Nonlinear Optical Frequency Conversion for Lasers in Space

Kurzfassung

A frequency conversion unit, based on two BiBO crystals in a crystal holder suitable for a future space mission, is presented within this work. Conversion efficiency at second harmonic generation followed by sum frequency generation was realized to be as high as 48±2 %, converting the fundamental radiation in the infrared at a wavelength of 1064 nm to a radiation in the ultraviolet at a wavelength of 355 nm. The realized conversion efficiency overcomes studies conducted in the past and fulfills the requirements as stated by the European Space Agency. Further on, the conducted experiments like laser calorimetry and detection of wavefront deformations during frequency conversion, as well as a longterm experiment, revealed the excellent optical properties of the BiBO crystals. A potential drawback of BiBO crystals could be the lower damage threshold when compared to LBO crystals and further research needs to be conducted on this topic. In KTP crystals, highly efficient generation of second harmonic radiation at a wavelength of 532 nm and a conversion efficiency of 76±3 % was demonstrated. A method to detect gray-tracking in situ is presented within this thesis and the formation of color centers during longterm operation is observed. It is revealed that the gray-tracking could be a limiting factor for a spaceborne application due to the change in absorption and the resulting changes in thermal lensing.