Characterization of the laser beam distortion due to the thermal load on high average power femtosecond laser systems

We report observation of laser beam distortion due to the thermal load associated with high energy (110 mJ) and high average power (11 Watts) femtosecond laser system with vacuum compressor. To improve laser-based light source brightness, it is crucial to develop laser systems with higher energy and higher average power. Managing the high thermal loading on vacuum optical components and demonstration of brightness stability are key issues in the implementation of this approach. We characterize such thermally induced distortions using beam wavefront measurements and propose compensation methods to attain long term stability.