High-energy Laser System Beam Quality Evaluation Study

This dissertation, firstly, summarizes some conventional appraisal criterions of laser beam quality, and then introduces the basic segments of the high energy laser beam propagation processes, the atmospheric influence on the beam quality as well as the fundamental method of beam quality measurement. Our primary research focuses on the effect of astigmation to diffraction limit multiple factor β and Strehl ratio, and a comprehensive evaluation method to AO system. The main achievements and innovative highlight in this dissertation as follows:1 Aiming at the difficulties in measuring the large aperture beam quality; it is found that the atmospheric turbulence has little influence on beam quality by analyzing the atmosphere influence on far-field quality of laser beam.2 By investigating the influence of different astigmation to diffraction limit multiple factor β and Strehl ratio, the relationships among the astigmation, β and Strehl ratio were established; which will be used for finding out the different astigmation sources of high energy laser system by measuring the ration of diffraction limit multiple factor β and Strehl ratio.3 Considering the structure of high energy laser system and the calculation method of beam quality, a new target parameter for evaluating AO system is presented. This parameter also considers the atmospheric factor and the factor of beam quality on the entrance of AO system, which is an improvement comparing old parameter that only considered atmospheric factor. At one time, using this target parameter, the far-field beam quality can be estimated when the beam quality of output laser and the coherent length of atmosphere are given. The experimental results agree with the theory very well when this method is used.In the end of this dissertation, the practical meaning and application foreground are summarized, and the disadvantages of design and the future work are also pointed out.