Research On Adaptive Optics Beam Cleanup Based On Correlation Algorithms

Beam cleanup is an important application of adaptive optics.The wavefront distortion of the laser beam is detected by the wavefront detector in real time.The wavefront aberration is compensated by the wavefront corrector to compensate the beam aberration and improve the beam quality.The Shack-Hartmann wavefront sensors are widely employed in such systems.The microlens array is used to segment and sample the wavefront to recover the wavefront information.Among them,the accurate spot position is the basis of the above wavefront sensor,and its accuracy has a direct impact on the accuracy of wavefront detection.At present,the center of gravity method are the most common algorithms for spot location detections.However,for slab solid lasers,due to the poor uniformity of the beam intensity,the signal-to-noise ratio of the spots in certain sub-aperture of the Hartmann sensor are low.In addition,due to the influence of local high-order aberrations,the spot in some sub-apertures is severely deformed.The above factors will cause the calculation of the center of gravity method to be inaccurate.The correlation algorithm calculates the spot position based on template matching.Compared with the center of gravity method,the noise resistance is stronger and the robustness is better,but the time complexity and space complexity are also increased.In this dissertation,correlation algorithms are applied in solid-state laser beam cleanup.Firstly,after the simulation model is established,the influence of different correlation factors of the correlation algorithm on calculating time and accuracy are discussed.The influences of reference image category and reference image size on detection accuracy are also discussed.In order to reduce the error caused by discrete sampling,the Equiangular line interpolation method,parabolic interpolation method,Gaussian interpolation method and least square interpolation method are used to interpolate these correlation algorithms to obtain the spot position under sub-pixel precision.The above discussion provides a reference for selecting appropriate correlation algorithm parameters at different SNRs when calculation time and precisions are strictly defined.Subsequently,the contrast experiments between the absolute difference algorithm and the center of gravity method in the correlation algorithms are carried out on in experiments.It can be seen from the results that both the center of gravity method and the absolute difference algorithm can achieve good results at high SNRs.Among them,the absolute difference calculation takes longer than the center of gravity method,and the time consumption is inversely proportional to the size of the reference matrix.In order to verify the anti-noise performance of the two algorithms,the contrast experiments under different SNRs are added in this paper.The conclusions show that the absolute difference algorithm has better anti-noise performance.Finally,the beam clean up experiment was carried out on a slab solid laser.The absolute difference algorithm in the correlation algorithm is used.Experiments show that the beam quality after correction is better than the center of gravity method,which proves the feasibility of the correlation algorithms in the solid-state laser beam clean up system.