@book{OPUS4-1746, title = {Adaptive optics for industry and medicine. Proceedings of the 4th International Workshop on Adaptive Optics for Industry and Medicine}, editor = {Wittrock, Ulrich}, publisher = {Springer}, address = {Berlin}, isbn = {3-540-23978-2}, pages = {398}, year = {2005}, language = {en} } @misc{OPUS4-4711, title = {6th Laser Ceramics Symposium}, series = {Opt. Mat.}, volume = {34}, journal = {Opt. Mat.}, editor = {Wittrock, Ulrich and Kynast, Ulrich and J{\"u}stel, Thomas and Bredol, Michael}, publisher = {Elsevier B.V.}, pages = {935 -- 1002}, year = {2012}, language = {mul} } @article{AlbersWittrock2011, author = {Albers, Klaus and Wittrock, Ulrich}, title = {Optical pump concepts for highly efficient quasi-three-level lasers}, series = {Appl. Phys. B}, volume = {105}, journal = {Appl. Phys. B}, publisher = {Springer}, doi = {10.25974/fhms-646}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6467}, pages = {245 -- 254}, year = {2011}, abstract = {Efficient quasi-three-level laser operation requires the generation of the highest possible pump rate from a given pump source. We derive the fundamental scaling laws for the pump rate and we extract optimization criteria for pump concepts from these laws. The analysis is then applied to the thin-disk laser. Based on the results, a novel pump concept for thin-disk lasers is proposed, which allows for several tens of pump beam passes and reduces the optical complexity of conventional pump concepts. Furthermore, the beam quality of the pump source is preserved almost completely, facilitating the highest possible pump rate.}, language = {en} } @article{BuskeWittrock2006, author = {Buske, Ivo and Wittrock, Ulrich}, title = {Diffraction analysis of aberrated laser resonators}, series = {Appl. Phys. B}, volume = {83}, journal = {Appl. Phys. B}, doi = {10.25974/fhms-825}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8252}, pages = {229 -- 233}, year = {2006}, abstract = {A numerical analysis of laser resonators with aberrations is presented. {T}he analysis shows that aberrations lead to large diffraction losses of laser resonators which are laid out to produce diffraction-limited beam quality. {S}tatic or dynamic compensation of the aberrations is possible and would yield much higher output power.}, language = {en} } @inproceedings{DurandAmiauxSauvageetal.2016, author = {Durand, G. and Amiaux, J. and Sauvage, M. and Austin, J. and Chesne, S. and Collette, C. and Helgouashl, S. and Pareschi, J. and Penfornis, Y. and Valsecchi, G. and Wittrock, U.}, title = {TALC a far-infrared 20m space telescope and the ELICSIR consortium to reach TRL 3}, series = {Proceedings of the 37th ESA Antenna Workshop, Noordwijk, Netherlands}, booktitle = {Proceedings of the 37th ESA Antenna Workshop, Noordwijk, Netherlands}, doi = {10.25974/fhms-925}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-9253}, year = {2016}, abstract = {Further space exploration in the far-infrared (FIR) requires larger apertures in order to improve the spatial resolution of captured images. To this purpose, the Thinned Aperture Light Collector (TALC) concept of a deployable annular telescope has been recently developed at CEA, which offers novel perspectives for FIR space missions. The consortium ELICSIR consortium of European institutes and companies has been created to improve the technological readiness level (TRL) of its key systems and components.}, language = {en} } @inproceedings{FreudlingGrzesikErhardetal.2021, author = {Freudling, Maximilian and Grzesik, Andreas and Erhard, Markus and Gerhards, Maximilian and Leitz, Sinje and Verpoort, Sven and Wittrock, Ulrich and Hallibert, Pascal}, title = {Space-qualified piezo based deformable mirror for future instruments with active optics}, series = {Proceedings of the International Conference on Space Optics (ICSO)}, volume = {11852}, booktitle = {Proceedings of the International Conference on Space Optics (ICSO)}, organization = {ESA/ESTEC, Noordwijk}, doi = {10.25974/fhms-13741}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-137410}, pages = {1185231-11}, year = {2021}, abstract = {This paper presents the results of the technology development project "Enabling Technologies for Piezo-Based Deformable Mirrors in Active Optics Correction Chains" conducted by OHB System AG together with its partner M{\"u}nster University of Applied Sciences (MUAS). The project was funded by ESA within their General Support Technology Programme (GSTP). We address in this paper mainly the definition, flow-down and verification of the requirements for the Deformable Mirror (DM). The requirements were derived from a set of real space mission applications. The deformation of the mirror is performed by piezo-ceramic actuators in an unimorph configuration. The finally developed DM is able produce Zernike modes with a stroke of several tens of µm over a clear optical aperture of 50 mm in diameter. It underwent successfully a full environmental qualification campaign including thermal cycling, shock- and vibration testing, as well as exposure to proton and γ-ray radiation. Thermal and performance tests were performed in the temperature range from 100 K to 300 K. Furthermore, the DM sustained all vibration (random 17.8 g RMS and sinus) and shock (300 g) testing. Thereby all criticalities which were identified a previous study have been overcome successfully. A Technology Readiness Level (TRL) of 5 is reached, as the component has been validated in relevant environment. Based on the high level of maturity, this deformable mirror is now ready for the incorporation in future flight instruments. The achieved TRL of 5 is sufficient for the status of a PDR at payload level and gives thus a very good basis for all kinds of potential B2, C/D payload developments.