@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{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{VerpoortBittnerWittrock2020,
  author    = {Verpoort, Sven and Bittner, Matthias and Wittrock, Ulrich},
  title     = {Fast focus-shifter based on a unimorph deformable mirror},
  series = {Applied Optics},
  volume    = {59},
  journal   = {Applied Optics},
  number    = {23},
  organization    = {Optical Society of America},
  issn      = {1559-128X},
  doi       = {10.1364/AO.397495},
  pages     = {6959 -- 6965},
  year      = {2020},
  abstract  = {On-the-fly remote laser processing plays an increasingly important role in modern fabrication techniques. These processes require guiding of the focus of a laser beam along the contours of the workpiece in three dimensions. State-of-the-art galvanometer scanners already provide highly dynamic and precise transverse x-y beam steering. However, longitudinal focus shifting ("z-shifting") relying on conventional optics is restricted to a bandwidth of a few hundred Hz. We have developed and manufactured a fast piezo-based z-shifting mirror with diffraction-limited surface fidelity providing a focus shift of 1z> 60 mm with an actuation rate of 2 kHz.},
  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{VerpoortWittrock2010,
  author    = {Verpoort, Sven and Wittrock, Ulrich},
  title     = {Actuator patterns for unimorph and bimorph deformable mirrors},
  series = {Appl. Opt.},
  volume    = {49},
  journal   = {Appl. Opt.},
  publisher = {OSA},
  doi       = {10.25974/fhms-649},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6490},
  pages     = {G37 -- G46},
  year      = {2010},
  abstract  = {The actuator pattern of an adaptive mirror determines the amplitudes and the fidelities of the mirror deformations that can be achieved. In this study, we analyze and compare different electrode patterns of piezoelectric unimorph deformable mirrors using a numerical finite element model. The analysis allows us to determine the optimum actuator pattern, and it is also applicable to bimorph mirrors. The model is verified by comparing its predictions with experimental results of our prototype of a novel unimorph deformable mirror.},
  language  = {de}
}
@article{RauschVerpoortWittrock2015,
  author    = {Rausch, Peter and Verpoort, Sven and Wittrock, Ulrich},
  title     = {Unimorph deformable mirror for space telescopes: design and manufacturing},
  series = {Opt. Expr.},
  volume    = {23},
  journal   = {Opt. Expr.},
  doi       = {10.25974/fhms-822},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8227},
  pages     = {19469 -- 19477},
  year      = {2015},
  abstract  = {Large space telescopes made of deployable and lightweight structures suffer from aberrations caused by thermal deformations, gravitational release, and alignment errors which occur during the deployment procedure. An active optics system would allow on-site correction of wave-front errors, and ease the requirements on thermal and mechanical stability of the optical train. In the course of a project funded by the European Space Agency we have developed and manufactured a unimorph deformable mirror based on piezoelectric actuation. The mirror is able to work in space environment and is designed to correct for large aberrations of low order with high surface fidelity. This paper discusses design, manufacturing and performance results of the deformable mirror.},
  language  = {en}
}
@article{RauschVerpoortWittrock2016,
  author    = {Rausch, Peter and Verpoort, Sven and Wittrock, Ulrich},
  title     = {Unimorph deformable mirror for space telescopes: environmental testing},
  series = {Opt. Expr.},
  volume    = {24},
  journal   = {Opt. Expr.},
  doi       = {10.25974/fhms-853},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8530},
  pages     = {1528 -- 1542},
  year      = {2016},
  abstract  = {We have developed and manufactured a unimorph deformable mirror for space telescopes based on piezoelectric actuation. The mirror features 44 actuators, has an aperture of 50 mm, and is designed to reproduce low-order Zernike modes with a stroke of several tens of µm. We assessed the space compliance by operating the mirror in thermal vacuum, and exposing it to random and sinusoidal vibrations, as well as to ionizing irradiation. Additionally, the operational life time and the laser power handling capability were tested. The mirror was successfully operated in thermal vacuum at 100 K. We report on the conducted tests and the methods used to evaluate the mirror\&\#180;s performance, and discuss the compliance with the demanded requirements},
  language  = {de}
}