiber nanospike, when a CW laser beam is focused axially onto its tip. Analysis shows that photophoretic antitrapping forces, acting on the nanospike with a delayed response, introduce optomechanical gain into the mechanical motion, overcoming the intrinsic mechanical dissipation and resulting in growth from noise of oscillations at the resonant frequency of the nanospike. These photophoretic forces further enable phase-locking of the orthogonal fast and slow vibrations of the nanospike (induced by slight mechanical anisotropy), giving rise to a self-sustained orbital motion. The locked phase of orbital motion can be changed by tuning the gas pressure and adjusting the geometrical asymmetry of the system. This light-driven nanoengine opens up a new degree of freedom for controlling the rotational motion of elongated nano-objects.
CRIS-Team Scopus Importer:2019-12-20
Keywords: fiber nanospike; nanomotor; optomechanics; orbital motion; photophoretic force

Synchronization of gigahertz core resonances in multiple photonic crystal fiber cores by timing-modulated harmonic mode locking - Yeh, Dung-Han; He, Wenbin; Pang, Meng; Jiang, Xin; Russell, Philip St J. (Optica, 2021)
Synchronization of mechanical oscillators by optical forces is a topic that has been much explored in recent years, for example, in the context of SiN microdisk resonators. Here we report stable long-termsynchronization of the core vibrations of three different photonic crystal fibers, driven intra-cavity by a 2 GHz train of timing-modulated pulses in a high harmonic opto-acoustically mode-locked fiber laser. The core resonances are equally spaced in frequency and are coupled purely by the optical field. Under the correct conditions, they become stably synchronized, being simultaneously driven by the timing-modulated pulse train. Floquet-Bloch theory, in which the pulses are treated as particles trapped in potential wells and coupled by optomechanical back-action, describes the complex temporal dynamics observed in the experiments. This unique system provides a novel means of modifying the temporal structure of pulse trains running at few-gigahertz repetition rates. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
CRIS-Team WoS Importer:2021-12-31

Synthesis and dissociation of soliton molecules in parallel optical-soliton reactors - He, Wenbin; Pang, Meng; Yeh, Dung-Han; Huang, Jiapeng; Russell, Philip St. John (Light: Science & Applications, 2021)
Mode-locked lasers have been widely used to explore interactions between optical solitons, including bound-soliton states that may be regarded as “photonic molecules”. Conventional mode-locked lasers normally, however, host at most only a few solitons, which means that stochastic behaviours involving large numbers of solitons cannot easily be studied under controlled experimental conditions. Here we report the use of an optoacoustically mode-locked fibre laser to create hundreds of temporal traps or “reactors” in parallel, within each of which multiple solitons can be isolated and controlled both globally and individually using all-optical methods. We achieve on-demand synthesis and dissociation of soliton molecules within these reactors, in this way unfolding a novel panorama of diverse dynamics in which the statistics of multi-soliton interactions can be studied. The results are of crucial importance in understanding dynamical soliton interactions and may motivate potential applications for all-optical control of ultrafast light fields in optical resonators.
CRIS-Team Scopus Importer:2021-06-18

Synthetic Image Rendering Solves Annotation Problem in Deep Learning Nanoparticle Segmentation - Mill, Leonid; Wolff, David; Gerrits, Nele; Philipp, Patrick; Kling, Lasse; Vollnhals, Florian; Ignatenko, Andrew; Jaremenko, Christian; Huang, Yixing; De Castro, Olivier; Audinot, Jean Nicolas; Nelissen, Inge; et al. (Small Methods, 2021)
Nanoparticles occur in various environments as a consequence of man-made processes, which raises concerns about their impact on the environment and human health. To allow for proper risk assessment, a precise and statistically relevant analysis of particle characteristics (such as size, shape, and composition) is required that would greatly benefit from automated image analysis procedures. While deep learning shows impressive results in object detection tasks, its applicability is limited by the amount of representative, experimentally collected and manually annotated training data. Here, an elegant, flexible, and versatile method to bypass this costly and tedious data acquisition process is presented. It shows that using a rendering software allows to generate realistic, synthetic training data to train a state-of-the art deep neural network. Using this approach, a segmentation accuracy can be derived that is comparable to man-made annotations for toxicologically relevant metal-oxide nanoparticle ensembles which were chosen as examples. The presented study paves the way toward the use of deep learning for automated, high-throughput particle detection in a variety of imaging techniques such as in microscopies and spectroscopies, for a wide range of applications, including the detection of micro- and nanoplastic particles in water and tissue samples.
CRIS-Team Scopus Importer:2021-05-14
Keywords: helium ion microscopy; image analysis; machine learning; nanoparticles; segmentation; toxicology

Systematic investigation of the effect of aberration on ultrashort optical pulses focused by an aplanatic lens - Fries, Sebastian; Loosen, Florian; Lindlein, Norbert (Proceeding, 5th doctoral students conference on optics (DoKDoK), 2016)

Systematic investigation of the principal and first secondary maxima of ultrashort optical pulses focused by a high numerical aperture aplanatic lens - Lindlein, Norbert; Loosen, Florian; Fries, Sebastian (Optical Systems Design 2015: Computational Optics, 2015)
The electromagnetic field in the focus of an ideal aplanatic lens with high numerical aperture, which is illuminated by an ultrashort optical pulse and plane wave front, is simulated by taking the vectorial Debye integral and the coherent superposition of a frequency spectrum of monochromatic waves. The behavior of the principal maxima and the first secondary maxima as function of the numerical aperture (NA) and the pulse duration T is investigated systematically for light incident with linear polarization. First, one would not expect remarkable deviations from the stationary case. But also this simple system of an ideal aplanatic lens without any chromatic or monochromatic aberrations (of course only simple from the point of theory, but not at all from the point of practical realization) shows some remarkable results. If the NA (in vacuum) tends to the limiting case of 1.0 the maximum value of |E| increases faster than expected from the scalar theory (Airy disc) with a maximum deviation of about 13%. The second effect really comes from very short pulses, i.e. very small values T. Then, the value of |E| compared to the expected linear increase with 1/T decreases slightly (only less than 2%), but systematically for all NAs. Even more interesting is the dependence of the height of the first secondary maxima along the x-axis and y-axis on the NA and 1/T. It can be seen that along both axes the first secondary maxima nearly vanish for very short pulses, i.e. large values 1/T.
Keywords: aplanatic lens; electric field distribution in the focus; focusing at high numerical aperture; optical simulation techniques; propagation of ultrashort optical pulses; Ultrashort optical pulses

Tackling Africa's digital divide 706 639/624/1075/187 comment - Lavery, Martin P. J.; Abadi, Mojtaba Mansour; Bauer, Ralf; Brambilla, Gilberto; Cheng, Ling; Cox, Mitchell A.; Dudley, Angela; Ellis, Andrew D.; Fontaine, Nicolas K.; Kelly, Anthony E.; Marquardt, Christoph; Matlhane, Selaelo; et al. (Nature Photonics, 2018)
CRIS-Team Scopus Importer:2022-06-05

Tailored polarization patterns for performance optimization of optical devices - Leuchs, Gerd; et al. (Journal of Modern Optics, 2006)
In the case of strong focusing the smallest possible focal spot can be reached, provided one uses a specially designed polarization pattern. Other optical set-ups also employing high numerical aperture imaging are likewise expected to improve performance under polarization optimization. We propose a strategy for calculating the polarization pattern required for system optimization. A single element modulating only the polarization and not amplitude and phase may lead to satisfactory performance in some cases.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.tailor

TE- and TM-polarization-resolved spectroscopy on quantum wells under normal incidence - Malzer, Stefan; Leuchs, Gerd; Schardt, Michael; et al. (Physica E-Low-Dimensional Systems & Nanostructures, 2006)
We present TE- and TM-polarization-resolved photocurrent measurements on quantum well pin diodes under normal incidence. Usually, optical experiments performed in such a geometry yield information only about transitions involving in-plane (p and p ) components of the hole wave functions because of the in-plane (TE) polarization of the light. Information on transitions sensitive to the p components can be obtained by focussing a radially polarized laser beam through a microscope objective with high numerical aperture ( NA = 0.9). With our setup, the electrical field vector at the focal tail has a significant component along the optical axis (TM-polarization!) which enables excitation of transitions sensitive to p components also. Additionally, the existence of a degenerate (azimuthally polarized) optical mode enables switching these p components on and off easily. Experimental evidence of these features has been achieved by exploiting the selection rules for e-hh and e-lh transitions in a quantum well structure. We present a comparison of our recorded spectra with theoretical predictions obtained from simple geometric optics assumptions. For our quantum wells the polarization effects are small because our measurement averages the intensity distribution of the whole focal plane. We plan to extend our measurements to polarization resolved single quantum dot spectroscopy. By restricting the detection region to the spatial extent of a single dot, one can exploit the almost pure TM-polarization on the optical axis for obtaining high contrast between heavy- and light-hole exciton absorption. © 2006.

Technical Modelling Approach for Spatial Integrated Optomechatronic Products - Zeitler, Jochen Tobias; Reitberger, Thomas; Reichle, Andreas; Backhaus, Carsten; Lindlein, Norbert; Franke, Jörg (Procedia CIRP, Volume 84, 2019)
In the age of digitalization, the amount of data generated and transferred continues to increase dramatically. To increase the usability of this data it must be accessible with sufficient transmission bandwidth. Optical signals are already being used for transmitting data over long distances and high bandwidths, as this enables fast and low-loss data transmission. This trend is now also continuing in smaller scales of data transmission. Consequently, even highly integrated electrical circuits must be supported with optical components. Therefore, completely new research approaches for the product development of spatially integrated optical waveguides are necessary. The polymer-based aerosol jet printing represents a promising method to print optical waveguides on 3D circuit carriers. For this reason, the Research Group for Module Integrated Bus Systems deals with topics related to product development and production of such systems. A focus is to customize the design and associated modelling tasks accordingly. Thus, it is essential to create methodical approaches for a digital representation of waveguides and their production processes in order to map the physical behavior and to predict their manufacturability. Current studies show that integrated engineering approaches with removed boundaries among engineering domains are preferable to traditional engineering approaches. Consequently, novel engineering tools are needed for modelling the geometric as well as the physical properties of optical waveguides with the possibility to integrate specific design rule checks. The presented modelling approach in this paper provides/supports the creation of exact digital models without discontinuities through unnecessary interfaces. This article presents a method for a powerful computer-aided modelling environment that enables the design of models that are capable of representing and validating logical relationships among optoelectronic networks, but also considers challenges resulting from spatial geometric characteristics as well as restrictions from manufacturing and physic
Keywords: Computer aided design (CAD); Product development; Optomechatronics

Telecentric line scanning system based on a ring surface mirror for inline processes - Loosen, Florian; Lindlein, Norbert; Donner, Klaus (Advanced Optical Technologies, 2016)
In many industrial applications, an inline measurement of a production process poses a difficult challenge for any optical system. Therefore, telecentric optical systems are being used to ensure an independence of the magnification of the object from the working distance. Usually, telecentric optical systems are impractical for inline applications with large objects due to the size of the telecentric optical system, which has to be larger than the object. Therefore, a new approach of telecentric line scanning systems was developed to gain access to this advantage.
Keywords: industrial applications; inline processes; measuring system; optical design and simulation; ring surface mirror; telecentric system.

