Research On The Improved Optimized Algorithm Of Beam Steering For Incoherent Beam Combining

Laser has been applied to almost all fields of nature science,like physics,chemistry,biology and real applications like industry,national defense since it first came out in 1960.During the process of applications,the output power and laser beam quality are the important aspects of laser.Nevertheless,the beam quality would decrease as the output power increases limited to the influences of a series of nonlinear effects.The beam combining technology is one of the most promising methods for solving this contradiction.The technology of beam steering is the key technology in the beam combining.Additionally,the beam steering technology can be also applied to astronomical observations,modern precise guidance,free space laser communication as well as aerial imaging.Therefore,researching and developing the technology of beam steering has significant meaning and it's the necessary path to achieve high power laser beam combining.In this paper,research was carried out on the improved optimized algorithm for the technology of beam steering in incoherent beam combining.A series of critical issues were studied deeply including the issue of laser beam propagation in atmospheric turbulence and the modifications of algorithms for beam control.The effects that have big impact on the incoherent beam combining which were brought by the atmospheric turbulence like mean filed,beam expand and beam wander were studied in detail.Simulations of the incoherent beam combining system were carried out.The feasibility of the conventional algorithm and the improved algorithms were testified through simulations.The results show that the improved algorithms can be applied to the beam combining system.Experiments were set up for incoherent beam combining.The improved algorithms were testified through experiments.The contents of this paper are specified as follows:Firstly,the research status of all kinds beam combining technologies in domestic and foreign were discussed in detail.The pros and cons of every beam combining technology were analyzed.Based on the discussion,the incoherent beam combining was adopted as the primary research aspect.Besides,the architecture of the beam combining system was settled.Then the algorithms that commonly used in the field of optics were analyzed and discussed in detail.In order to guarantee the bandwidth of the system,the stochastic parallel gradient descent algorithm was adopted as the control algorithm of the beam steering.Then the convergence speed and precision of the SPGD algorithm were analyzed in detail.The model of laser beam propagation through turbulence was established.The theory of power spectrum was used to deduce the formulas of laser beam propagation under the circumstance of Kolmogorov turbulence and non-Kolmogorov turbulence.All of the theories have lay the foundation of the realization of the beam combining system.The mathematical model of the beam combining system is proposed.The feasibility of the architecture and the algorithm are testified through simulations.Some shortcomings that the algorithm encounters are modified and improved.Given the local extremum that the correction process often stuck when the parameter of the algorithm is not proper,the method that combines the pattern recognition and SPGD algorithm is proposed.The improved method can detect the local extremum efficiently and get out of the local extremum.The adaptive merit function was proposed in order to improve the entire correction process and ease the problem of radius chosen of the power in the bucket merit.The results of simulation prove that the method can ease the problem of choosing of the radius of the cost function.The momentum method is proposed and testified in this paper.The results of simulations confirm that the momentum SPGD algorithm can enhance the convergence speed of the correction process and keep the correction process steady.The experimental setup of the beam combining system is build.The fast steering mirror is used as the component of beam steering.The improved algorithm proposed in the last chapter is applied to the beam combining system.The experimental results indicate that the improved algorithm is proper for the beam steering in the beam combining system.Eventually,the summary is made for this paper,the prospect of the technology of laser beam combining and the optimization algorithm is made.