High-quality spatial modes for petawatt-class lasers

In this paper, we report the methods used to obtain laser pulses with high spatial quality at the Berkeley Laboratory Laser Accelerator (BELLA) facility are reported. Strehl ratios of 0.85 have been achieved using a closed-loop adaptive optics system consisting of a deformable mirror and wavefront sensors. The implementation and the optimization techniques are described. Additionally, the challenges associated with running a deformable mirror on a petawatt-class laser are addressed. In addition to mitigating aberrations introduced by various optical components of the system, aberrations induced by different laser powers can also be compensated for. This allows for tunable laser powers without the need for cryogenic cooling of the final amplifiers.