Telecom Compatible Quantum Key Distribution - Learning from Classical Coherent Communication - Marquardt, Christoph (2019 Optical Fiber Communications Conference and Exhibition, OFC 2019 - Proceedings, 2019)
Quantum key distribution (QKD) enables secure cryptography that is safe against future attacks by quantum computers. We show recent advances in continuous variable QKD and highlight similarities and differences to classical coherent communication.
CRIS-Team Scopus Importer:2019-05-21

Telezentrischer Linienscanner auf Basis eines Ringfächenspiegels zur Oberflächenanalyse von Bauteilen - Loosen, Florian; Iff, Wolfgang; Lindlein, Norbert; Donner, Klaus (Proceeding, 115. Jahrestagung der DGaO, 2014)
Telezentrische Objektive finden heutzutage in der Messtechnik Anwendung, damit auch bei Veränderung des Objektabstands der Abbildungsmaßstab des Systems nicht von der Tiefe des Objekts abhängt. Da jedoch telezentrische Objektive für das Abscannen großer Oberflächen zu groß und preisintensiv sind, wird hier für diese Anwendung ein modulares System vorgestellt, mit dessen Aufbau ein Objekt linienförmig abgescannt werden kann. Das Ziel dieser Arbeit ist, eine ringförmige Scanlinie auf eine Zeilenkamera abzubilden. Dabei werden die von jedem Objektpunkt ausgehenden Hauptstrahlen durch einen Ringflächenspiegel um 90° abgelenkt und das Objekt auf eine Kugelschale projiziert. Abhängig von der Geometrie der spiegelnden Fläche entsteht so ein reelles oder virtuelles Zwischenbild des Objekts, welches durch ein Abbildungssystem auf den Detektor abgebildet wird. Durch die optische Simulation der Systembestandteile sowie des Gesamtsystems können verschiedene Einflussgrößen genau bestimmt werden. Zur Analyse werden dafür die Punktbildfunktion (PSF) in lateraler sowie in axialer Richtung (Schärfentiefe im Objektraum) und die Wellenaberrationen (WA) der Strahlenbündel bestimmt.

Temporally Distilled High-Dimensional Biphotonic States from Thin Sources - Sultanov, Vitaliy; Chekhova, Maria (ACS Photonics, 2024)
Generation of entangled photons through spontaneous parametric down-conversion (SPDC) from micro- and nanoscale sources offers unprecedented freedom in quantum state engineering, including the ability to generate two-photon states with high-dimensional hyperentanglement. However, as the source of SPDC gets smaller, the role of photoluminescence increases, which leads to the contamination of two-photon states with a thermal background. Here we propose and implement a solution to this problem: by using pulsed SPDC and time distillation, we increase the purity and the heralding efficiency of the photon pairs. In the experiment, we increased the purity of the two-photon states generated in a 7 μm film of lithium niobate from 0.002 to 0.99. With the higher purity we were able to observe and characterize different polarization states of photon pairs generated simultaneously due to relaxed phase matching. In particular, we showed the presence of orthogonally polarized photons that are potentially usable for the generation of polarization entanglement.
CRIS-Team Scopus Importer:2024-02-09
Keywords: distillation; nanoscale; photon pairs; purity

Temporal shaping of heralded photons in a resonator-assisted parametric down-conversion with modulated pump pulses - Averchenko, V. A.; Förtsch, M.; Fischer, M.; Aiello, A.; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2015)
CRIS-Team Scopus Importer:2022-06-05

Temporal shaping of single photons enabled by entanglement - Averchenko, Valentin; Sych, Denis; Schunk, Gerhard; Vogl, Ulrich; Marquardt, Christoph; Leuchs, Gerd (Physical Review A, 2017)
We present a method to produce pure single photons with an arbitrary designed temporal shape in a heralded way. As an indispensable resource, the method uses pairs of time-energy entangled photons. One photon of a pair undergoes temporal amplitude-phase modulation according to the desired shape. Subsequent frequency-resolved detection of the modulated photon heralds its entangled counterpart in a pure quantum state. The temporal shape of the heralded photon is indirectly affected by the modulation in the heralding arm. We derive conditions for which the shape of the heralded photon is given by the modulation function. The method can be implemented with various sources of time-energy entangled photons. In particular, using entangled photons from parametric down-conversion the method provides a simple means to generate pure shaped photons with an unprecedented broad range of temporal durations, from tenths of femtoseconds to microseconds. This shaping of single photons will push forward the implementation of scalable multidimensional quantum information protocols, efficient photon-matter coupling, and quantum control at the level of single quanta.
CRIS-Team Scopus Importer:2022-06-05

Testing acylindrical microlenses at grazing incidence - Lindlein, Norbert; et al. (Optik, 2000)
An interferometer is described which allows the fast test of acylindrical microlenses at grazing incidence. The interferometer uses two diffractive optical elements as beam splitters and beam shapers. For the test of cylinder lenses at grazing incidence a conical test wavefront is needed, which is generated by diffraction at a phase structure. One main feature is that the sensitivity only depends on the pitch of the diffractive elements. The interferometer, the fringe evaluation method, and the method to eliminate aberrations are described in detail and measurement results are presented.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.optik.1optik.testin

Test of a remote sensing Michelson-interferometer for temperature Measurements in the Mesosphere on a REXUS Rocket - Deiml, Michael; Song, Rui; Fröhlich, Denis; Rottland, Björn; Wagner, Fritz; Liu, Jilin; Wroblowski, Oliver; Chen, Qiuyu; Loosen, Florian; Kaufmann, Martin; Rongen, Heinz; Neubert, Tom; et al. (23. ESA Symposium on European Rocket and Ballon Programmes and related Research, 2017)
The experiment AtmoHIT, the Atmospheric Heterodyne Interferometer Test, is a precursor mission with the goal to verify a small satellite remote sensing instrument under space conditions. The satellite instrument is developed to measure temperatures in the Mesosphere/Lower-Thermosphere. Temperature measurements allow the characterization of gravity waves, which have an increasing importance in the modelling of the climate system representing one of the larger uncertanties in this field. The instrument consists of a highly miniturized and rigid Spatial Heterodyne Spectrometer (SHS), which measures the oxygen atmospheric band emission in the Mesosphere. The instrument resolves individual rotational lines whose intensities follow a Boltzmann law allowing for the derivation of temperature from the relative structure of these lines. This instrument ich characterized by its high throughput at a small form factor to perform scientific remote sensing measurements with a CubeSat. The AtmoHIT experiment is part of the Rocket Experiment for University Students campaign (REXUS 22), realised under a bilateral Agency Agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB). This contribution focuses on the developed technologies, laboratory measurements and rocket campaign results.

The Asymmetric Fiber Sagnac Interferometer as a Possibility of Noise-Reduction and Puls-Shaping in Modern High Bitrate Telecommunication Systems - Wietfeld, André; Meißner, Markus; Schmauß, Bernhard; Korolkova, Natalia; Leuchs, Gerd (DPG-Frühjahrstagung, 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.IE.LEH.theasy

The asymmetric fiber-Sagnac interferometer in a high bitrate telecommunication system - Leuchs, Gerd; et al. (CLEO/Europe Focus Meeting Conference Digest, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.optik.1optik.theasy

The deep space quantum link: prospective fundamental physics experiments using long-baseline quantum optics - Mohageg, Makan; Mazzarella, Luca; Anastopoulos, Charis; Gallicchio, Jason; Hu, Bei-Lok; Jennewein, Thomas; Johnson, Spencer; Lin, Shih-Yuin; Ling, Alexander; Marquardt, Christoph; Meister, Matthias; Newell, Raymond; et al. (EPJ Quantum Technology, 2022)
The National Aeronautics and Space Administration’s Deep Space Quantum Link mission concept enables a unique set of science experiments by establishing robust quantum optical links across extremely long baselines. Potential mission configurations include establishing a quantum link between the Lunar Gateway moon-orbiting space station and nodes on or near the Earth. This publication summarizes the principal experimental goals of the Deep Space Quantum Link. These goals, identified through a multi-year design study conducted by the authors, include long-range teleportation, tests of gravitational coupling to quantum states, and advanced tests of quantum nonlocality.
CRIS-Team Scopus Importer:2023-04-20
Keywords: Foundational quantum mechanics; General relativity; Quantum optics

The Direct Writing of Plasmonic Gold Nanostructures by Electron-Beam-Induced Deposition - Hoeflich, Katja; Yang, Ren Bin; Berger, Andreas; Leuchs, Gerd; Christiansen, Silke (Advanced Materials, 2011)
Various nanostructures are directly written by electron-beam-induced deposition using dimethyl-gold(III)-acetylacetonate as the precursor gas. After purification, their potential applications include plasmonic devices and metamaterials. Carbon contamination of the as-written structures can be completely removed by low-temperature ozone treatment, leaving polycrystalline pure gold structures (see figure). This treatment reduces the size of the nanostructures but does not substantially alter their functional shape.
EAM Import::2019-03-12

The Effect of Dissipation on Nonclassical States of the Radiation Field - Leuchs, Gerd; et al. (Laser Physics, 2005)
We point out similarities in the evolution of different types of nonclassical light fields. Generally, Fock and cat states are considered to decay much faster under dissipation than do squeezed states. We connect measurements of the intensity correlation function of nonclassical light to the second moment of the photon number distribution function. It is shown that all these nonclassical fields behave in a similar manner when one is looking at an appropriate property. Finally it is shown how the electronic-detection noise floor, typically present in measurements of the variance of a photocurrent, can be eliminated based upon a procedure that is well-established for intensity correlation measurements. Copyright © 2005 by MAIK "Nauka/ Interperiodica" (Russia).
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.optik.1optik.theeff

The effect of the high surface roughness in a comparative process - Häusler, Gerd; et al. (Optics and Lasers in Engineering, 2002)
Comparative measurement methods are used to compare the behaviour of two macroscopically identical but microscopically different object surfaces. The roughness of these surfaces can have any value. The aim of this paper is to demonstrate theoretically as well as experimentally, the effect and the limitations of the high surface roughness on the visibility of the difference correlation fringes obtained in comparative processes. © 2001 Elsevier Science Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.optik.1optik.theeff
Keywords: Comparative holography; Difference correlation fringes; Surface roughness; Visibility

