TY - JOUR A1 - Trinschek, Sarah A1 - Vorholt, Christian A1 - Wittrock, Ulrich T1 - Nonlinear dynamics in intra-cavity pumped thin-disk lasers JF - Optics Express N2 - Cross-saturation of the gain media in intra-cavity pumped lasers leads to complex dynamics of the laser power. We present experimental results and a detailed theoretical analysis of this nonlinear dynamics for an intra-cavity pumped Yb:YAG thin-disk laser in the framework of a rate-equation model. The gain medium of this laser is residing in the resonator of a conventional, diode-pumped Yb:YAG thin-disk laser. Continuous-wave operation, periodic pulse trains, and chaotic fluctuations of the optical power of both lasers were observed. The dynamics is not driven by external perturbations but arises naturally in this laser system. Further examination revealed that these modes of operation can be controlled by the resonator length of the diode-pumped laser but that the system can also show hysteresis and multi-stability. Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-132355 UR - https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-4-5755&id=447544 VL - 29 IS - 4 SP - 5755 EP - 5773 ER - TY - CHAP A1 - Leitz, Sinje A1 - Gerhards, Maximilian A1 - Verpoort, Sven A1 - Wittrock, Ulrich A1 - Freudling, Maximilian A1 - Grzesik, Andreas A1 - Erhard, Markus A1 - Hallibert, Pascal T1 - Vibration and shock testing of a 50 mm aperture unimorph deformable mirror T2 - Proceedings of the International Conference on Space Optics (ICSO) N2 - We present our latest results on a refined unimorph deformable mirror which was developed in the frame of the ESA GSTP activity ”Enabling Technologies for Piezo-Based Deformable Mirrors in Active Optics Correction Chains”. The identified baseline concept with the soft piezoceramic material PIC151 successfully sustained all vibration requirements (17.8 gRMS random and 20 g sine) and shock testing (300 g SRS). We cover the mirror design development which reduces the stress in the brittle piezo-ceramic by 90 % compared to the design from a former GSTP activity. We briefly address the optical characterization of the deformable mirror, namely the achieved Zernike amplitudes as well as the unpowered surface deformation (1.7 µm) and active flattening (12.3 nmRMS). The mirror produces low-order Zernike modes with a stroke of several tens of micrometer over a correction aperture of 50 mm, which makes the mirror a versatile tool for space telescopes. KW - active optics KW - adaptive optics KW - deformable mirror KW - vibration damping KW - space telescopes Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-137401 UR - https://icso2020.com/ VL - 11852 SP - 118524N ER - TY - CHAP A1 - Freudling, Maximilian A1 - Grzesik, Andreas A1 - Erhard, Markus A1 - Gerhards, Maximilian A1 - Leitz, Sinje A1 - Verpoort, Sven A1 - Wittrock, Ulrich A1 - Hallibert, Pascal T1 - Space-qualified piezo based deformable mirror for future instruments with active optics T2 - Proceedings of the International Conference on Space Optics (ICSO) N2 - 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 Münster 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. KW - deformable mirror KW - active optics KW - space qualification KW - space telescopes KW - adaptive optics Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-137410 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11852/1185231/Space-qualified-Piezo-Based-Deformable-Mirror-for-future-Instruments-with/10.1117/12.2599467.full VL - 11852 SP - 1185231-11 ER - TY - CHAP A1 - Kazasidis, Orestis A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Image-based wavefront correction for space telescopes T2 - International Conference on Space Optics - ICSO 2018 N2 - 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. KW - active optics, adaptive optics, sharpness metrics, aberration compensation, algorithm design Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-109036 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11180/111807Z/Image-based-wavefront-correction-for-space-telescopes/10.1117/12.2536206.full?SSO=1 SP - 111807Z PB - Proc. SPIE 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 - 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 - CHAP A1 - Kazasidis, Orestis A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Algorithm design for image-based wavefront control without wavefront sensing T2 - SPIE Optical Instrument Science, Technology, and Applications, Proc. SPIE N2 - 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. KW - active optics, adaptive optics, sharpness metrics, aberration compensation, algorithm design Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-14760 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10695/1069502/Algorithm-design-for-image-based-wavefront-control-without-wavefront-sensing/10.1117/12.2312523.full VL - 10695 SP - 1069502 ER - TY - JOUR A1 - Vorholt, Christian A1 - Wittrock, Ulrich T1 - Single-frequency oscillation of thin-disk lasers due to phase-matched pumping JF - Opt. Expr. N2 - We present a novel pump concept that should lead to single-frequency operation of thin-disk lasers without the need for etalons or other spectral filters. The single-frequency operation is due to matching the standing wave pattern of partially coherent pump light to the standing wave pattern of the laser light inside the disk. The output power and the optical efficiency of our novel pump concept are compared with conventional pumping. The feasibility of our pump concept was shown in previous experiments. KW - diode-pumped laser KW - solid-state laser KW - ytterbium laser Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-10258 VL - 25 SP - 21388 EP - 21399 ER - TY - JOUR A1 - Rausch, Peter A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Unimorph deformable mirror for space telescopes: environmental testing JF - Opt. Expr. N2 - 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´s performance, and discuss the compliance with the demanded requirements KW - active or adaptive optics KW - telescopes thermal effects vibration analysis KW - radiation KW - space optics KW - space instrumentation Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-8530 VL - 24 SP - 1528 EP - 1542 ER - TY - CHAP A1 - Rausch, Peter A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Unimorph piezoelectric deformable mirrors for space telescopes T2 - Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, Proc. SPIE N2 - We have developed, manufactured and tested a unimorph deformable mirror for space applications based on piezoelectric actuation. The mirror was designed for the correction of low-order Zernike modes with a stroke of several tens of micrometers over a clear aperture of 50 mm. It was successfully tested in thermal vacuum, underwent lifetime tests, and was exposed to random vibrations, sinusoidal vibrations, and to ionizing radiation. We report on design considerations, manufacturing of the mirror, and present the test results. Furthermore, we discuss critical design parameters, and how our mirror could be adapted to serve recently proposed space telescopes such as HDST and TALC. Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-9230 VL - 9904 SP - 990468 ER -