@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{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} } @inproceedings{RauschVerpoortWittrock2016, author = {Rausch, Peter and Verpoort, Sven and Wittrock, Ulrich}, title = {Unimorph piezoelectric deformable mirrors for space telescopes}, series = {Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, Proc. SPIE}, volume = {9904}, booktitle = {Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, Proc. SPIE}, doi = {10.25974/fhms-923}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-9230}, pages = {990468}, year = {2016}, abstract = {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.}, language = {de} } @inproceedings{SauvageAmiauxAustinetal.2016, author = {Sauvage, Marc and Amiaux, J{\´e}rome and Austin, James and Bello, Mara and Bianucci, Giovanni and Chesn{\´e}, Simon and Citterio, Oberto and Collette, Christophe and Correia, S{\´e}bastien and Durand, Gilles A. and Molinari, Sergio and Pareschi, Giovanni and Penfornis, Yann and Sironi, Giorgia and Valsecchi, Guiseppe and Verpoort, Sven and Wittrock, Ulrich}, title = {A development roadmap for critical technologies needed for TALC: a deployable 20m annular space telescope}, series = {Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, Proc. SPIE}, volume = {9904}, booktitle = {Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, Proc. SPIE}, doi = {10.25974/fhms-924}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-9248}, pages = {99041L}, year = {2016}, abstract = {Astronomy is driven by the quest for higher sensitivity and improved angular resolution in order to detect fainter or smaller objects. The far-infrared to submillimeter domain is a unique probe of the cold and obscured Universe, harboring for instance the precious signatures of key elements such as water. Space observations are mandatory given the blocking effect of our atmosphere. However the methods we have relied on so far to develop increasingly larger telescopes are now reaching a hard limit, with the JWST illustrating this in more than one way (e.g. it will be launched by one of the most powerful rocket, it requires the largest existing facility on Earth to be qualified). With the Thinned Aperture Light Collector (TALC) project, a concept of a deployable 20 m annular telescope, we propose to break out of this deadlock by developing novel technologies for space telescopes, which are disruptive in three aspects: \&\#8226; An innovative deployable mirror whose topology, based on stacking rather than folding, leads to an optimum ratio of collecting area over volume, and creates a telescope with an eight times larger collecting area and three times higher angular resolution compared to JWST from the same pre-deployed volume; \&\#8226; An ultra-light weight segmented primary mirror, based on electrodeposited Nickel, Composite and Honeycomb stacks, built with a replica process to control costs and mitigate the industrial risks; \&\#8226; An active optics control layer based on piezo-electric layers incorporated into the mirror rear shell allowing control of the shape by internal stress rather than by reaction on a structure. We present in this paper the roadmap we have built to bring these three disruptive technologies to technology readiness level 3. We will achieve this goal through design and realization of representative elements: segments of mirrors for optical quality verification, active optics implemented on representative mirror stacks to characterize the shape correction capabilities, and mechanical models for validation of the deployment concept. Accompanying these developments, a strong system activity will ensure that the ultimate goal of having an integrated system can be met, especially in terms of (a) scalability toward a larger structure, and (b) verification philosophy.}, 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{VorholtWittrock2015, author = {Vorholt, Christian and Wittrock, Ulrich}, title = {Intra-cavity pumped Yb:YAG thin-disk laser with 1.74\% quantum defect}, series = {Opt. Lett.}, volume = {40}, journal = {Opt. Lett.}, doi = {10.25974/fhms-828}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8284}, pages = {4819 -- 4822}, year = {2015}, abstract = {We present, to the best of our knowledge, the first intracavity pumped Yb:YAG thin-disk laser. It operates at 1050.7 nm with a quantum defect of just 1.74\% due to pumping at 1032.4 nm. Low absorption of the pump light at the pump wavelength of 1032.4 nm is compensated for by placing the disk inside the resonator of another Yb:YAG thin-disk laser which is diode-pumped at 940 nm. The intra-cavity pumped laser has an output power of 10.3 W and a slope efficiency of 8.3\%}, language = {en} } @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} } @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{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} } @article{Wittrock2014, author = {Wittrock, Ulrich}, title = {Grenzen? Welche Grenzen? Prof. Ulrich Wittrock, Leiter des Labors f{\"u}r Photonik an der Fachhochschule M{\"u}nster, fragt nach den ultimativen Grenzen der Lasertechnik}, series = {Laser Community - das Lasermagazin von Trumpf}, volume = {02:14}, journal = {Laser Community - das Lasermagazin von Trumpf}, year = {2014}, language = {de} }