The focus of light-linear polarization breaks the rotational symmetry of the focal spot - Leuchs, Gerd; et al. (Journal of Modern Optics, 2003)
We experimentally demonstrate for the first time that a linearly polarized beam is focused to an asymmetric spot when using a high-numerical aperture focusing system. This asymmetry was predicted by Richards and Wolf in 1959 and can only be measured when a polarization-insensitive sensor is placed in the focal region. We used a specially modified photodiode in a knife-edge-type set-up to obtain highly resolved images of the total electric energy density distribution at the focus. The results are in good agreement with the predictions of a vectorial focusing theory.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.thefoc

The focus of light - theoretical calculation and experimental tomographic reconstruction - Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 2001)
We present numerical calculations on the field distribution in the focus of an optical system with high numerical aperture. The diffraction integrals which are based on the Debye approximation are derived and evaluated for a radially polarized input field with a doughnut-shaped intensity distribution. It is shown that this mode focusses down to a spot size significantly smaller as compared to the case of linear polarization. An experimental setup to measure the three-dimensional intensity distribution in the focal region is presented, which is based on the knife-edge method and on tomographic reconstruction.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.thefoc

The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone - Milovanovic, Petar; Zimmermann, Elizabeth A.; Scheidt, Annika Vom; Hoffmann, Björn; Sarau, George; Yorgan, Timur; Schweizer, Michaela; Amling, Michael; Christiansen, Silke; Busse, Bjoern (Small, 2017)
Osteocytes—the central regulators of bone remodeling—are enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacuno-canalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of high-resolution imaging and physics-based techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals.
Keywords: biomineralization; bone cells; lacuno-canalicular network; nanospherites; osteocytes

The Optical Kerr Effect and Quantum Optics in Fibres - Leuchs, Gerd; et al. (Progress in Optics, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.optik.1optik.theopt

Theoretical description of a method for simultaneous measurement of phase and arbitrary polarization - Kellermann, Christine; Rothau, Sergej; Lindlein, Norbert (116. Jahrestagung der DGaO, 2015)

Theoretical-experimental study of the vectorial modal properties of polarization-stable multimode grating VCSELs - Debernardi, Pierluigi; Ostermann, Johannes-Michael; Sondermann, Markus; Ackemann, Thorsten; Bava, Gian Paolo; Michalzik, Rainer (IEEE Journal of Selected Topics in Quantum Electronics, 2007)
Vertical-cavity surface-emitting lasers (VCSELs) with a monolithically integrated grating in the outcoupling aperture have proven to generate a stable and predictable polarization of the emitted light. This paper provides further insight into the polarization anisotropies of grating-controlled highly multimode VCSELs by direct experimental measurements of crucial vectorial characteristics, i.e., modal dichroism and birefringence. This is achieved by a careful analysis of linewidths and peak positions of the dominant and the suppressed polarizations of the emission spectra recorded close to threshold. These experimental results allow us for the first time to compare the observed dichroism and birefringence directly with simulations performed with a fully vectorial, three-dimensional model. Large dichroisms exceeding 30 GHz, even for higher transverse modes, were found to agree very well with the simulations. Such high dichroisms clearly indicate the excellent capability of integrated surface gratings for reliable polarization control, even under extreme operation conditions. © 2007 IEEE.
Keywords: Electromagnetic modeling; Polarization control; Semiconductor laser; Surface grating; Vertical-cavity surface-emitting laser (VCSEL)

The phase shift induced by a single atom in free space - Sondermann, Markus; Leuchs, Gerd (Journal of the European Optical Society, 2013)
In this article we theoretically study the phase shift a single atom imprints onto a coherent state light beam in free space. The calculations are performed in a semiclassical framework. The key parameters governing the interaction and thus the measurable phase shift are the solid angle from which the light is focused onto the atom and the overlap of the incident radiation with the atomic dipole radiation pattern. The analysis includes saturation effects and discusses the associated Kerr-type non-linearity of a single atom.
Keywords: Atom-photon interaction; Free space; Kerr effect; Phase shift

The photonic wheel - demonstration of a state of light with purely transverse angular momentum - Banzer, Peter; Neugebauer, Martin; Aiello, Andrea; Marquardt, Christoph; Lindlein, Norbert; Bauer, Thomas; Leuchs, Gerd (Journal of the European Optical Society: Rapid Publications, 2013)

The polarization properties of a tilted polarizer - Korger, Jan; Kolb, Tobias; Banzer, Peter; Aiello, Andrea; Wittmann, Christoffer; Marquardt, Christoph; Leuchs, Gerd (Optics Express, 2013)
Polarizers are key components in optical science and technology. Thus, understanding the action of a polarizer beyond oversimplifying approximations is crucial. In this work, we study the interaction of a polarizing interface with an obliquely incident wave experimentally. To this end, a set of Mueller matrices is acquired employing a novel procedure robust against experimental imperfections. We connect our observation to a geometric model, useful to predict the effect of polarizers on complex light fields. © 2013 Optical Society of America.
CRIS-Team Scopus Importer:2022-06-05

The quantum properties of multimode optical amplifiers revisited - Leuchs, Gerd; et al. (Advances in Atomic Molecular and Optical Physics, 2006)
There are a number of physically different realizations of an optical amplifier and yet they all share the same fundamental quantum limit as far as their noise characteristics are concerned. We review the underlying mathematical formalism without the restriction of a minimum number of modes being involved, its physical implications and relate it to the phenomenological models for the various amplifiers. © 2006 Elsevier Inc. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.thequa

Thermal origin of light emission in nonresonant and resonant nanojunctions - Ott, Christian; Götzinger, Stephan; Weber, Heiko B. (Physical Review Research, 2020)
Electron tunneling is associated with light emission. In order to elucidate its generating mechanism, we provide an experimental ansatz that employs fixed-distance epitaxial graphene as metallic electrodes. In contrast to previous experiments, this open geometry permits an unobscured light spread from the tunnel junction, enabling both a reliable calibration of the visible to infrared emission spectrum and a detailed analysis of the dependence of the parameters involved. In a nonresonant geometry, the emitted light is perfectly characterized by a Planck spectrum. In an electromagnetically resonant environment, resonant radiation is added to the thermal spectrum, both being strictly proportional in intensity. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. In a long-running discussion whether the light is of thermal or electromagnetic origin, these results on graphene nanojunctions clearly favor the thermal pictur

Thermodynamic Control of Nanoliter Volumes of CS2 via Stimulated Brillouin Scattering - Geilen, Andreas; Popp, Alexandra; Das, Debayan; Junaid, Saher; Poulton, Christopher; Chemnitz, Mario; Marquardt, Christoph; Schmidt, M. A.; Stiller, Birgit (Optics InfoBase Conference Papers, 2022)
We present Brillouin-Mandelstam measurements of hard-to-reach, thermodynamic regimes in fully-sealed, CS2-filled liquid-core optical fibers. We investigate the Brillouin response in the positive and negative pressure regimes for isochoric and isobaric processes.
CRIS-Team Scopus Importer:2023-04-20

The role of coherence in mode bistability of gas laser in inhomogenous medium - Leuchs, Gerd; et al. (Journal of Modern Optics, 2001)
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.therol

The standard quantum limit of coherent beam combining - Müller, Christian; Sedlmeir, F.; Martynov, V. O.; Marquardt, Christoph; Andrianov, A. V.; Leuchs, Gerd (New Journal of Physics, 2019)
Coherent beam combining refers to the process of generating a bright output beam by merging independent input beams of individually diffusing relative phases by locking them to each other. We report the first quantum mechanical noise limit calculations for coherent beam combining and compare our results to quantum-limited amplification. Our coherent beam combining scheme is based on an optical Fourier transformation which renders the scheme compatible with integrated optics combined with feed-back stabilization of the relative phases. The scheme can belayed out for an arbitrary number of input beams and approaches the shot noise limit for a large number of inputs.
CRIS-Team WoS Importer:2019-10-15

The Wigner flow on the sphere - Yang, Popo; Valtierra, Ivan F.; Klimov, Andrei B.; Wu, Shin-Tza; Lee, Ray-Kuang; Sanchez-Soto, Luis L.; Leuchs, Gerd (Physica Scripta, 2019)
We derive a continuity equation for the evolution of the SU(2) Wigner function under nonlinear Kerr evolution. We give explicit expressions for the resulting quantum Wigner current, and discuss the appearance of the classical limit. We show that the global structure of the quantum current significantly differs from the classical one, which is clearly reflected in the form of the corresponding stagnation lines.
CRIS-Team Scopus Importer:2019-05-07
Keywords: phase space; Wigner flow; Wigner function

Thio-oxalic Acid 2-Amide-1-hydrazide-2-hydrazone - Heinemann, Frank Wilhelm; Hartung, H; Dehne, Henry; Scheunemann, A. (Acta crystallographica. Section C, Crystal structure communications, 1995)

Three-dimensional angstrom resolution in fluorescence microscopy: Insight into protein structure - Boening, Daniel; Weisenburger, Siegfried; Schomburg, Benjamin; Giller, Karin; Becker, Stefan; Griesinger, Christian; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2017)
CRIS-Team Scopus Importer:2023-03-27

Three-dimensional photonic crystals with an active surface: Gold film terminated opals - Ding, Boyang; Pemble, Martyn E.; Korovin, Alexander V.; Peschel, Ulf; Romanov, Sergey (Physical Review B, 2010)
A hybrid metal-dielectric photonic crystal, a thin opal slab coated by a gold film, has been designed in order to exercise additional control upon the light propagation in a photonic band-gap material using extraordinary optical transmission in the corrugated gold film. The photonic and plasmonic components of the hybrid crystal are closely linked, because the photonic crystal lattice provides a spatial template for the gold film corrugation and modifies the electromagnetic vacuum in the vicinity of the gold film. Due to coupling of light diffracted in the opal lattice to surface plasmon polaritons in the metal film, the spectra and angle diagrams of transmission in hybrid structures deviate from the linear superposition of transmission functions of both hybrid components. In particular, the selective conversion of diffraction minima, and cavity mode and thickness dependence of the surface plasmon polariton-related properties have been observed. The synergy of three resonance mechanisms behind the functionality of hybrid photonic crystals provides a uniquely broad tunability of their optical properties.
EAM Import::2019-03-12

Three-Dimensional Sensors - Potentials and Limitations - Häusler, Gerd (Handbook of Computer Vision and Applications, Vol. 1: Sensors and Imaging, 1999)
UnivIS-Import:2015-04-20:Pub.1999.nat.dphy.optik.1optik.threed

THz-photomixer based on quasi-ballistic transport - Döhler, Gottfried; Renner, Frank; Klar, Oliver; Eckardt, Martin; Schwanhäußer, Axel; Malzer, Stefan; Driscoll, Dan; Hanson, Micah; Gossard, Art; Loata, gabriel; Löffler, Torsten; Roskos, Hartmut (Semiconductor Science and Technology, 2005)
We report on a novel concept for THz photomixers with high conversion efficiency up to several THz. In contrast to the conventional pin photomixer we can overcome the trade-off between either optimizing transit-time or RC-roll-off. Using quasi-ballistic transport in nano-pin-diodes the transport path can be optimized regarding both path length and transit time. Independently, the capacitance can be kept small by using a sufficiently large number of optimized nano-pin-diodes in series. The concept is presented in detail and first experimental results are reported which corroborate our theoretical expectations. © 2005 IOP Publishing Ltd.

