% Encoding: UTF-8 @COMMENT{BibTeX export based on data in FAU CRIS: https://cris.fau.de/} @COMMENT{For any questions please write to cris-support@fau.de} @article{faucris.220877215, abstract = {Existing for almost four decades, liquid crystal on Silicon (LCOS) technology is rapidly growing into photonic applications. We review the basics of the technology, front the wafer to the driving solutions, the progress over the last decade and the future outlook. Furthermore we review the most exciting industrial and scientific applications of the LCOS technology. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, author = {Lazarev, Grigory and Chen, Po-Ju and Strauß, Johannes and Fontaine, Nicolas and Forbes, Andrew}, doi = {10.1364/OE.27.016206}, faupublication = {yes}, journal = {Optics Express}, note = {CRIS-Team WoS Importer:2019-06-18}, pages = {16206-16249}, peerreviewed = {Yes}, title = {{Beyond} the display: phase-only liquid crystal on {Silicon} devices and their applications in photonics [{Invited}]}, volume = {27}, year = {2019} } @inproceedings{faucris.121596904, abstract = {Electro-optical deflectors (EOD) and acousto-optical deflectors (AOD) are based on deflection of laser light within a solid state medium. As they do not contain any moving parts, they yield advantages compared to mechanical scanners which are conventionally used for laser beam deflection. Even for arbitrary scan paths high feed rates can be achieved. In this work the principles of operation and characteristic properties of EOD and AOD are presented. Additionally, a comparison to mirror based mechanical deflectors regarding deflection angles, speed and accuracy is made in terms of resolvable spots and the rate of resolvable spots. Especially, the latter one is up to one order of magnitude higher for EOD and AOD systems compared to conventional systems. Further characteristic properties such as response time, damage threshold, efficiency and beam distortions are discussed. Solid state laser beam deflectors are usually characterized by small deflection angles but high angular deflection velocities. As mechanical deflectors exhibit opposite properties an arrangement of a mechanical scanner combined with a solid state deflector provides a solution with the benefits of both systems. As ultrashort pulsed lasers with average power above 100 W and repetition rates in the MHz range have been available for several years this approach can be applied to fully exploit their capabilities. Thereby, pulse overlap can be reduced and by this means heat affected zones are prevented to provide proper processing results. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.}, address = {Bellingham, WA}, author = {Heberle, Johannes and Bechtold, Peter and Strauß, Johannes and Schmidt, Michael}, booktitle = {Laser-based Micro- and Nanoprocessing X, Proc. SPIE 9736}, date = {2016-02-13/2016-02-18}, doi = {10.1117/12.2212208}, editor = {Klotzbach, Udo; Washio, Kunihiko; Arnold, Craig B.}, faupublication = {yes}, isbn = {9781628419719}, keywords = {laser beam scanner; electro-optical deflector; acousto-optical deflector;}, pages = {97360L-1 - 97360L-10}, peerreviewed = {No}, publisher = {SPIE}, title = {{Electro}-optic and acousto-optic laser beam scanners}, venue = {San Francisco}, year = {2016} } @article{faucris.123676784, abstract = {Tailored intensity distribution enables efficient microstructuring as the maximum pulse energy of an ultrashort-pulsed laser can be applied. Dynamic adaptation of the intensity profile can be realized by holographic laser beam shaping using phase-only liquid crystal on silicon (LCoS) displays as a spatial light modulator (SLM). To achieve the desired intensity profile at the focal plane an accurate phase retardation of the SLM's liquid crystals has to be guaranteed. In this publication we present the phase calibration of three LCoS SLM from different manufacturers. Each system is evaluated for direct laser structuring applications. As one of the tested SLM show a spatially nonlinear behavior, a compensation method proposed by Engström et al. in 2013 is applied. Finally, the necessity of this phase calibration is presented and discussed by applying a squared flat-top profile.