}, language = {en} } @article{HeuckNeumayerKuehletal.2006, author = {Heuck, Hans-Martin and Neumayer, Paul and K{\"u}hl, Thomas and Wittrock, Ulrich}, title = {Chromatic aberration in petawatt-class lasers}, series = {Appl. Phys. B}, volume = {84}, journal = {Appl. Phys. B}, publisher = {Springer}, doi = {10.25974/fhms-652}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6523}, pages = {421 -- 428}, year = {2006}, abstract = {In order to avoid optical damage and non-linear effects, high-power, high-energy lasers of the petawatt class like PHELIX (petawatt high-energy laser for heavy-ion experiments) use large-aperture optics. Usually, chromatic aberration associated with these optical elements is neglected. By means of numerical simulations, we show how the chromatic aberration affects the focal intensity pattern. In particular, we make quantitative predictions of how chromatic aberration decreases the focused peak intensity. Furthermore, we prove the feasibility of a new interferometer that measures the temporal pulse front distortions which arise from expansion telescopes. We also propose a scheme that pre-compensates these distortions.}, language = {en} } @inproceedings{HeuckWittrockFilsetal.2007, author = {Heuck, Hans-Martin and Wittrock, Ulrich and Fils, J{\´e}rome and Borneis, Stefan and Witte, Klaus and Eisenbart, Udo and Javorkova, Dasa and Bagnoud, Vincent and G{\"o}tte, Stefan and Tauschwitz, Andreas and Onkels, Eckehard}, title = {Adaptive optics at the PHELIX laser}, series = {Adaptive Optics for Laser Systems and Other Applications, Proc. SPIE}, volume = {6584}, booktitle = {Adaptive Optics for Laser Systems and Other Applications, Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-621}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6215}, pages = {658402}, year = {2007}, abstract = {GSI Darmstadt currently builds a high-energy petawatt Nd:glass laser system, called PHELIX (Petawatt High-Energy Laser for Heavy-Ion Experiments). PHELIX will offer the world-wide unique combination of a high current, high-energy heavy-ion beam with an intense laser beam. Aberrations due to the beam transport and due to the amplification process limit the focusability and the intensity at the target. We have investigated the aberrations of the different amplification stages. The pre-amplifier stage consists of three rod-amplifiers which cause mainly defocus, but also a small part of coma and astigmatism. The main amplifier consists of five disk amplifiers with a clear aperture of 315 mm. These large disk-amplifiers cause pump-shot aberrations which occur instantly. After a shot, the disk amplifiers need a cooling time of several hours to relax to their initial state. This limits the repetition rate and causes long-term aberrations. We will present first measurements of the pump-shot and long-term aberrations caused by the pre- and the main amplifier in a single-pass configuration. In this context, we will present the adaptive optics system which is implemented in the PHELIX beam line and discuss its capability to compensate for the pump-shot and long-term aberrations.}, language = {de} } @article{KazasidisVerpoortSolovievetal.2018, author = {Kazasidis, Orestis and Verpoort, Sven and Soloviev, Oleg and Vdovin, Gleb and Verhaegen, Michel and Wittrock, Ulrich}, title = {Extended-image-based correction of aberrations using a deformable mirror with hysteresis}, series = {Opt. Expr.}, volume = {26}, journal = {Opt. Expr.}, doi = {10.1364/OE.26.027161}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-14759}, pages = {27161 -- 27178}, year = {2018}, abstract = {With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a high-resolution imaging testbed to evaluate control algorithms. In this paper we use an algorithm based on the heuristic hill climbing technique and compare the correction in three different domains, namely the voltage domain, the domain of the Zernike modes, and the domain of the singular modes of the deformable mirror. Through our systematic experimental study, we found that successive control in two domains effectively counteracts uncompensated hysteresis of the deformable mirror.}, language = {en} } @inproceedings{KazasidisVerpoortWittrock2018, author = {Kazasidis, Orestis and Verpoort, Sven and Wittrock, Ulrich}, title = {Algorithm design for image-based wavefront control without wavefront sensing}, series = {SPIE Optical Instrument Science, Technology, and Applications, Proc. SPIE}, volume = {10695}, booktitle = {SPIE Optical Instrument Science, Technology, and Applications, Proc. SPIE}, doi = {10.1117/12.2312523}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-14760}, pages = {1069502}, year = {2018}, abstract = {Active optics is an enabling technology for future large space telescopes. Image-based wavefront control uses an image-sharpness metric to evaluate the optical performance. A control algorithm iteratively adapts a corrective element to maximize this metric, without reconstructing the wavefront. We numerically study a sharpness metric in the space of Zernike modes, and reveal that for large aberrations the Zernike modes are not orthogonal with respect to this metric. The findings are experimentally verified by using a unimorph deformable mirror as corrective element. We discuss the implications for the correction process and the design of control algorithms.}, language = {en} }