@inproceedings{VorholtWittrock2015, author = {Vorholt, Christian and Wittrock, Ulrich}, title = {Wavelength control by angle-tuning of the laser radiation in an intra-cavity pumped Yb:YAG thin-disk laser}, series = {Advanced Solid State Lasers (ASSL), paper AM5A.39}, booktitle = {Advanced Solid State Lasers (ASSL), paper AM5A.39}, doi = {10.25974/fhms-829}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8298}, year = {2015}, abstract = {In an intra-cavity pumped thin-disk laser the pump radiation forms a standing wave pattern inside the intra-cavity pumped disk.We demonstrate experimentally that the grating period of the standing wave pattern of the pump radiation can control the laser wavelength.}, 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{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} } @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} } @inproceedings{DurandAmiauxSauvageetal.2016, author = {Durand, G. and Amiaux, J. and Sauvage, M. and Austin, J. and Chesne, S. and Collette, C. and Helgouashl, S. and Pareschi, J. and Penfornis, Y. and Valsecchi, G. and Wittrock, U.}, title = {TALC a far-infrared 20m space telescope and the ELICSIR consortium to reach TRL 3}, series = {Proceedings of the 37th ESA Antenna Workshop, Noordwijk, Netherlands}, booktitle = {Proceedings of the 37th ESA Antenna Workshop, Noordwijk, Netherlands}, doi = {10.25974/fhms-925}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-9253}, year = {2016}, abstract = {Further space exploration in the far-infrared (FIR) requires larger apertures in order to improve the spatial resolution of captured images. To this purpose, the Thinned Aperture Light Collector (TALC) concept of a deployable annular telescope has been recently developed at CEA, which offers novel perspectives for FIR space missions. The consortium ELICSIR consortium of European institutes and companies has been created to improve the technological readiness level (TRL) of its key systems and components.}, language = {en} } @article{WittrockVorholt2015, author = {Wittrock, Ulrich and Vorholt, Christian}, title = {Spatial hole burning in Yb:YAG thin-disk lasers}, series = {Appl. Phys. B}, volume = {120}, journal = {Appl. Phys. B}, doi = {10.25974/fhms-823}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8234}, pages = {711 -- 721}, year = {2015}, abstract = {The spatially varying intensity in a standing wave resonator leads to spatial hole burning in the gain medium of a laser. The spatial hole burning changes the gain of different longitudinal modes and can thus determine the optical spectrum of the laser. We simulate this longitudinal mode competition in standing wave resonators of thin-disk lasers. The resulting optical spectra of the laser are compared to measured optical spectra. We examine two types of resonators: I-resonators and V-resonators with different angles of incidence. In V-resonators, the non-normal incidence of the laser beam on the disk lifts the degeneracy of the polarization. Experiments show that the slight gain advantage for the p-polarization does not lead to polarized emission. For both types of resonators, the measured spectra are in good agreement with the simulated ones. The simulations allow to study the influence of spectral intra-cavity losses on the optical spectrum of a thin-disk laser.}, 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} } @article{VorholtWittrock2017, author = {Vorholt, Christian and Wittrock, Ulrich}, title = {Single-frequency oscillation of thin-disk lasers due to phase-matched pumping}, series = {Opt. Expr.}, volume = {25}, journal = {Opt. Expr.}, doi = {10.25974/fhms-1025}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-10258}, pages = {21388 -- 21399}, year = {2017}, abstract = {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.}, 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{PerchermeierWittrock2013, author = {Perchermeier, Julian and Wittrock, Ulrich}, title = {Precise measurements of the thermo-optical aberrations of an Yb:YAG thin-disk laser}, series = {Opt. Lett.}, volume = {38}, journal = {Opt. Lett.}, publisher = {OSA}, doi = {10.25974/fhms-685}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6854}, pages = {2422 -- 2424}, year = {2013}, abstract = {We report on interferometric measurements of the thermo-optical aberrations of the laser medium of an Yb:YAG thin-disk laser in pumped and cw lasing conditions at several pump-power levels with a mean repeatability of 5 nm. These measurements build the basis for future intracavity compensation of the aberrations with our deformable mirror in order to improve the fundamental-mode efficiency.}, language = {en} }