}, author = {Strauß, Johannes and Häfner, Tom and Dobler, Michael and Heberle, Johannes and Schmidt, Michael}, doi = {10.1016/j.phpro.2016.08.122}, faupublication = {yes}, journal = {Physics Procedia}, keywords = {laser; diffractive optics; holographic beam shaping; spatial light modulator}, pages = {1160-1169}, peerreviewed = {Yes}, title = {{Evaluation} and {Calibration} of {LCoS} {SLM} for {Direct} {Laser} {Structuring} with {Tailored} {Intensity} {Distributions}}, url = {http://www.sciencedirect.com/science/article/pii/S1875389216302292}, volume = {83}, year = {2016} } @article{faucris.108609864, abstract = {Fabrication of phase only holograms via spatially selective ablation of an ITO nanoparticulate layer coated on an optical quality transparent substrate appears to be very attractive due to the simplicity and flexibility of this approach. A pre-calculated binary pattern can be directly written on such a layer in order to produce a desired intensity distribution in the focal plane of a focusing lens. In this contribution we analyze the performance of the fabricated holograms and their suitability for high power beam shaping as well as propose a way to improve the diffraction efficiency of such structures by transitioning from a single to multi-layer holograms.}, author = {Alexeev, Ilya and Brehm, Eric and Nendel, Florian and Strauß, Johannes and Baum, Marcus and Schmidt, Michael}, doi = {10.2961/jlmn.2016.02.0019}, faupublication = {yes}, journal = {Journal of Laser Micro Nanoengineering}, keywords = {phase only holograms, ultrafast ablation, ITO nanoparticles, beam shaping}, pages = {261-265}, peerreviewed = {Yes}, title = {{Fabrication} and {Application} of {Phase} only {Holograms} for {High} {Power} {Laser} {Beam} {Shaping}}, volume = {11}, year = {2016} } @article{faucris.124084664, abstract = {
Accurate positioning of a sample is one of the major challenges in the laser micro manufacturing – especially if the requirements on tolerances are high as in ultrafast laser micromachining. There are a number of methods that allow detection of the surface position, however only few of them use the beam of the processing laser as a basis for the measurement. These methods have an advantage that any changes in the structuring beam will be inherently accommodated for. This work describes a direct contact free method to accurately determine the surface position with respect to the structuring beam focal plane. The method makes alignment of unique samples precise and time efficient due to ease of automation and provides a reproducibility of surface detection of less than 1 μm.
}, author = {Strauß, Johannes and Cvecek, Kristian and Gröschl, Andreas Christian and Alexeev, Ilya and Schmidt, Michael}, doi = {10.1016/j.phpro.2012.10.103}, faupublication = {yes}, journal = {Physics Procedia}, keywords = {sample alignment; laser focus positioning; varying sample positioning}, pages = {800-806}, peerreviewed = {Yes}, title = {{Focus} {Alignment} {Method} for {Laser} {Manufacturing} at {Sub}-micron {Positional} {Accuracy}}, volume = {39}, year = {2012} } @article{faucris.111843644, abstract = {The spectral dispersion of ultrashort pulses allows the simultaneous focusing of light in both space and time, which creates so-called spatiotemporal foci. Such space–time coupling may be combined with the existing holographic techniques to give a further dimension of control when generating focal light fields. In the present study, it is shown that a phase-only hologram placed in the pupil plane of an objective and illuminated by a spatially chirped ultrashort pulse can be used to generate three-dimensional arrays of spatio-temporally focused spots. By exploiting the pulse front tilt generated at focus when applying simultaneous spatial and temporal focusing (SSTF), it is possible to overlap neighboring foci in time to create a smooth intensity distribution. The resulting light field displays a high level of axial confinement, with experimental demonstrations given through two-photon microscopy and the non-linear laser fabrication of glass.}, author = {Sun, Bangshan and Salter, Patrick and Roider, Clemens and Jesacher, Alexander and Strauß, Johannes and Heberle, Johannes and Schmidt, Michael and Booth, Martin J.