Time evolution of a quantum soliton in a Kerr medium - Leuchs, Gerd; et al. (Journal of Modern Optics, 2001)
The Q-function of the quantum soliton in a fibre is derived in a new form suitable for the assessment of the possibilities for experimental observations of specific quantum-soliton effects. The characteristic effects of soliton evolution are associated with a cubic term in the nonlinear phase angle and appear at distances well beyond the attenuation length (long range). At the accessible distances, the nonlinear dynamics of a fundamental soliton follows essentially the single-mode dynamics (short and middle range). However, for the higher-order solitons, the form of the evolution parameter suggests strong deviations of soliton dynamics from the single-mode with a square of soliton number. The use of enhanced-nonlinearity fibres and higher-order solitons might make the experimental studies of the specific quantum-soliton features more viable.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.optik.1optik.quatim

Time-frequency multiplexed single-photon source based on LiNbO3 modulators - Massaro, Marcello; Ansari, Vahid; Schlue, Fabian; Luo, Kai Hong; Herrmann, Harald; Brecht, Benjamin; Silberhorn, Christine; Dirmeier, Thomas; Marquardt, Christoph; Leuchs, Gerd (Optics InfoBase Conference Papers, 2020)
We present advances in the use of gigahertz LiNbO3 modulators enabling us programmable delays, which we will use to implement a multiplexed single-photon source, based on birefringent phase-matching in KTP waveguides.
CRIS-Team Scopus Importer:2020-11-13

Time-reversal symmetry in optics - Leuchs, Gerd; Sondermann, Markus (Physica Scripta, 2012)
The utilization of time-reversal symmetry in designing and implementing (quantum) optical experiments has become more and more frequent over the last few years. We review the basic idea underlying time-reversal methods, illustrate it with several examples and discuss a number of implications. © 2012 The Royal Swedish Academy of Sciences.

T-matrix analysis of dipole waves on chains of dielectric particles - Zhuromskyy, Oleksandr; Peschel, Ulf (7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, 2013)
Loss less propagation of longitudinal magnetic-dipole waves is predicted for regular chains of rutile particles. Rigorous T-matrix simulation techniques are applied to deduce the dispersion characteristics of the dipole waves and to optimize the properties of the closing elements in the waveguide for maximum power transmission. The proposed technique can be used to optimize the interaction between light and particle ensembles.
EAM Import::2019-03-13

Tomography and Correlation Function Measurements of Itinerant Microwave Photons - Eichler, Christopher; et al. (2011)
Keywords: wwwqudev

Tomography and Correlation Function Measurements of Itinerant Microwave Photons - Eichler, Christopher; et al. (Moriond 2011 - Quantum Mesoscopic Physics, 2011)
Keywords: wwwqudev

Tools for detecting entanglement between different degrees of freedom in quadrature squeezed cylindrically polarized modes - Gabriel, C.; Aiello, Andrea; Berg-Johansen, S.; Marquardt, Christoph; Leuchs, Gerd (European Physical Journal D, 2012)
Quadrature squeezed cylindrically polarized modes contain entanglement not only in the polarization and spatial electric field variables but also between these two degrees of freedom [C. Gabriel et al., Phys. Rev. Lett. 106, 060502 (2011)]. In this paper we present tools to generate and detect this entanglement. Experimentally we demonstrate the generation of quadrature squeezing in cylindrically polarized modes by mode transforming a squeezed Gaussian mode. Specifically, -1.2dB ± 0.1 dB of amplitude squeezing are achieved in the radially and azimuthally polarized mode. Furthermore, theoretically it is shown how the entanglement contained within these modes can be measured and how strong the quantum correlations are, depending on the measurement scheme. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.
CRIS-Team Scopus Importer:2022-06-05

Topology-dependent light transport in planar plasmonic-photonic architectures - Tuzakli, Refik; Vogel, Nicolas; Romanova, Alexandra; Romanov, Sergei G.; Peschel, Ulf (European Conference on Lasers and Electro-Optics, CLEO 2015, 2014)

Toward a Corrected Knife-Edge-Based Reconstruction of Tightly Focused Higher Order Beams - Orlov, Sergej; Huber, Christian; Marchenko, Pavel; Banzer, Peter; Leuchs, Gerd (Frontiers in Physics, 2020)
The knife-edge method is an established technique for profiling of even tightly focused light beams. However, the straightforward implementation of this method fails if the materials and geometry of the knife-edges are not chosen carefully or, in particular, if knife-edges are used that are made of pure materials. Artifacts are introduced in these cases in the shape and position of the reconstructed beam profile due to the interaction of the light beam under study with the knife. Hence, corrections to the standard knife-edge evaluation method are required. Here we investigate the knife-edge method for highly focused radially and azimuthally polarized beams and their linearly polarized constituents. We introduce relative shifts for those constituents and report on the consistency with the case of a linearly polarized fundamental Gaussian beam. An adapted knife-edge reconstruction technique is presented and proof-of-concept tests are shown, demonstrating the reconstruction of beam profiles.
CRIS-Team WoS Importer:2021-01-22

Toward High-Speed Nanoscopic Particle Tracking via Time-Resolved Detection of Directional Scattering - Beck, Paul; Neugebauer, Martin; Banzer, Peter (Laser & Photonics Reviews, 2020)
Owing to their immediate relevance for high precision position sensors, a variety of different sub-wavelength localization techniques has been developed in the past decades. However, many of these techniques suffer from low temporal resolution or require expensive detectors. Here, a method is presented that is based on the ultrafast detection of directionally scattered light with a quadrant photodetector operating at a large bandwidth, which exceeds the speed of most cameras. The directionality emerges due to the position dependent tailored excitation of a high-refractive index nanoparticle with a tightly focused vector beam. A spatial resolution of (Formula presented.) and a temporal resolution of (Formula presented.) is reached experimentally, which is not a fundamental but rather a technical limit. The detection scheme enables real-time particle tracking and sample stabilization in many optical setups sensitive to drifts and vibrations.
CRIS-Team Scopus Importer:2020-08-14
Keywords: directional scattering; tight focusing; ultrafast nanolocalization; vector beams

Towards Error-Corrected Quantum Computing with Superconducting Circuits - Eichler, Christopher (WE-Heraeus-Symposium: Recent Progress in Quantum Computing, 2022)
Keywords: wwwquantum

Towards fully integrated photonic displacement sensors - Bag, Ankan; Neugebauer, Martin; Mick, Uwe; Christiansen, Silke; Schulz, Sebastian A.; Banzer, Peter (Nature Communications, 2020)
The field of optical metrology with its high precision position, rotation and wavefront sensors represents the basis for lithography and high resolution microscopy. However, the on-chip integration—a task highly relevant for future nanotechnological devices—necessitates the reduction of the spatial footprint of sensing schemes by the deployment of novel concepts. A promising route towards this goal is predicated on the controllable directional emission of the fundamentally smallest emitters of light, i.e., dipoles, as an indicator. Here we realize an integrated displacement sensor based on the directional emission of Huygens dipoles excited in an individual dipolar antenna. The position of the antenna relative to the excitation field determines its directional coupling into a six-way crossing of photonic crystal waveguides. In our experimental study supported by theoretical calculations, we demonstrate the first prototype of an integrated displacement sensor with a standard deviation of the position accuracy below λ/300 at room temperature and ambient conditions.
CRIS-Team Scopus Importer:2020-06-16

Towards polarization-based excitation tailoring for extended Raman spectroscopy - Grosche, Simon; Hünermann, Richard; Sarau, George; Christiansen, Silke; Boyd, Robert W.; Leuchs, Gerd; Banzer, Peter (Optics Express, 2020)
Undoubtedly, Raman spectroscopy is one of the most elaborate spectroscopy tools in materials science, chemistry, medicine and optics. However, when it comes to the analysis of nanostructured specimens or individual sub-wavelength-sized systems, the access to Raman spectra resulting from different excitation schemes is usually very limited. For instance, the excitation with an electric field component oriented perpendicularly to the substrate plane is a difficult task. Conventionally, this can only be achieved by mechanically tilting the sample or by sophisticated sample preparation. Here, we propose a novel experimental method based on the utilization of polarization tailored light for Raman spectroscopy of individual nanostructures. As a proof of principle, we create three-dimensional electromagnetic field distributions at the nanoscale using tightly focused cylindrical vector beams impinging normally onto the specimen, hence keeping the traditional beam-path of commercial Raman systems. In order to demonstrate the convenience of this excitation scheme, we use a sub-wavelength diameter gallium-nitride nanostructure as a test platform and show experimentally that its Raman spectra depend sensitively on its location relative to the focal vector field. The observed Raman spectra can be attributed to the interaction with transverse and pure longitudinal electric field components. This novel technique may pave the way towards a characterization of Raman active nanosystems, granting direct access to growth-related parameters such as strain or defects in the material by using the full information of all Raman mode

Towards Quantum Noise Squeezing for 2-Micron Light with Tellurite and Chalcogenide Fibers with Large Kerr Nonlinearity - Sorokin, Arseny A.; Leuchs, Gerd; Corney, Joel F.; Kalinin, Nikolay A.; Anashkina, Elena A.; Andrianov, Alexey (Mathematics, 2022)
Squeezed light—nonclassical multiphoton states with fluctuations in one of the quadrature field components below the vacuum level—has found applications in quantum light spectroscopy, quantum telecommunications, quantum computing, precision quantum metrology, detecting gravitational waves, and biological measurements. At present, quantum noise squeezing with optical fiber systems operating in the range near 1.5 μm has been mastered relatively well, but there are no fiber sources of nonclassical squeezed light beyond this range. Silica fibers are not suitable for strong noise suppression for 2 µm continuous-wave (CW) light since their losses dramatically deteriorate the squeezed state of required lengths longer than 100 m. We propose the generation multiphoton states of 2-micron 10-W class CW light with squeezed quantum fluctuations stronger than −15 dB in chalcogenide and tellurite soft glass fibers with large Kerr nonlinearities. Using a realistic theoretical model, we numerically study squeezing for 2-micron light in step-index soft glass fibers by taking into account Kerr nonlinearity, distributed losses, and inelastic light scattering processes. Quantum noise squeezing stronger than −20 dB is numerically attained for a customized As2Se3 fibers with realistic parameters for the optimal fiber lengths shorter than 1 m. For commercial As2S3 and customized tellurite glass fibers, the expected squeezing in the −20–−15 dB range can be reached for fiber lengths of the order of 1 m.
CRIS-Team Scopus Importer:2022-10-28
Keywords: chalcogenide fibers; Kerr nonlinearity; quantum noise squeezing; stochastic nonlinear Schrödinger equation; tellurite fibers

