@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}
}
@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{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}
}
@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}
}
@article{VerpoortWittrock2010,
  author    = {Verpoort, Sven and Wittrock, Ulrich},
  title     = {Actuator patterns for unimorph and bimorph deformable mirrors},
  series = {Appl. Opt.},
  volume    = {49},
  journal   = {Appl. Opt.},
  publisher = {OSA},
  doi       = {10.25974/fhms-649},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6490},
  pages     = {G37 -- G46},
  year      = {2010},
  abstract  = {The actuator pattern of an adaptive mirror determines the amplitudes and the fidelities of the mirror deformations that can be achieved. In this study, we analyze and compare different electrode patterns of piezoelectric unimorph deformable mirrors using a numerical finite element model. The analysis allows us to determine the optimum actuator pattern, and it is also applicable to bimorph mirrors. The model is verified by comparing its predictions with experimental results of our prototype of a novel unimorph deformable mirror.},
  language  = {de}
}
@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}
}
@article{Vennemann2014,
  author    = {Vennemann, Peter},
  title     = {Zukunft der Stromspeicherung in Pumpspeicherkraftwerken},
  series = {Deutsches Ingenieurs-Blatt},
  volume    = {2014},
  journal   = {Deutsches Ingenieurs-Blatt},
  number    = {3},
  doi       = {10.25974/fhms-695},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6954},
  year      = {2014},
  abstract  = {Mit wenigen Ausnahmen wird im elektrischen Versorgungssystem die Pumpspeichertechnik zur Pufferung gr{\"o}ßerer Abweichungen zwischen momentanem Stromverbrauch und -erzeugung und zur zeitlichen Verschiebung von Lasten eingesetzt. Erste großtechnische Anlagen wurden bereits Ende der zwanziger Jahre des letzten Jahrhunderts in Deutschland gebaut, um die Auslastung thermischer Kraftwerke gleichm{\"a}ßiger zu erm{\"o}glichen. Pumpspeicherwerke bieten sich somit als Referenztechnologie an, mit der sich neue Entwicklungen messen m{\"u}ssen. Ein {\"U}berblick.},
  subject      = {Energiewirtschaft},
  language  = {de}
}
@misc{Schultealbert2011,
  type      = {Master Thesis},
  author    = {Schultealbert, Susanne},
  title     = {Wasser- und Sanit{\"a}rversorgung von Schulen und Gesundheitsstationen f{\"u}r exemplarische F{\"a}lle im l{\"a}ndlichen Raum {\"A}thiopiens},
  publisher = {FH M{\"u}nster},
  doi       = {10.25974/fhms-484},
  url       = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-4843},
  school      = {FH M{\"u}nster - University of Applied Sciences},
  year      = {2011},
  abstract  = {Eine besonders von Wassermangel betroffene Region ist das Bundesland Afar im Nordosten {\"A}thiopiens. In diesem Gebiet befindet sich das Dorf Hidmo. Mittels Geldern aus der Entwicklungshilfe hat die {\"a}thiopische Regierung dort ein Schulgeb{\"a}ude errichten lassen, damit die Kinder aus der Umgebung der allgemeinen Schulpflicht nachkommen k{\"o}nnen. Es wurde aber vergessen, Geld f{\"u}r eine Wasser-und Sanit{\"a}rversorgung einzuplanen, diese w{\"a}re notwendig, da die n{\"a}chste Wasserstelle 500 m weit entfernt ist. Im Rahmen dieser Arbeit soll auf Vorplanungsniveau untersucht werden, inwiefern es m{\"o}glich ist, Niederschlagswasser zu speichern, welches den Sch{\"u}lern als Wasserquelle dient und welche Sanit{\"a}rsysteme daf{\"u}r in Frage kommen. Zum einen sollen diese das Ausbreiten von Krankheiten verhindern und zum anderen die knappe Ressource Wasser schonen. Zus{\"a}tzlich soll versucht werden, Bew{\"a}sserungswasser bereit zu stellen, zur Bew{\"a}sserung eines schuleigenen Nutzgartens, der dazu dienen soll, die Kinder in sparsamen Bew{\"a}sserungsmethoden zu schulen. Der Wasserspeicher soll nur Brauchwasser zum H{\"a}ndewaschen und zu Bew{\"a}sserungszwecken liefern. Trinkwasser soll mittels einer Rohrleitung aus der vorhandenen, 500m von der Schule entfernten, Wasserquelle bezogen werden. Zur Auswahl sollen nur angepasste Technologien kommen, vorwiegend einfach gehalten, dem Prinzip der Kreislaufwirtschaft nahekommend.},
  subject      = {Trinkwasserversorgung},
  language  = {de}
}