The entire beam wavefront control of high power laser facility

Abstract

Experiment of entire beam wavefront compensation was carried out in a beamline of a high power laser facility, and two adaptive optics systems with different intentions were applied in the chosen beamline. After correction, the far-filed irradiance distribution is concentrated evidently and the entrance rate of 3ω focal spot to a 500-μm hole is improved to be about 95% under number kilojoules energy. IntroductionIn high power laser facility for Inertial Confinement Fusion (ICF) research, wavefront aberrations leading to worsen beam quality are common [1~2] . The wavefront is generally distorted in two main portions in such laser system, including the main amplifier (MA) system and the beam transfer system (BTS) to target. In MA, aberrations can originate from the pump-induced distortions, the previous-shot thermal distortions, and the mounting and coating induced optics distortions. As for BTS, several large aperture mirrors are needed to transmit the beam from MA to the target. Since most of them are inclinedly mounted which results in serious influence from gravity and mounting stress, wavefront aberrations are unavoidably induced. Generally, a smaller spot size is required for laser system. In order to meet this goal, it is not enough to limit wavefront distortions of subsystem in ICF laser facility only, and a wavefront control system is needed. Adaptive optics (AO) is considered as one of the most competitive candidates to effectively control wavefront distortions in high power laser, such as NIF (National Ignition Facility), LMJ (Laser Megajoule) and so on [3][4][5][6] . In these AO systems, the deformable mirror (DM) is mounted on cavity end, and the Hartmann-Shack wavefront sensor (WFS) is located in output sensor package (OSP). Such AO systems can compensate the aberrations in MA. Most of them ignore the control of BTS wavefront aberrations. In this paper, a novel method with two adaptive optics systems is proposed to compensate the wavefront distortions of entire laser beamline. Firstly, the arrangement of two AO systems in a newly constructed beamline in the high power solid laser facility in China is introduced. In the next section, the experiment results are presented and discussed, which demonstrate that the novel method could increase the energy concentration effectively. The laser device and wavefront control systemThe experiment is carried out in a beamline of a high power laser facility in China, which is