TY  - JOUR
A1  - Kazasidis, Orestis
A1  - Verpoort, Sven
A1  - Soloviev, Oleg
A1  - Vdovin, Gleb
A1  - Verhaegen, Michel
A1  - Wittrock, Ulrich
T1  - Extended-image-based correction of aberrations using a deformable mirror with hysteresis
JF  - Opt. Expr.
N2  - 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.
KW  - active optics, metrics, aberration compensation
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-14759
UR  - https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-26-21-27161&id=398820
VL  - 26
SP  - 27161
EP  - 27178
ER  - 
TY  - JOUR
A1  - Kazasidis, Orestis
A1  - Verpoort, Sven
A1  - Wittrock, Ulrich
T1  - Aberration balancing using an image-sharpness metric
JF  - J. Opt. Soc. Am. A
N2  - 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.
KW  - adaptive optics; image-sharpness
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-109198
UR  - https://www.osapublishing.org/josaa/abstract.cfm?uri=josaa-36-8-1418
VL  - 36
IS  - 8
SP  - 1418
EP  - 1422
ER  - 
TY  - JOUR
A1  - Kazasidis, Orestis
A1  - Wittrock, Ulrich
T1  - Interferometric measurement of the temperature coefficient of the refractive index dn/dT and the coefficient of thermal expansion of Pr:YLF laser crystals
JF  - Opt. Expr.
N2  - We report interferometric measurements of the temperature coefficient of the refractive index (dn=dT) and the coefficient of thermal expansion (a) of a praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystal and of a fused silica reference sample. Our phase-resolved interferometric method yields a large number of data points and thus allows a precise measurement and a good error estimation. Furthermore, both dn=dT and a are obtained simultaneously from a single measurement which reduces errors that can occur in separate measurements. Over the temperature range from 20 °C to 80 °C, the value of dn=dT of Pr:YLF decreases from -5.2 x 10-6 /K to -6.2 x 10-6 /K for the ordinary refractive index and from -7.6 x 10-6 /K to -8.6 x 10-6 /K for the extraordinary refractive index. The coefficient of thermal expansion for the a-axis of Pr:YLF increases from 16.4 x 10-6 /K to 17.8 x 10-6 /K over the same temperature range.
KW  - refractive index change
KW  - thermal expansion coefficient
KW  - laser crystal
KW  - praseodymium
KW  - yttrium lithium fluoride
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-7720
VL  - 22
SP  - 30683
EP  - 30696
PB  - Optical Society of America
ER  -