@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}
}
@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}
}
@article{Wittrock2010,
  author    = {Wittrock, Ulrich},
  title     = {Laryngeally echolocating bats (Brief Communication Arising)},
  series = {Nature},
  volume    = {466},
  journal   = {Nature},
  doi       = {10.1038/nature09156},
  pages     = {E6},
  year      = {2010},
  language  = {mul}
}
@incollection{VerpoortWittrock2009,
  author    = {Verpoort, Sven and Wittrock, Ulrich},
  title     = {Miniaturized adaptive mirror for solid state laser resonators},
  series = {Proceedings of the 7th International Workshop on Adaptive Optics for Industry and Medicine, Shatura, Russia},
  booktitle = {Proceedings of the 7th International Workshop on Adaptive Optics for Industry and Medicine, Shatura, Russia},
  year      = {2009},
  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{Wittrock2014,
  author    = {Wittrock, Ulrich},
  title     = {Grenzen? Welche Grenzen? Prof. Ulrich Wittrock, Leiter des Labors f{\"u}r Photonik an der Fachhochschule M{\"u}nster, fragt nach den ultimativen Grenzen der Lasertechnik},
  series = {Laser Community - das Lasermagazin von Trumpf},
  volume    = {02:14},
  journal   = {Laser Community - das Lasermagazin von Trumpf},
  year      = {2014},
  language  = {de}
}
@article{Wittrock2014,
  author    = {Wittrock, Ulrich},
  title     = {Limitations? What Limitations? Prof. Ulrich Wittrock, head of the Photonics Laboratory at the M{\"u}nster University of Applied Sciences, seeks out the ultimate boundaries of laser technology},
  series = {Laser Community - the laser magazine from Trumpf},
  volume    = {02:14},
  journal   = {Laser Community - the laser magazine from Trumpf},
  year      = {2014},
  language  = {en}
}
@inproceedings{VerpoortWittrock2011,
  author    = {Verpoort, Sven and Wittrock, Ulrich},
  title     = {Deformable mirrors for high power lasers},
  series = {Proceedings of the 8th International Workshop on Adaptive Optics for Industry and Medicine (AOIM)},
  booktitle = {Proceedings of the 8th International Workshop on Adaptive Optics for Industry and Medicine (AOIM)},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-106953},
  year      = {2011},
  abstract  = {It has been shown that the beam quality and the efficiency of high-power solid-state lasers could be enhanced by the use of deformable mirrors in order to compensate for optical aberrations. An intracavity compensation requires a deformable mirror which is capable of handling very high laser intensities. The active diameter of the deformable mirror should be a few millimeters in order to match typical fundamental mode laser beam diameters. There is a wide variety of commercially available deformable mirrors, but neither meets all requirements.},
  language  = {en}
}
@inproceedings{KazasidisVerpoortWittrock2019,
  author    = {Kazasidis, Orestis and Verpoort, Sven and Wittrock, Ulrich},
  title     = {Image-based wavefront correction for space telescopes},
  series = {International Conference on Space Optics - ICSO 2018},
  booktitle = {International Conference on Space Optics - ICSO 2018},
  publisher = {Proc. SPIE},
  doi       = {10.1117/12.2536206},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-109036},
  pages     = {111807Z},
  year      = {2019},
  abstract  = {With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control variables. In severely aberrated systems, the Zernike modes are not orthogonal to each other with respect to this merit function. Using wavefront maps, the PSF, and the MTF, we discuss the physical causes for the non-orthogonality of the Zernike modes with respect to the merit function. We show that for combinations of Zernike modes with the same azimuthal order, a flatter wavefront in the central region of the aperture is more important than the RMS wavefront error across the full aperture for achieving a better merit function. The non-orthogonality of the Zernike modes with respect to the merit function should be taken into account when designing the algorithm for image-based wavefront correction, because it may slow down the process or lead to premature convergence.},
  language  = {en}
}