Towards two-photon interference with a whispering gallery photon pair source - Schunk, Gerhard; Shafiee, Golnoush; Vogl, Ulrich; Strekalov, Dmitry; Otterpohl, Alexander; Sedlmeir, Florian; Schwefel, Harald G.L.; Leuchs, Gerd; Marquardt, Christoph (Optics InfoBase Conference Papers, 2016)
Down-converted photons from counterpropagating whispering gallery modes can be used to generate two-photon interference. We present our experimental scheme and discuss the interference visibility in case of backscattering.
CRIS-Team Scopus Importer:2022-06-05

Transverse Angular Momentum and Geometric Spin Hall Effect of Light - Aiello, Andrea; Lindlein, Norbert; Marquardt, Christoph; Leuchs, Gerd (Physical Review Letters, 2009)
We present a novel fundamental phenomenon occurring when a polarized beam of light is observed from a reference frame tilted with respect to the direction of propagation of the beam. This effect has a purely geometric nature and amounts to a polarization-dependent shift or split of the beam intensity distribution evaluated as the time-averaged flux of the Poynting vector across the plane of observation. We demonstrate that such a shift is unavoidable whenever the beam possesses a nonzero transverse angular momentum. This latter result has general validity and applies to arbitrary systems such as, e.g., electronic and atomic beams. © 2009 The American Physical Societ
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.transv

Transverse angular momentum of photons - Aiello, Andrea; Marquardt, Christoph; Leuchs, Gerd (Physical Review A - Atomic, Molecular, and Optical Physics, 2010)
We develop the quantum theory of transverse angular momentum of light beams. The theory applies to paraxial and quasiparaxial photon beams in vacuum and reproduces the known results for classical beams when applied to coherent states of the field. Both the Poynting vector, alias the linear momentum, and the angular-momentum quantum operators of a light beam are calculated including contributions from first-order transverse derivatives. This permits a correct description of the energy flow in the beam and the natural emergence of both the spin and the angular momentum of the photons. We show that for collimated beams of light, orbital angular-momentum operators do not satisfy the standard commutation rules. Finally, we discuss the application of our theory to some concrete cases. © 2010 The American Physical Society.
CRIS-Team Scopus Importer:2022-06-05

Transverse spinning of unpolarized light - Eismann, Jörg; Nicholls, L. H.; Roth, D. J.; Alonso, M. A.; Banzer, Peter; Rodriguez-Fortuno, F. J.; Zayats, A.; Nori, Franco; Bliokh, K. Y. (Nature Photonics, 2020)
It is well known that the spin angular momentum of light, and therefore that of photons, is directly related to their circular polarization. Naturally, for totally unpolarized light, polarization is undefined and the spin vanishes. However, for non-paraxial light, the recently discovered transverse spin component, orthogonal to the main propagation direction, is largely independent of the polarization state of the wave. Here, we demonstrate, both theoretically and experimentally, that this transverse spin survives even in non-paraxial fields (for example, focused or evanescent) generated from totally unpolarized paraxial light. This counterintuitive phenomenon is closely related to the fundamental difference between the meanings of 'full depolarization' for two-dimensional (2D) paraxial and 3D non-paraxial fields. Our results open an avenue for studies of spin-related phenomena and optical manipulation using unpolarized light.
CRIS-Team WoS Importer:2021-01-15

Trojan-horse attacks threaten the security of practical quantum cryptography - Jain, Nitin; Anisimova, Elena; Khan, Imran; Makarov, Vadim; Marquardt, Christoph; Leuchs, Gerd (New Journal of Physics, 2014)
A quantum key distribution (QKD) system may be probed by an eavesdropper Eve by sending in bright light from the quantum channel and analyzing the back-reflections. We propose and experimentally demonstrate a setup for mounting such a Trojan-horse attack. We show it in operation against the quantum cryptosystem Clavis2 from ID Quantique, as a proof-of-principle. With just a few back-reflected photons, Eve discerns Bob's (secret) basis choice, and thus the raw key bit in the Scarani-Acín-Ribordy-Gisin 2004 protocol, with higher than 90% probability. This would clearly breach the security of the cryptosystem. Unfortunately, Eve's bright pulses have a side effect of causing a high level of afterpulsing in Bob's single-photon detectors, resulting in a large quantum bit error rate that effectively protects this system from our attack. However, in a Clavis2-like system equipped with detectors with less-noisy but realistic characteristics, an attack strategy with positive leakage of the key would exist. We confirm this by a numerical simulation. Both the eavesdropping setup and strategy can be generalized to attack most of the current QKD systems, especially if they lack proper safeguards. We also propose countermeasures to prevent such attacks.
CRIS-Team Scopus Importer:2022-06-05
Keywords: quantum cryptography; quantum hacking; quantum key distribution; reflectometry; security proofs; Trojan horse

Truncated Metallo-Dielectric Omnidirectional Reflector: Collecting Single Photons in the Fundamental Gaussian Mode with 95% Efficiency - Li, Wancong; Morales Inostroza, Luis; Xu, Weiwang; Zhang, Pu; Renger, Jan; Götzinger, Stephan; Chen, Xue-Wen (ACS Photonics, 2020)
We propose a novel antenna structure that funnels single photons from a single emitter with unprecedented efficiency into a low-divergence fundamental Gaussian mode. Our device relies on the concept of creating an omnidirectional photonic bandgap to inhibit unwanted large-angle emission and to enhance small-angle defect-guided-mode emission. The new photon collection strategy is intuitively illustrated, rigorously verified, and optimized by implementing an efficient, body-of-revolution, finite-difference, time-domain method for in-plane dipole emitters. We investigate a few antenna designs to cover various boundary conditions posed by fabrication processes or material restrictions and theoretically demonstrate that collection efficiencies into the fundamental Gaussian mode exceeding 95% are achievable. Our antennas are broadband, insensitive to fabrication imperfections and compatible with a variety of solid-state emitters such as organic molecules, quantum dots, and defect centers in diamond. Unidirectional and low-divergence Gaussian-mode emission from a single emitter may enable the realization of a variety of photonic quantum computer architectures as well as highly efficient lightmatter interfaces.
CRIS-Team WoS Importer:2020-10-16

Tumbling and anomalous alignment of optically levitated anisotropic microparticles in chiral hollow-core photonic crystal fiber - Xie, Shangran; Sharma, Abhinav; Romodina, Maria; Joly, Nicolas; Russell, Philip St. John (Science Advances, 2021)
The complex tumbling motion of spinning nonspherical objects is a topic of enduring interest, both in popular culture and in advanced scientific research. Here, we report all-optical control of the spin, precession, and nutation of vaterite microparticles levitated by counterpropagating circularly polarized laser beams guided in chiral hollow-core fiber. The circularly polarized light causes the anisotropic particles to spin about the fiber axis, while, regulated by minimization of free energy, dipole forces tend to align the extraordinary optical axis of positive uniaxial particles into the plane of rotating electric field. The end result is that, accompanied by oscillatory nutation, the optical axis reaches a stable tilt angle with respect to the plane of the electric field. The results reveal new possibilities for manipulating optical alignment through rotational degrees of freedom, with applications in the control of micromotors and microgyroscopes, laser alignment of polyatomic molecules, and study of rotational cell mechanics.
CRIS-Team Scopus Importer:2021-07-30

Tuning the chirality of a dipole moment in an achiral particle with structured light - Eismann, Jörg; Neugebauer, Martin; Banzer, Peter (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
In the last decade, the attention drawn towards electric and magnetic dipole moments induced in optical nanoantennas significantly increased because of their numerous potential applications. For example, certain combinations of electric and magnetic dipoles allow for controlling the polarization state and propagation direction of light at the nanoscale [1,2]. The underlying effects rely on specific orientations and phase relations between the individual electric and magnetic dipole moments. In a recent work [3] we presented a new addition to the toolbox of experimental nanophotonics, the so-called σ-dipole, consisting of parallel electric and magnetic dipole moments phase shifted by ±π/2. The name originates from its well-defined near- and far-field helicity of ±1 [4]. Utilizing a combination of in-phase radially and azimuthally polarized beams, tightly focused onto a silicon nanoparticle, a well-defined and controllable superposition of both σ-dipoles can be realized.
CRIS-Team Scopus Importer:2019-11-15

Tuning the Optical and Geometrical Properties of Hybrid Carbon Flakes by Fabrication Parameters - Butt, Muhammad; Mamonova, Daria; Manshina, Alina A.; Banzer, Peter; Leuchs, Gerd (Optics InfoBase Conference Papers, 2020)
We investigate the effects of fabrication parameters on the properties of a selfassembled crystalline carbon-metal hybrid. We show that attenuation and geometrical parameters can be tuned, while high birefringence is observed for all studied cases.
CRIS-Team Scopus Importer:2020-11-13

Turning a molecule into a coherent two-level quantum system - Wang, Daqing; Kelkar, Hrishikesh; Martin-Cano, Diego; Rattenbacher, Dominik; Shkarin, Alexey; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Nature Physics, 2019)
The use of molecules in quantum optical applications has been hampered by incoherent internal vibrations and other phononic interactions with their environment. Here we show that an organic molecule placed into an optical microcavity behaves as a coherent two-level quantum system. This allows the observation of 99% extinction of a laser beam by a single molecule, saturation with less than 0.5 photons and non-classical generation of few-photons super-bunched light. Furthermore, we demonstrate efficient interaction of the molecule–microcavity system with single photons generated by a second molecule in a distant laboratory. Our achievements represent an important step towards linear and nonlinear quantum photonic circuits based on organic platforms.
CRIS-Team Scopus Importer:2019-05-17

Turning an organic molecule into a coherent two-level quantum system using a tunable fabry-perot microcavity - Wang, Daqing; Kelkar, Hrishikesh; Martin-Cano, Diego; Rattenbacher, Dominik; Shkarin, Alexey; Utikal, Tobias; Götzinger, Stephan; Sandoghdar, Vahid (Optics InfoBase Conference Papers, 2019)
By coupling an organic molecule to a Fabry-Perot microcavity, we turn it into a coherent two-level quantum system. We further demonstrate efficient interaction of this system with single photons generated by a second molecule.
CRIS-Team Scopus Importer:2019-07-09

Two-photon-absorption measurements in the presence of single-photon losses - Panahiyan, Shahram; Sanchez Munoz, Carlos; Chekhova, Maria; Schlawin, Frank (Physical Review A, 2022)
CRIS-Team WoS Importer:2022-11-04

Über die kluge Auswahl und Anwendung optischer 3D-Sensoren - Häusler, Gerd; et al. (Photonik, 2004)
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.optik.1optik.berdie

