A novel criterion for evaluating the beam quality of high energy laser

Abstract

In this paper, a novel criterion for evaluating the beam quality of high energy laser is proposed, which is called “power outside the large bucket”, P OLB for short. The novel criterion does not demonstrate the divergence of the beam but focuses on the high spatial frequency wavefront aberration of the beam. The P OLB values of the laser beams with various aberrations are calculated. It shows that the more high spatial frequency components in the aberration the larger P OLB value is. Moreover, it is theoretically analyzed that the laser beams with various aberrations are corrected by ideal adaptive optics (AO) systems with different deformation mirror (DM) actuator numbers. It is shown that the residual error of the corrected wavefront aberration with many high spatial frequency components is quite large. Finally, the dependence of the residual wavefront error on the P OLB value is investigated. Only if the P OLB is smaller than 3.8/3.4/2.5/1.7 the residual error of the wavefront may be smaller than λ/10, which is corrected by an ideal AO system with 127/61/37/19 actuators. It is necessary to employ a complicated AO system for improving the laser beam of which the P OLB value is large. The novel evaluating criterion P OLB is able to demonstrate the amount of high spatial frequency aberration and the residual wavefront error corrected by AO system. It is an accessible and useful criterion for evaluating the beam quality of high energy lasers.