}, doi = {10.1038/lsa.2017.117}, faupublication = {yes}, journal = {Light: Science & Applications}, keywords = {Micro-optics; Nonlinear optics; Ultrafast photonics}, month = {Jan}, peerreviewed = {Yes}, title = {{Four}-dimensional light shaping: manipulating ultrafast spatiotemporal foci in space and time}, volume = {7}, year = {2018} } @article{faucris.123394524, abstract = {Phase holograms offer great potential e.g. for laser beam shaping and imaging applications. However, the generation of these structures typically requires multi-step processes which tend to be time-consuming and expensive, especially if high-quality structures are required. In this work we demonstrate a flexible and inexpensive method which allows for the production of binary phase-only holograms by laser ablation of ITO nanoparticle layers. Since these layers are ablated free of residues, accurately defined phase shifts can be achieved. While arbitrarily shaped structures can be generated, the ITO layer thickness can be adjusted in order to freely tune the phase shift for the desired wavelength. In the diffraction patterns generated by the holograms we observed an excellent zero order suppression.}, author = {Baum, Marcus and Strauß, Johannes and Grüßel, Felix and Alexeev, Ilya and Schmidt, Michael}, doi = {10.1088/2040-8978/16/12/125706}, faupublication = {yes}, journal = {Journal of Optics}, keywords = {hologram; binary; ITO; thin film; laser; ablation; nanoparticle}, pages = {125706}, peerreviewed = {Yes}, title = {{Generation} of phase-only holograms by laser ablation of nanoparticulate {ITO} layers}, volume = {16}, year = {2014} } @article{faucris.123366804, abstract = {In this paper we present the fabrication procedure as well as the preliminary experimental results of a novel method for construction of high resolution nanometric interconnection lines. The fabrication procedure relies on a self-assembly process of gold nanoparticles at specific predetermined nanostructures. The nanostructures for the self-assembly process are based on the focused ion beam (FIB) or scanning electron beam (SEM) technology. The assembled nanoparticles are being illuminated using a picosecond laser with a wavelength of 532 nm. Different pulse energies have been investigated. The paper aimed at developing a novel and reliable process for fabrication of interconnection lines encompass three different disciplines, self-assembly of nanometric particles, optics and microelectroni}, author = {Shahmoon, Asaf and Strauß, Johannes and Zafri, Hadar and Schmidt, Michael and Zalevsky, Zeev}, doi = {10.1016/j.phpro.2016.08.153}, faupublication = {yes}, journal = {Physics Procedia}, keywords = {Interconnection lines; nanoparticles; nanofabrication; picosecond laser}, pages = {188-193}, peerreviewed = {Yes}, title = {{High} {Resolution} {Fabrication} of {Interconnection} {Lines} {Using} {Picosecond} {Laser} and {Controlled} {Deposition} of {Gold} {Nanoparticles}}, volume = {83}, year = {2016} } @inproceedings{faucris.114806824, abstract = {Since high-power ultrashort pulsed (usp) laser sources are commercially available, customers are facing the issue of delivering high power appropriately onto their work piece. This results in an inefficient usage of the provided laser power. Current technologies allow either for fast deflection or spatial adaption of the laser beam. To access a fast temporal and spatial distribution of the laser power the use of the acousto optic (AO) effect was proposed and experimentally confirmed. While the usage of AO beam deflection is well known for decades, the application as a beam shaper is subject of current research. This technology is capable to operate at several MHz. Therefore, two orthogonal AO deflectors (AOD) are placed in the Fourier plane of a lens. If a proper acoustic signal is applied synchronized to the laser pulses, each pulse is affected by a quasi-static arbitrary grating. The desired intensity distribution can now be observed in the image plane of the lens. The AO deflectors are driven by a two-channel arbitrary waveform generator followed by an amplifier stage. In this paper we present an algorithm based on an Iterative Fourier Transform Algorithm (IFTA) to calculate the acoustic field from an input intensity distribution. The intensity distribution is projected in x- and y-direction to convert into two separated 1D-profiles. Via the IFTA the necessary phase delays for both directions are calculated. Then the corresponding acoustic signals are computed and hardware restrictions like the modulation bandwidths of the AOD and the signal generators are consider for the iterative optimization. Also the amplifiers amplitude response characteristics are taken into account. The resulting 2D intensity distribution is simulated by convolution of both signals. We present results of intensity distributions by AO beam shaping. The practical restrictions of achievable beam profiles of an AO beam shaping device are discussed. Finally we show micro structures generated by such a device.