Optimization of ultrashort pulse written volume-Bragg-gratings in fused silica for high power applications (Conference Presentation)

The ongoing increase of peak and average power of diode lasers makes the consideration of thermo-optical effects due to absorption in the optical system necessary. Otherwise, this local increase in temperature might lead to a significant reduction of the entire functionality or a complete failure. Here, we consider this issue in volume Bragg gratings (VBG) as they are typically used for wavelength stabilization of the laser diodes. Conventionally, these gratings are fabricated very effectively by inscription using ultraviolet light into special photosensitive glasses. However, the use of these special glasses might compromise the transmission and, thus, limit the application. As an alternative, we inscribe VBGs in pure fused silica using ultrashort laser pulses and the phase mask scanning technique. Applying these gratings for external stabilization of high power diode lasers already demonstrated an outstanding performance in sense of spectral drift due to load change compared to conventional VBGs. Here, we present investigations to further optimize the residual absorption of the gratings especially in the NIR. Apart from analyzing the influence of the processing parameters on the residual absorption, we also studied the possibility for a thermal post-processing to anneal absorbing defects. The resulting gratings exhibit a residual absorption close to the intrinsic absorption of fused silica, making them ideally suited for high power applications. Further applications in ultrashort pulse laser systems for pulse stretching and compression are discussed.