Ubiquitous coherence - boon and bale of the optical metrologist - Häusler, Gerd (Proceedings of SPIE, 2003)
Commonly, optical systems are called coherent, if a laser is used (right), and incoherent if other sources come into play (wrong). Most opticists are not aware that parasitic spatial coherence is ubiquitous, even if it is unobvious. The pretended incoherent approach may lead to significant quantitative measuring errors of illumination or reflectivity, 3d shape, size or distance. On the other hand, a favourable property of spatial coherence is that among the "speckle noise" we may reveal useful information about the object, by white light interferometry. This report will discuss simple rules to estimate the occuring errors and how to reduce spatial coherence. We will further discuss the complex signal formation in white light interferometry and roughness measurements far beyond the bandwidth limit of the observing optics.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.optik.1optik.ubiqui
Keywords: Coherence; Coherence radar; Measuring uncertainty; Roughness measurement; Speckle; Speckle noise; Superresolution; White light interferometry

Ultrafast spinning twisted ribbons of confined electric fields - Bauer, Thomas; Khonina, Svetlana N.; Golub, Ilya; Leuchs, Gerd; Banzer, Peter (Optica, 2020)
Topological properties of light attract tremendous attention in the optics communities and beyond. For instance, light beams gain robustness against certain deformations when carrying topological features, enabling intriguing applications. We report on the observation of a topological structure contained in an optical beam, i.e., a twisted ribbon formed by the electric field vector per se, in stark contrast to recently reported studies dealing with topological structures based on the distribution of the time averaged polarization ellipse. Moreover, our ribbons are spinning in time at a frequency given by the optical frequency divided by the total angular momentum of the incoming beam. The number of full twists of the ribbon is equal to the orbital angular momentum of the longitudinal component of the employed light beam upon tight focusing, which is a direct consequence of spin-to-orbit coupling. We study this angular-momentum-transfer-assisted generation of the twisted ribbon structures theoretically and experimentally for tightly focused circularly polarized beams of different vorticity, paving the way to tailored topologically robust excitations of novel coherent light-matter states.
CRIS-Team Scopus Importer:2020-10-23

Ultrahigh-Speed Imaging of Rotational Diffusion on a Lipid Bilayer - Mazaheri, Mahdi; Ehrig, Jens; Shkarin, Alexey; Zaburdaev, Vasily; Sandoghdar, Vahid (Nano Letters, 2020)
We studied the rotational and translational diffusion of a single gold nanorod linked to a supported lipid bilayer with ultrahigh temporal resolution of two microseconds. By using a home-built polarization-sensitive dark-field microscope, we recorded particle trajectories with lateral precision of 3 nm and rotational precision of 4°. The large number of trajectory points in our measurements allows us to characterize the statistics of rotational diffusion with unprecedented detail. Our data show apparent signatures of anomalous diffusion such as sublinear scaling of the mean-squared angular displacement and negative values of angular correlation function at small lag times. However, a careful analysis reveals that these effects stem from the residual noise contributions and confirms normal diffusion. Our experimental approach and observations can be extended to investigate diffusive processes of anisotropic nanoparticles in other fundamental systems such as cellular membranes or other two-dimensional fluids.
CRIS-Team Scopus Importer:2020-10-30
Keywords: anomalous diffusion; dark-field microscopy; nanorod; rotational diffusion; scattering; single particle tracking

Ultra-Low Concentration Monitoring of Catalytic Reactions in Photonic Crystal Fiber - Cubillas, Ana Maria; Schmidt, Matthias; Scharrer, Michael; Euser, Tijmen G.; Etzold, Bastian; Taccardi, Nicola; Wasserscheid, Peter; Russell, Philip St. John (Chemistry - A European Journal, 2012)
Photonic crystal fibers as microreactors: Photonic crystal fibers can be used as microreactors (see figure). As an example, the illustration shows the difference in size between a 10cm cuvette (left), and a photonic crystal fiber (right; not to scale).

Ultra-narrow linewidth CW sub-THz generation using GS based OFCG and n-i-pn-i-p superlattice photomixers - Criado, Ruben; de Dios, Christina; Döhler, Gottfried; Preu, Sascha; Malzer, Stefan; Bauerschmidt, Sebastian; Lu, Hong; Gossard, Art; Acedo, Pablo (Electronics Letters, 2012)
A report is presented on the photonic synthesis of ultra-narrow linewidth continuous-wave (CW) sub-THz signals using a gain-switching (GS) based optical frequency comb generator (OFCG), selective optical filtering and a n-i-pn-i-p superlattice photomixer. This setup provides continuous tunability with a tuning resolution in the range of 0.1Hz at 120GHz and full width at half maximum of the generated signals below the limits of the measurement setup (<10Hz). The advantages of this system make it a very good candidate for applications requiring extremely low phase noise and continuous tunability, such as high resolution spectroscopy in the sub-THz and THz range. © 2012 The Institution of Engineering and Technology.

Ultra-short laser surface properties optimization of biocompatibility characteristics of 3d poly-ε-caprolactone and hydroxyapatite composite scaffolds - Daskalova, Albena; Filipov, Emil; Angelova, Liliya; Stefanov, Radostin; Tatchev, Dragomir; Avdeev, Georgi; Sotelo, Lamborghini; Christiansen, Silke; Sarau, George; Leuchs, Gerd; Iordanova, Ekaterina; Buchvarov, Ivan (Materials, 2021)
The use of laser processing for the creation of diverse morphological patterns onto the surface of polymer scaffolds represents a method for overcoming bacterial biofilm formation and inducing enhanced cellular dynamics. We have investigated the influence of ultra-short laser pa-rameters on 3D-printed poly-ε-caprolactone (PCL) and poly-ε-caprolactone/hydroxyapatite (PCL/HA) scaffolds with the aim of creating submicron geometrical features to improve the matrix biocompatibility properties. Specifically, the present research was focused on monitoring the effect of the laser fluence (F) and the number of applied pulses (N) on the morphological, chemical and mechanical properties of the scaffolds. SEM analysis revealed that the femtosecond laser treatment of the scaffolds led to the formation of two distinct surface geometrical patterns, microchannels and single microprotrusions, without triggering collateral damage to the surrounding zones. We found that the microchannel structures favor the hydrophilicity properties. As demonstrated by the com-puter tomography results, surface roughness of the modified zones increases compared to the non-modified surface, without influencing the mechanical stability of the 3D matrices. The X-ray diffraction analysis confirmed that the laser structuring of the matrices did not lead to a change in the semi-crystalline phase of the PCL. The combinations of two types of geometrical designs—wood pile and snowflake—with laser-induced morphologies in the form of channels and columns are considered for optimizing the conditions for establishing an ideal scaffold, namely, precise dimensional form, mechanical stability, improved cytocompatibility and antibacterial behavior.
CRIS-Team Scopus Importer:2021-12-31
Keywords: Antibacterial structuring; Biodegradable polymers; Bone tissue engineering; Surface patterns; Ultra-short laser processing

Unbiased retrieval of frequency-dependent mechanical properties from noisy time-dependent signals - Abuhattum, Shada; Kuan, Hui Shun; Müller, Paul; Guck, Jochen; Zaburdaev, Vasily (Biophysical Reports, 2022)
The mechanical response of materials to dynamic loading is often quantified by the frequency-dependent complex modulus. Probing materials directly in the frequency domain faces technical challenges such as a limited range of frequencies, long measurement times, or small sample sizes. Furthermore, many biological samples, such as cells or tissues, can change their properties upon repetitive probing at different frequencies. Therefore, it is common practice to extract the material properties by fitting predefined mechanical models to measurements performed in the time domain. This practice, however, precludes the probing of unique and yet unexplored material properties. In this report, we demonstrate that the frequency-dependent complex modulus can be robustly retrieved in a model-independent manner directly from time-dependent stress-strain measurements. While applying a rolling average eliminates random noise and leads to a reliable complex modulus in the lower frequency range, a Fourier transform with a complex frequency helps to recover the material properties at high frequencies. Finally, by properly designing the probing procedure, the recovery of reliable mechanical properties can be extended to an even wider frequency range. Our approach can be used with many state-of-the-art experimental methods to interrogate the mechanical properties of biological and other complex materials.
CRIS-Team Scopus Importer:2022-08-05

Unconditional quantum cloning of coherent states with linear optics - Leuchs, Gerd; et al. (Physical Review Letters, 2005)
A scheme for optimal Gaussian cloning of optical coherent states is proposed and experimentally demonstrated. Its optical realization is based entirely on simple linear optical elements and homodyne detection. The optimality of the presented scheme is limited only by detection inefficiencies. Experimentally, we achieved a cloning fidelity of about 65%, which almost touches the optimal value of 2/3. © 2005 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.optik.1optik.uncond

Understanding GaN/InGaN core-shell growth towards high quality factor whispering gallery modes from non-polar InGaN quantum wells on GaN rods. - Tessarek, Christian; Rechberger, Stefanie; Dieker, Christel; Heilmann, Martin; Spiecker, Erdmann; Christiansen, S. H. (Nanotechnology, 2017)
GaN microrods are used as a basis for subsequent InGaN quantum well (QW) and quantum dot deposition by metal-organic vapor phase epitaxy. The coverage of the shell along the sidewall of rods is dependent on the rod growth time and a complete coverage is obtained for shorter rod growth times. Transmission electron microscopy measurements are performed to reveal the structural properties of the InGaN layer on the sidewall facet and on the top facet. The presence of layers in the microrod and on the microrod surface will be discussed with respect to GaN and InGaN growth. A detailed model will be presented explaining the formation of multiple SiN layers and the partial and full coverage of the shell around the core. Cathodoluminescence measurements are performed to analyze the InGaN emission properties along the microrod and to study the microresonator properties of such hexagonal core-shell structures. High quality factor whispering gallery modes with [Formula: see text] are reported for the first time in a GaN microrod/InGaN non-polar QW core-shell geometry. The GaN/InGaN core-shell microrods are expected to be promising building blocks for low-threshold laser diodes and ultra-sensitive optical sensors.
Keywords: GaN; InGaN; SiN; rods; core–shell; quantum wells; whispering gallery modes

"Und er würfelt doch!" - Optische Experimente zum Quantenzufall - Bronner, Patrick; Strunz, Andreas; Silberhorn, Christine; Meyn, Jan-Peter (Praxis der Naturwissenschaften - Physik in der Schule, 2013)
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.PI.PDP.underw

Unfolding the Hong-Ou-Mandel interference between heralded photons from narrowband twin beams - Laiho, Kaisa; Dirmeier, Thomas; Shafiee, Golnoush; Marquardt, Christoph (New Journal of Physics, 2023)
The Hong-Ou-Mandel (HOM) interference is one of the most intriguing quantum optical phenomena and crucial in performing quantum optical communication and computation tasks. Lately, twin beam emitters such as those relying on the process of parametric down-conversion (PDC) have become confident sources of heralded single photons. However, if the pump power is high enough, the pairs produced via PDC—often called signal and idler—incorporate multiphoton contributions that usually distort the investigated quantum features. Here, we derive the temporal characteristics of the HOM interference between heralded states from two independent narrowband PDC sources. Apart from the PDC multiphoton content, our treatment also takes into account effects arriving from an unbalanced beam splitter ratio and optical losses. We perform a simulation in the telecommunication wavelength range and provide a useful tool for finding the optimal choice for PDC process parameters. Our results offer insight in the properties of narrowband PDC sources and turn useful when driving quantum optical applications with them.<br

Universal optical amplification without nonlinearity - Leuchs, Gerd; et al. (Physical Review Letters, 2006)
We propose and realize a novel universal phase insensitive optical amplifier operating at the quantum limit in the low gain regime. The amplifier consists only of linear optics and detectors thus circumventing a nonlinear interaction. © 2006 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.univer

Universelles wellenoptisches Phasenprüfgerät - Lindlein, Norbert; et al. (FORMIKROSYS-Sonderteil von F&M, 2001)
UnivIS-Import:2015-04-20:Pub.2001.nat.dphy.optik.1optik.univer

Untersuchung der Abweichungen zwischen skalarer und rigoroser Rechnung an CGHs in Twyman-Green-Interferometern zur Linsenprüfung - Iff, Wolfgang; Glaubrecht, Stefan; Lindlein, Norbert; Schwider, Johannes (DGaO Proceedings 2010 – http://www.dgao-proceedings.de – ISSN: 1614-8436, 2010)

Untersuchungen zum Stofftransport ausgewählter Substanzen in überkritischem Kohlendioxid mittels Shearing-Intereferometrie - Hu, Miao; Benning, Rainer; Ertunc, Özgür; Bielke, Thorsten; Delgado, Antonio; Neukam, Johannes; Nercissian, Vanusch; Berger, Andreas (Proceedings der 19. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 2011)
UnivIS-Import:2015-04-16:Pub.2011.tech.ITC.stmmec.unters

Untersuchung von Phasensingularitäten in der Umgebung kleiner Strukturen mit einem Linnik-Interferenzmikroskop - Leuchs, Gerd; et al. (Technisches Messen, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.optik.1optik.unters

Untreated ´blow-in´ fracture of the orbital floor causing a mucocele: report of an unusual late complication - Nkenke, Emeka; Häusler, Gerd; et al. (Journal of Cranio-Maxillofacial Surgery, 2005)
Background: Several severe complications have been described with blow-in fractures. Therefore, immediate surgical treatment of these fractures has been recommended. To date, there is only minimal knowledge on long-term complications of blow-in fractures that have remained untreated. The present case report describes a late complication of an untreated blow-in fracture of the orbital floor. Case: A 37-year-old male was involved in a car accident 16 years before. At that time, a non-dislocated midfacial fracture was diagnosed and remained untreated because of the lack of clinical symptoms. Four months before surgery an exophthalmos of the left globe began to develop. CT examination revealed a consolidated blow-in fracture of the left orbital floor and an opaque mass around the dislocated bony fragments. By an infraorbital approach the bony fragments and the surrounding mass were removed. Histological examination of the removed material revealed a cystic structure lined with respiratory epithelium. Therefore, the diagnosis 'post-traumatic mucocele in the orbit caused by dislocated respiratory epithelium from the maxillary sinus' was made. Conclusion: Even if blow-in fractures do not cause complications immediately after trauma, late complications like mucoceles can occur after several symptom-free years. Therefore, early reconstruction should be intended even in asymptomatic cases of blow-in fractures with minimal displacement of the bony fragments. © 2005 European Association for Cranio-Maxillofacial Surgery.
UnivIS-Import:2015-04-14:Pub.2005.nat.dphy.optik.1optik.untrea
Keywords: Alloplastic reconstruction of the orbital floor; Blow-in fracture; Exophthalmos; Mucocele; Untreated orbital floor fracture

Use of Fiber Nonlinearities for Signal Improvement in Optical Transmission Systems - Schmauß, Bernhard; Holtmannspötter, Michael; Stephan, Christian; Sponsel, Klaus; Onishchukov, Georgy; Leuchs, Gerd (Frequenz, 2009)
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.optik.1optik.useoff

Using a quantum well heterostructure to study the longitudinal and transverse electric field components of a strongly focused laser beam - Malzer, Stefan; Leuchs, Gerd; et al. (Journal of Applied Physics, 2006)
We report a method to measure the electric energy density of longitudinal and transverse electric field components of strongly focused polarized laser beams. We used a quantum well photodetector and exploited the polarization dependent optical transitions of light holes and heavy holes to probe the electric field distribution in the focal region. A comparison of the measured photocurrent spectra for radially and azimuthally polarized beams at the light and heavy hole absorption peaks provides a measure of the amount of the longitudinal electric field component. © 2006 American Institute of Physics.

Using saturation effects in a nonlinear amplifying loop mirror for multilevel phase-preserving amplitude regeneration - Roethlingshoefer, Tobias; Onishchukov, Georgy; Schmauß, Bernhard; Leuchs, Gerd (Transparent Optical Networks (ICTON), 2011 13th International Conference on, 2011)
The influence of amplifier gain saturation in nonlinear amplifying loop mirror on simultaneous phase-preserving regeneration of two power states has been studied. Numeri cal simulations have shown an improvement of up to 4 dB for the first, low-power state and 8 dB for the se cond high-power state. Compar ed to the linear amplifier case an improvement of 3 dB for the se cond power state has been achieved.
lhft_intern.bib::Roethlingshoefer2011a
Keywords: 2R regeneration; quadrature amplitude modulation; NALM; NOLM

Using Supercritical Carbon Dioxide for Physical Foaming of Advanced Polymer Materials - Wolff, Friederich; Zirkel, Larissa; Sarah, Betzold; Jakob, Matthias; Verena, Maier; Nachtrab, Frank; Ceron Nicolat, Bruno; Fey, Tobias; Münstädt, Helmut (International Polymer Processing, 2011)
Foams from high performance polymers find more and more interest. The processes to generate them can be difficult, however. It is shown how physical foaming with CO2 can be used as a first step to assess the potentials of such materials. For investigations of such kind an autoclave on a laboratory scale which allows pressure variations up to 300 bars and temperatures up to 300 degrees C was set up. The samples are saturated with supercritical carbon dioxide (s.c. CO2) which acts as a foaming agent. Depending on the process and material parameters different foam characteristics and cell morphologies were obtained and characterised. The potential of this method is demonstrated for two different classes of advanced polymer materials, thermoplastic fluoropolymers (PEP), and a silicone resin. In the case of the fluoropolymer, previously prepared films were foamed and the effects of various process parameters on the foam characteristics were investigated. Besides the general potential of foams from fluoropolymers, they are candidates for polymeric piezoelectric materials with a relatively high temperature stability. Silicone polymers possess some properties superior to common organic polymers. First results on the foaming behaviour of a silicone resin are presented.

Vector helical bloch modes in N-fold rotationally symmetric waveguiding structures: Spin and Azimuthal order - Russell, Philip St. John; Chen, Yang; Roth, Paul; Wong, Gordon K. L. (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Many different techniques have been used to model the electromagnetic response of photonic crystal fibres (PCFs) and waveguide arrays. Here we introduce a new vectorial approach based on helical Bloch waves (hBWs) that appear in structures (such as many PCFs) that are N-fold rotationally symmetric (symmetry group Cn), i.e., they repeat perfectly in N sectors over 2π, when viewed in a cylindrical coordinate frame [1]. Helical Bloch waves can also carry optical angular momentum: a complex Bloch wave field propagates azimuthally around the axis of the structure, forming helical Bloch modes (hBMs) when a certain azimuthal resonance condition is satisfied.
CRIS-Team Scopus Importer:2019-11-15

Vectorial vortex generation and phase singularities upon Brewster reflection - Barczyk, Rend; Nechayev, Sergey; Butt, Muhammad Abdullah; Leuchs, Gerd; Banzer, Peter (Physical Review A, 2019)
We experimentally demonstrate the emergence of an azimuthally polarized vectorial vortex beam with a phase singularity upon Brewster reflection of focused circularly polarized light from a dielectric substrate. The effect originates from the polarizing properties of the Fresnel reflection coefficients described in Brewster's law. An astonishing consequence of this effect is that the reflected field's Cartesian components acquire local phase singularities at Brewster's angle. Our observations are crucial for polarization microscopy and open avenues for the generation of exotic states of light based on spin-to-orbit coupling, without the need for sophisticated optical elements.
CRIS-Team WoS Importer:2019-07-02
Keywords: Angular momentum of light; Classical optics; Geometrical & wave optics; Imaging & optical processing; Light propagation; transmission & absorption; Optical vortices; Optics & lasers; Polarization of light

Verifying continuous variable entanglement of intense light pulses - Leuchs, Gerd; et al. (Physical Review A, 2006)
Three different methods have been discussed to verify continuous variable entanglement of intense light beams. We demonstrate all three methods using the same setup to facilitate the comparison. The nonlinearity used to generate entanglement is the Kerr effect in optical fibers. Due to the brightness of the entangled pulses, standard homodyne detection is not an appropriate tool for the verification. However, we show that by using large asymmetric interferometers on each beam individually, two noncommuting variables can be accessed and the presence of entanglement verified via joint measurements on the two beams. Alternatively, we witness entanglement by combining the two beams on a beam splitter that yields certain linear combinations of quadrature amplitudes which suffice to prove the presence of entanglement. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.optik.1optik.verify

Vermessung konvexer, rauer Asphären mittels Interferometrie in streifender Inzidenz - Rothau, Sergej; Schwider, Johannes; Mantel, Klaus; Lindlein, Norbert (120. Annual Meeting of the DGaO, 2019)

Versatile source of polarization-entangled photons - Maser, Andreas; Wiegner, Ralph; Schilling, Uwe; Thiel, Christoph; von Zanthier, Joachim (Physical Review A, 2010)
We propose a method for the generation of a large variety of entangled states, encoded in the polarization degrees of freedom of N photons, within the same experimental setup. Starting with uncorrelated photons, emitted from N arbitrary single-photon sources, and using linear optical tools only, we demonstrate the creation of all symmetric states (e. g., GHZ and W states), as well as all symmetric and nonsymmetric total angular momentum eigenstates of the N-qubit compoun

Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer - Heilmann, Martin; Munshi, A. Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T.; van Helvoort, Antonius T. J.; Yang, Jianfeng; Latzel, Michael; Hoffmann, Bjoern; Conibeer, Gavin; Weman, Helge; et al. (Nano Letters, 2016)
The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.
Keywords: GaN; GaN-on-Si; graphene; MOVPE; nanorods