}, author = {Strauß, Johannes and Vorndran, Martin and Heberle, Johannes and Schmidt, Michael}, booktitle = {International Congress on Applications of Lasers & Electro–Optics}, date = {2016-10-16/2016-10-20}, faupublication = {yes}, peerreviewed = {unknown}, title = {{IFTA} {Calculation} of {Frequency} {Patterns} for {Acousto} {Optical} {Laser} {Beam} {Shaping}}, venue = {San Diego, CA, USA}, year = {2016} } @inproceedings{faucris.109631984, abstract = {
Bei der Mikromaterialbearbeitung mit Ultrakurzpulslasern hat die absolute Bestimmung der Fokuslage zu der Werkstückoberfläche einen großen Einfluss auf das Bearbeitungsergebnis. In dieser Veröffentlichung wird demonstriert wie die von der Werkstückoberfläche reflektierte Laserstrahlung des Bearbeitungslasers mit einem konfokalem Messsystem ausgewertet wird, um so eine relative Positionsbestimmung mit 1/10 der Rayleighlänge durchzuführen. Des Weiteren wird gezeigt wie dieses Messsystem durch die höhere Harmonische, welche an der Oberfläche von Werkstoffen wie Glas erzeugt wird, kalibriert wird und somit eine absolute Positionsbestimmung des Bearbeitungsfokus zur Werkstückoberfläche erreicht wird.
Large-area processing with high material removal rates by ultrashort pulsed (USP) lasers is coming into focus by the development of high-power USP laser systems. However, currently the bottleneck for high-rate production is given by slow and inefficient beam manipulation. On the one hand, slow beam deflection with regard to high pulse repetition rates leads to heat accumulation and shielding effects, on the other hand, a conventional focus cannot provide the optimum fluence due to the Gaussian intensity profile. In this paper, we emphasize on two approaches of dynamic laser beam shaping with liquid crystal on silicon spatial light modulation and acousto-optic beam shaping. Advantages and limitations of dynamic laser beam shaping with regard to USP laser material processing and methods for reducing the influence of speckle are discussed. Additionally, the influence of optics induced aberrations on speckle characteristics is evaluated. Laser material processing results are presented correlating the achieved structure quality with the simulated and measured beam quality. Experimental and analytical investigations show a certain fluence dependence of the necessary number of alternative holograms to realize homogeneous microstructures.
}, author = {Häfner, Tom and Strauß, Johannes and Roider, Clemens and Heberle, Johannes and Schmidt, Michael}, doi = {10.1007/s00339-017-1530-0}, faupublication = {yes}, journal = {Applied Physics A: Materials Science and Processing}, peerreviewed = {Yes}, title = {{Tailored} laser beam shaping for efficient and accurate microstructuring}, url = {https://link.springer.com/article/10.1007/s00339-017-1530-0}, volume = {124}, year = {2018} } @article{faucris.108957904, abstract = {High-power ultrashort pulsed lasers with average powers exceeding 100 W are commercially available. Yet, the successful transfer of such lasers into application, microstructuring in particular, lacks appropriate tools. The most promising strategies today are high-speed beam scanning or parallelization in terms of beam shaping or multi-spot generation. A combination of both strategies into one device would be the most promising tool to reach much higher processing efficiencies compared to date. We will present the first sub-steps we are undertaking to realize such devices, utilizing the acoustooptic effect as well as liquid crystal based modulators and phase holograms. First results include the rapid manufacturing of phase holograms and high-speed beam scanning and shaping using acoustooptical deflectors - reaching beam shape switching times of 1 mu s.}, author = {Baum, Marcus and Bechtold, Peter and Strauß, Johannes and Schmidt, Michael}, doi = {10.2961/jlmn.2015.02.0020}, faupublication = {yes}, journal = {Journal of Laser Micro Nanoengineering}, keywords = {Beam shaping;holography;spatial light modulator;acoustooptic;ultrashort;ITO}, pages = {216-221}, peerreviewed = {Yes}, title = {{Towards} {Dynamic} {Holographic} {Laser} {Beam} {Shaping}}, volume = {10}, year = {2015} }