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978-3-8439-0906-8, Reihe Physik
Stabilized High Power Lasers and Spatial Mode Conversion
134 Seiten, Dissertation Universität Hannover (2013), Hardcover, B5
The second generation gravitational wave detectors require high laser power in order to improve the shot noise limited sensitivity. The use of high power lasers is, however, only beneficial if technical laser noise can be minimized to reduce its coupling to the detector sensitivity. The 200W laser system developed for the use in Advanced LIGO was stabilized regarding its spatial mode profile, its beam pointing and its power and frequency noise.
Along with the use of high laser powers come other effects such as thermal lensing which can possibly affect the operation of gravitational wave detectors. A measurement method was developed which allows to determine thermal lensing in commonly used optics. The measured quantity does not depend on beam parameters nor on the position of the optic under investigation. The measurements performed on EOM crystals which were used in gravitational wave detectors showed that some of the crystals could not be used in second generation detectors due to the photo-refractive effect.
In the future gravitational wave detectors noise sources will become important that were negligible in the first generation of gravitational wave detectors such as coating Brownian thermal noise. One approach to reduce this noise is the use of light in the LG33 mode in these detectors. Thus the generation of a high power helical LG33 mode with a mode purity of 95% and a power of 83W was demonstrated for the first time. This is an important step to show the feasibility of using these modes in third generation gravitational wave detectors.