@article{KazasidisVerpoortWittrock2019, author = {Kazasidis, Orestis and Verpoort, Sven and Wittrock, Ulrich}, title = {Aberration balancing using an image-sharpness metric}, series = {J. Opt. Soc. Am. A}, volume = {36}, journal = {J. Opt. Soc. Am. A}, number = {8}, doi = {10.1364/JOSAA.36.001418}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-109198}, pages = {1418 -- 1422}, year = {2019}, abstract = {Image-sharpness metrics can be used to optimize optical systems and to control wavefront sensorless adaptive optics systems. We show that for an aberrated system, the numerical value of an image-sharpness metric can be improved by adding specific aberrations. The optimum amplitudes of the additional aberrations depend on the power spectral density of the spatial frequencies of the object.}, language = {en} } @article{KazasidisVerpoortWittrock2020, author = {Kazasidis, Orestis and Verpoort, Sven and Wittrock, Ulrich}, title = {Sensor for dynamic focus control of a deformable mirror}, series = {Appl. Opt.}, journal = {Appl. Opt.}, number = {59}, doi = {10.1364/AO.392970}, pages = {5625 -- 5630}, year = {2020}, abstract = {We recently presented a novel unimorph deformable mirror which allows for dynamic focus shift with an actuation rate of 2 kHz. Such mirrors suffer from hysteresis and creep. Therefore, they have to be operated in closed-loop. For this purpose, we developed a defocus sensor based on an astigmatic detection system. In this paper, we present the sensor design and discuss its performance.}, language = {en} } @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{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{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{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{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} } @article{AlonsoAlpigianiWittrock2022, author = {Alonso, Iv{\´a}n and Alpigiani, Cristiano and Wittrock, Ulrich}, title = {Cold atoms in space: community workshop summary and proposed road-map}, series = {EPJ Quantum Technology}, journal = {EPJ Quantum Technology}, publisher = {Springer Nature}, doi = {10.1140/epjqt/s40507-022-00147-w}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-160413}, pages = {30}, year = {2022}, abstract = {We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.}, language = {en} } @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} }