Viscoelastic properties of suspended cells measured with shear flow deformation cytometry - Gerum, Richard; Mirzahossein, Elham; Eroles, Mar; Elsterer, Jennifer; Mainka, Astrid; Bauer, Andreas; Sonntag, Selina; Winterl, Alexander; Bartl, Johannes; Fischer, Lena; Abuhattum, Shada; Goswami, Ruchi; et al. (eLife, 2022)
Numerous cell functions are accompanied by phenotypic changes in viscoelastic prop-erties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microflu-idic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.
CRIS-Team Scopus Importer:2022-10-28

Visualization and Detection of Small Defects on Car-Bodies - Häusler, Gerd; et al. (Proc. of Vision, Modeling and Visualization '99, 1999)
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.optik.1optik.visual

Visualization and ligand-induced modulation of dopamine receptor dimerization at the single molecule level - Tabor, Alina; Weisenburger, S; Banerjee, Ashutosh; Purkayastha, Nirupam; Kaindl, Jonas; Hübner, Harald; Wei, Luxi; Groemer, Teja W.; Kornhuber, Johannes; Tschammer, Nuska; Birdsall, Nigel J.M.; Mashanov, Gregory I.; et al. (Scientific Reports, 2016)
G protein-coupled receptors (GPCRs), including dopamine receptors, represent a group of important pharmacological targets. An increased formation of dopamine receptor D-2 homodimers has been suggested to be associated with the pathophysiology of schizophrenia. Selective labeling and ligand-induced modulation of dimerization may therefore allow the investigation of the pathophysiological role of these dimers. Using TIRF microscopy at the single molecule level, transient formation of homodimers of dopamine receptors in the membrane of stably transfected CHO cells has been observed. The equilibrium between dimers and monomers was modulated by the binding of ligands; whereas antagonists showed a ratio that was identical to that of unliganded receptors, agonist-bound D-2 receptor-ligand complexes resulted in an increase in dimerization. Addition of bivalent D-2 receptor ligands also resulted in a large increase in D2 receptor dimers. A physical interaction between the protomers was confirmed using high resolution cryogenic localization microscopy, with ca. 9 nm between the centers of mass.

Visualizing cellular secretion with single-protein sensitivity via interferometric scattering microscopy (iSCAT) - Gemeinhardt, André; König, Katharina; Nicoli, Francesca; Dahmardeh, Mahyar; Sandoghdar, Vahid (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Proteins are involved in a large number of biological processes. Apart from the field of proteomics, where ensemble studies of the entire set of proteins present in a system are carried out, detection and analysis of single proteins has become a vibrant field of research. Particularly, the study of proteins that are secreted from cells into the extracellular space is an important topic with wide implications for basic intercellular interactions and immunology. Secretory proteins are responsible for a vast amount of cellular functions involving migration, wound healing, immunological response, or intercellular communication. Challenges in the traditional methods such as immunoassays, Western blotting, mass spectrometry, or fluorescence microscopy are the need for labeling (with immunological complements, isotopes, or fluorescent markers) and the necessary processing and separation steps that hinder high temporal resolution in dynamic studies. Today, none of the existing techniques is able to detect single proteins secreted from living cells at subsecond temporal resolution without the need for labeling.
CRIS-Team Scopus Importer:2019-11-15

Visualizing Single-Cell Secretion Dynamics with Single-Protein Sensitivity - McDonald, Matthew; Gemeinhardt, André; König, Katharina; Piliarik, Marek; Schaffer, Stefanie; Völkl, Simon; Aigner, Michael; Mackensen, Andreas; Sandoghdar, Vahid (Nano Letters, 2017)
Cellular secretion of proteins into the extracellular environment is an essential mediator of critical biological mechanisms, including cell-to-cell communication, immunological response, targeted delivery, and differentiation. Here, we report a novel methodology that allows for the real-time detection and imaging of single unlabeled proteins that are secreted from individual living cells. This is accomplished via interferometric detection of scattered light (iSCAT) and is demonstrated with Laz388 cells, an Epstein-Barr virus (EBV)-transformed B cell line. We find that single Laz388 cells actively secrete IgG antibodies at a rate of the order of 100 molecules per second. Intriguingly, we also find that other proteins and particles spanning ca. 100 kDa-1 MDa are secreted from the Laz388 cells in tandem with IgG antibody release, likely arising from EBV-related viral proteins. The technique is general and, as we show, can also be applied to studying the lysate of a single cell. Our results establish label-free iSCAT imaging as a powerful tool for studying the real-time exchange between cells and their immediate environment with single-protein sensitivity.
EVALuna2:25781

Wave aberration measurement using microlens arrays - Lindlein, Norbert; et al. (EOS Topical Meetings DigestSeries, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.optik.1optik.waveab

Wave-front reconstruction with a Shack-Hartmann sensor with an iterative spline fitting method - Lindlein, Norbert; et al. (Applied Optics, 2000)
One limitation of the conventional Shack-Hartmann sensor is that the spots of each microlens have to remain in their respective subapertures. We present an algorithm that assigns the spots to their reference points unequivocally even if they are situated far outside their subaperture. For this assignment a spline function is extrapolated in successive steps of the iterative algorithm. The proposed method works in a single-shot technique and does not need any aid from mechanical devices. The reconstruction of a simulated steep aspherical wave front (∼100lλ/mm slope) is described as well as experimental results of the measurement of a spherical wave front with a huge peak-to-valley value (∼400l). The performance of the method is compared with the unwrapping method, which has been published before. © 2000 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.optik.1optik.wavefr

Waveguide properties of single subwavelength holes demonstrated with radially and azimuthally polarized light - Banzer, Peter; Leuchs, Gerd; et al. (Applied Physics B-Lasers and Optics, 2007)
We investigate the transmission of focused beams through single subwavelength holes in a silver film. We use radially and azimuthally polarized light to excite higher-order waveguide modes as well as to match the radial symmetry of the aperture geometry. Remarkably, the transmission properties can be described by a classical waveguide model even for thicknesses of the silver film as thin as a quarter of a wavelength. © 2007 Springer-Verlag.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.optik.1optik.wavegu

Wavelength mismatch correcting elements for volume holograms written on a laser pattern generator - Lindlein, Norbert; et al. (Journal of Modern Optics, 1993)
Holographic optical lenses based on volume gratings commonly suffer from severe aberrations due to wavelength mismatch between recording (blue-sensitive material) and application (often employing diode lasers). Here, methods are described for the precompensation of the aberrations at the recording. Both, aberrations in the phase of the reconstructed wave from the desired wave ('wave aberration'), as well as aberrations in intensity resulting from deviations from the Bragg condition during reconstruction ('Bragg aberration') need to be compensated for. The design method for generating the computer generated holograms is described which are used as precompensating elements in the recording step of the interferometrically produced holographic optical elements. The computer generated holograms are written on a laser pattern generator. Test results of our laser pattern generator are shown to demonstrate its capability for this process. The measurement of the aberrations at the design wavelength in the near infrared is a very important step because it allows to eliminate in a second recording process misadjustment errors which will occur during the first recording step. By modification of at least one of the computer generated holograms the convergence of the procedure can be achieved. © 1993 Taylor & Francis Ltd.

Wave-optical simulation of a grating lateral shearing interferometer with a periodic incoherent light source - Lindlein, Norbert; et al. (Photon Management III, 2008)
A quite simple numerical model for the wave-optical simulation of the interference in a grating lateral shearing interferometer with a periodic light source and a large lateral shear is presented. Aberrations of the collimating lens will generate a spatially varying modulation in the interference pattern. The model assumes that the light source itself is completely spatially incoherent so that only the light from each point of the light source has to be propagated wave-optically through the optical system. Then, the intensity distributions of all light source points in the detector plane can just be added. The simulations are compared to theoretical calculations of partial coherence theory and also to experimental results.
Keywords: Coherence; Grating lateral shearing interferometer; Partial coherence; Periodic light source; Shearing interferometer; Wave-optical simulation

Wave Optics - Lindlein, Norbert; Leuchs, Gerd (Handbook of Lasers and Optics, 2007)
UnivIS-Import:2015-04-20:Pub.2007.nat.dphy.optik.1optik.waveop

Wave phenomena and wave equations - Leuchs, Gerd (Proceedings of the International School of Physics "Enrico Fermi", 2019)
For any kind of wave phenomenon one can find ways to derive the respective dispersion relation from experimental observations and measurements. This dispersion relation determines the structure of the wave equation and thus characterizes the dynamics of the respective wave. Different wave phenomena are thus governed by different differential equations. Here we want to emphasize the experimental approach to matter waves, but before doing so we will discuss and test the procedure for other types of waves, in particular water waves.
CRIS-Team Scopus Importer:2019-06-21

Weak Measurement Enhanced Spin Hall Effect of Light for Particle Displacement Sensing - Neugebauer, Martin; Nechayev, Sergey; Vorndran, Martin; Leuchs, Gerd; Banzer, Peter (Nano Letters, 2019)
A spherical nanoparticle can scatter tightly focused optical beams in a spin-segmented manner, meaning that the far field of the scattered light exhibits laterally separated left- and right-handed circularly polarized components. This effect, commonly referred to as giant spin Hall effect of light, strongly depends on the position of the scatterer in the focal volume. Here, a scheme that utilizes an optical weak measurement in a cylindrical polarization basis is put forward to drastically enhance the spin-segmentation and, therefore, the sensitivity to small displacements of a scatterer. In particular, we experimentally achieve a change of the spin-splitting signal of 5% per nanometer displacement.
CRIS-Team Scopus Importer:2019-05-07
Keywords: localization; scattering; spin Hall effect; structured light; Weak measurement

Wellenfrontsensor für den Optical Workshop - Lindlein, Norbert; et al. (Laser, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.optik.1optik.wellen

Whispering gallery mode optical parametric oscillators - Marquardt, Christoph (Optics InfoBase Conference Papers, 2013)
Crystalline whispering gallery resonators with strong second order nonlinearities offer highly efficient and tuneable nonlinear processes in a very compact and stable setup. I will give an introduction and review recent developments. © OSA 2013.
CRIS-Team Scopus Importer:2022-06-05

White-light interferometer with dispersion - an accurate fiber-optic sensor for the measurement of distance - Häusler, Gerd; et al. (Applied Optics, 2005)
We present a fiber-optical sensor for distance measurement of smooth and rough surfaces that is based on white-light interferometry; the sensor measures the distance from the sample surface to the sensor head. Because white light is used, the measurement is absolute. The measurement uncertainty depends not on the aperture of the optical system but only on the properties of the rough surface and is commonly ∼ 1 μm. The measurement range is approximately 1 mm. The sensor includes no mechanical moving parts; mechanical movement is replaced by the spectral decomposition of light at the interferometer output. The absence of mechanical moving parts enables a high measuring rate to be reached. © 2005 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.optik.1optik.whitel