Bootstrap Beacon Creation for Dynamic Wavefront Compensation

摘要

The task of delivering sufficient level of airborne laser energy to ground based targets is of high interest. To overcome the degradation in beam quality induced by atmospheric turbulence, it is necessary to measure and compensate for the phase distortions in the wavefront. Since, in general, there will not be a cooperative beacon present, an artificial laser beacon is used for this purpose. In many cases of practical interest, beacons created by scattering light from a surface in the scene are anisoplanatic, and as a result provide poor beam compensation results when conventional adaptive optics systems are used. In this paper we present three approaches for beacon creation in a down-looking scenario. In the first approach we probe whole volume of the atmosphere between transmitter and the target. In this case the beacon is created by scattering an initially focused beam from the surface of the target. The second approach describes generation of an uncompensated Rayleigh beacon at some intermediate distance between the transmitter and the target. This method allows compensation for only part of the atmospheric path, which in some cases provides sufficient performance. Lastly, we present a novel technique of "bootstrap" beacon generation that allows achieving dynamic wavefront compensation. In this approach a series of compensated beacons is created along the optical path, with the goal of providing a physically smaller beacon at the target plane. The performance of these techniques is evaluated by using the average Strehl ratio and the radially averaged intensity of the beam falling on the target plane. Simulation results show that under most turbulence conditions of practical interest the novel "bootstrap" technique provides better power in the bucket in comparison with the other two techniques.