@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}
}
@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}
}
@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{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}
}