@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} } @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} } @inproceedings{LeitzGerhardsVerpoortetal.2021, author = {Leitz, Sinje and Gerhards, Maximilian and Verpoort, Sven and Wittrock, Ulrich and Freudling, Maximilian and Grzesik, Andreas and Erhard, Markus and Hallibert, Pascal}, title = {Vibration and shock testing of a 50 mm aperture unimorph deformable mirror}, series = {Proceedings of the International Conference on Space Optics (ICSO)}, volume = {11852}, booktitle = {Proceedings of the International Conference on Space Optics (ICSO)}, organization = {ESA/ESTEC, Noordwijk}, doi = {10.25974/fhms-13740}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-137401}, pages = {118524N}, year = {2021}, abstract = {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.}, language = {en} } @inproceedings{FreudlingGrzesikErhardetal.2021, author = {Freudling, Maximilian and Grzesik, Andreas and Erhard, Markus and Gerhards, Maximilian and Leitz, Sinje and Verpoort, Sven and Wittrock, Ulrich and Hallibert, Pascal}, title = {Space-qualified piezo based deformable mirror for future instruments with active optics}, series = {Proceedings of the International Conference on Space Optics (ICSO)}, volume = {11852}, booktitle = {Proceedings of the International Conference on Space Optics (ICSO)}, organization = {ESA/ESTEC, Noordwijk}, doi = {10.25974/fhms-13741}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-137410}, pages = {1185231-11}, year = {2021}, abstract = {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 M{\"u}nster 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.}, language = {en} } @inproceedings{WittrockWelp2006, author = {Wittrock, Ulrich and Welp, Petra}, title = {Adaptive laser resonator control with deformable MOEMS mirrors}, series = {MEMS/MOEMS Components and Their Applications III, Proc. SPIE}, volume = {6113}, booktitle = {MEMS/MOEMS Components and Their Applications III, Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-653}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6537}, pages = {61130C}, year = {2006}, abstract = {Adaptive laser resonators with deformable MOEMS mirrors under closed-loop control are discussed and experimental results are presented. The requirements for deformable mirrors and for closed-loop control systems of these mirrors are analyzed. Several deformable mirrors have been characterized and the results are presented. Currently available membrane mirrors deform under laser load and need further development before they can be used for aberration correction of solid state lasers above some tens of Watts. Nevertheless, the results are encouraging and the requirements are within reach of currently available technology. Finally, we demonstrate an Nd.YVO4-laser with a closed-loop adaptive resonator and more than 6 W of output power. The closed-loop system was able to compensate artificially introduced aberrations from a phase plate.}, language = {de} } @inproceedings{VerpoortWittrock2011, author = {Verpoort, Sven and Wittrock, Ulrich}, title = {Novel unimorph deformable mirror with monolithic tip-tilt functionality for solid state lasers}, series = {MEMS Adaptive Optics V, Proc. SPIE}, volume = {7931}, booktitle = {MEMS Adaptive Optics V, Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-647}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6471}, pages = {793107}, year = {2011}, abstract = {We present a new type of unimorph deformable mirror with monolithic tip-tilt functionality. The tip-tilt actuation is based on a spiral arm design. The mirror will be used in high-power laser resonators for real-time intracavity phase control. The additional tip-tilt correction with a stroke up to 6 μm simplifies the resonator alignment significantly. The mirror is optimized for a laser beam footprint of about 10 mm. We have modeled and optimized this mirror by finite element calculations and we will present design criteria and tradeoffs for this mirrors. The mirror is manufactured from a super-polished glass substrate with very low surface scattering and excellent dielectric coating.}, language = {en} } @inproceedings{VerpoortWittrock2010, author = {Verpoort, Sven and Wittrock, Ulrich}, title = {Unimorph deformable mirror for telescopes and laser applications in space}, series = {International Conference on Space Optics (ICSO), Rhodes Island, Greece}, booktitle = {International Conference on Space Optics (ICSO), Rhodes Island, Greece}, publisher = {SPIE}, doi = {10.25974/fhms-648}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6484}, year = {2010}, abstract = {Over the past 5 years we have developed a new type of unimorph deformable mirror. The main advantages of this mirror technology are · very low surface scattering due to the use of superpolished glass · excellent coatings, even suitable for high power lasers, can be applied · active diameter of the mirrors can be between 10 mm and 100 mm · large strokes can be achieved even for small mirror diameters · integrated monolithic tip/tilt functionality based on a spiral arm design We have modeled these mirrors by analytical models as well as by the finite element method. This allows us to quickly design new mirrors tailored to specific applications. One example is a mirror for laser applications that has a diameter of 10 mm and can achieve a stroke in defocus mode of 5 μm. The stroke for these mirrors scales as the square of the mirror diameter, meaning that we can achieve, for example, a stroke of 125 μm for a mirror of 50 mm diameter. We will present design criteria and tradeoffs for these mirrors. We characterize our mirrors by the maximum stroke they can deliver for various Zernike modes, under the boundary condition that the Zernike mode has to be created with a certain fidelity, usually defined by the Mar{\´e}chal criterion.}, language = {en} } @inproceedings{VerpoortWelpWittrock2009, author = {Verpoort, Sven and Welp, Petra and Wittrock, Ulrich}, title = {Novel unimorph deformable mirror for solid state laser resonators}, series = {MEMS Adaptive Optics III, Proc. SPIE}, volume = {72090N}, booktitle = {MEMS Adaptive Optics III, Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-650}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6504}, year = {2009}, abstract = {We present a novel unimorph deformable mirror with a diameter of only 10 mm that will be used in adaptive resonators of high power solid state lasers. The relationship between applied voltage and deformation of a unimorph mirror depends on the piezoelectric material properties, layer thicknesses, boundary conditions, and the electrode pattern. An analytical equation for the deflection of the piezoelectric unimorph structure is derived, based on the electro-elastic and thin plate theory. The validity of the proposed analytical model has been proven by numerical finite-element modelling and experimental results. Our mirror design has been optimized to obtain the highest possible stroke and a high resonance frequency.}, language = {en} } @inproceedings{VerpoortRauschWittrock2012, author = {Verpoort, Sven and Rausch, Peter and Wittrock, Ulrich}, title = {Novel unimorph deformable mirror for space applications}, series = {International Conference on Space Optics (ICSO), Proc. SPIE}, volume = {10564}, booktitle = {International Conference on Space Optics (ICSO), Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-651}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6516}, pages = {1056414-1}, year = {2012}, abstract = {We have developed a new type of unimorph deformable mirror, designed to correct for low-order Zernike modes. The mirror has a clear optical aperture of 50 mm combined with large peak-to-valley Zernike amplitudes of up to 35 μm. Newly developed fabrication processes allow the use of prefabricated super-polished and coated glass substrates. The mirror's unique features suggest the use in several stronomical applications like the precompensation of atmospheric aberrations seen by laser beacons and the use in woofer-tweeter systems. Additionally, the design enables an efficient correction of the inevitable wavefront error imposed by the floppy structure of primary mirrors in future large space-based telescopes. We have modeled the mirror by using analytical as well as finite element models. We will present design, key features and manufacturing steps of the deformable mirror.}, language = {en} }