TY - CHAP A1 - Wittrock, Ulrich A1 - Welp, Petra T1 - Adaptive laser resonator control with deformable MOEMS mirrors T2 - MEMS/MOEMS Components and Their Applications III, Proc. SPIE N2 - 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. Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-6537 VL - 6113 SP - 61130C PB - SPIE ER - TY - CHAP A1 - Wilming, Heinrich A1 - Riedl, Alexander T1 - TA Luft - Chance zur regelwerksübergreifenden Standardisierung dichter Flanschverbindungen T2 - XXI. Dichtungskolloquium Y1 - 2019 SP - 41 EP - 48 PB - FH Münster CY - Münster ER - TY - CHAP A1 - Wang, Hao A1 - Gurevich, Evgeny L A1 - Ostendorf, Andreas T1 - Microhardness and microabrasion behaviour of NiTi shape memory alloy after femtosecond laser shock peening without coating in air T2 - High-Power Laser Materials Processing: Applications, Diagnostics, and Systems IX N2 - The experiment study presents the influence of femtosecond laser shock peening (FsLSP) without a protective layer in the air on the surface hardness and surface mechanical property of NiTi shape memory alloy. Femtosecond laser shock peening is a new possibility of direct laser ablation without any protective layer under atmospheric conditions, which can produce intense shock waves with low pulse energy in the air. The average surface roughness values of the NiTi alloy samples were measured, because the surface roughness may affect its friction resistance. The results showed that the surface roughness of NiTi increased after femtosecond laser shock peening treatment. In comparison with the initial state, the coefficient of friction decreased and surface microhardness increased after femtosecond laser shock peening treatment with different FsLSP parameters. This improvement of wear properties may be attributed to the enhancement of surface microhardness and surface titanium oxide layer induced by the shock wave and laser ablation during FsLSP treatment. Y1 - 2020 U6 - http://dx.doi.org/10.1117/12.2543550 SP - 1127301 EP - 1127301 PB - International Society for Optics and Photonics CY - USA ER - TY - CHAP A1 - Wang, Hao A1 - Gurevich, Evgeny L A1 - Ostendorf, Andreas T1 - Application of nanoindentation technique to test surface hardness and residual stress of NiTi alloy after femtosecond laser shock peening T2 - High-Power Laser Materials Processing: Applications, Diagnostics, and Systems X / SPIE.Digital.Library N2 - Laser shock peening is a new and important surface treatment technique that can enhance the mechanical properties of metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. The femtosecond laser shock peening in the air has been studied recently, which can induce higher pressure shock wave than that of traditional nanosecond laser shock peening in a very short time. The NiTi alloy is processed by femtosecond laser shock peening, then a nanoindentation device is used to measure its surface hardness and residual stress. The hardness results of NiTi alloy before and after treatment show that the femtosecond laser shock peening can increase the hardness of NiTi alloy, which also shows that the femtosecond laser can be used to perform laser shock peening on NiTi alloy without coating. Y1 - 2021 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11679/116790J/Application-of-nanoindentation-technique-to-test-surface-hardness-and-residual/10.1117/12.2593092.full?tab=ArticleLinkReference U6 - http://dx.doi.org/10.1117/12.2593092 SP - 116790J-0 EP - 116790J-5 PB - International Society for Optics and Photonics CY - USA ER - TY - CHAP A1 - Vorholt, Christian A1 - Wittrock, Ulrich T1 - Wavelength control by angle-tuning of the laser radiation in an intra-cavity pumped Yb:YAG thin-disk laser T2 - Advanced Solid State Lasers (ASSL), paper AM5A.39 N2 - 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. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-8298 UR - https://www.osapublishing.org/abstract.cfm?uri=ASSL-2015-AM5A.39 ER - TY - CHAP A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Deformable mirrors for high power lasers T2 - Proceedings of the 8th International Workshop on Adaptive Optics for Industry and Medicine (AOIM) N2 - 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. KW - Deformable mirror, adaptive mirror, unimorph mirror, high-power laser Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-106953 UR - http://congresos.um.es/aoim/aoim2011/schedConf/presentations ER - TY - CHAP A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Novel unimorph deformable mirror with monolithic tip-tilt functionality for solid state lasers T2 - MEMS Adaptive Optics V, Proc. SPIE N2 - 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. Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-6471 VL - 7931 SP - 793107 PB - SPIE ER - TY - CHAP A1 - Verpoort, Sven A1 - Wittrock, Ulrich T1 - Unimorph deformable mirror for telescopes and laser applications in space T2 - International Conference on Space Optics (ICSO), Rhodes Island, Greece N2 - 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 Maréchal criterion. Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-6484 UR - www.icsoproceedings.org PB - SPIE ER - TY - CHAP A1 - Verpoort, Sven A1 - Welp, Petra A1 - Wittrock, Ulrich T1 - Novel unimorph deformable mirror for solid state laser resonators T2 - MEMS Adaptive Optics III, Proc. SPIE N2 - 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. Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-6504 VL - 72090N PB - SPIE ER - TY - CHAP A1 - Verpoort, Sven A1 - Rausch, Peter A1 - Wittrock, Ulrich T1 - Novel unimorph deformable mirror for space applications T2 - International Conference on Space Optics (ICSO), Proc. SPIE N2 - 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. Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:hbz:836-opus-6516 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10564/1056414/Novel-unimorph-deformable-mirror-for-space-applications/10.1117/12.2309089.full VL - 10564 SP - 1056414-1 PB - SPIE ER -