Phasenkonjugation. Grundlagen fuer die Phasenkonjugation durch stimulierte Streuprozesse Abschlussbericht

With increasing pump power there are thermally induced aberrations in solid state lasers, having direct consequences for the beam quality and efficiency of the laser. Therefore the aim of the project was to carry out preparatory research for compensating aberrations by means of phase conjugation through stimulated Brillouin-scattering, and adaptive optics. In order to determine the most favourable parameters for this kind of phase conjugation there were carried out investigations, which showed the effect of laser output energy, pulse behaviour, pulse duration, beam quality and coherence length on the efficiency and quality of the phase conjugation process. An optimally designed system resulted in a threshold energy of about 4 mJ and a reflection coefficient up to 40% at 8 - 10 mJ laser energy. As adaptive optical elements a deformable mirror on the one hand and a liquid crystal cell with spatial resolved, variable phase shift on the other hand was investigated. The deformable mirror is assembled with one actuator and allows radii of curvature from 1 m to infinity, allowing to compensate the focal part of the thermal lens. The attained prototype however shows relatively high portions of astigmatism and coma. Further there were carried out investigations on liquid crystal cells with structured electrodes (68 #mu#m width, 1.5 #mu#m distance). These cells were used as phase shifting elements (#approx# 7 #pi#) at wavelengths of 632 and 1064 nm. Only very little diffraction appeared as a result of the discrete electrode structure. Contrary to the stimulated Brillouin-scattering, which is a threshold process, the both adaptive methods are also applicable for lasers in the lower and medium power range, that means also for continuous wave lasers. (orig.)SIGLEAvailable from TIB Hannover: F94B1498+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman