Research On Adaptive Optics Hartmann Spot Centroid Detection Technology

Adaptive optics technology originated from the demand of astronomical research.It can detect and compensate wave-front phase distortion in real time,and it has been widely used in laser atmospheric transmission,optical measurement,and medicine.Compared with other wave-front detection devices,the Shack-Hartmann wave-front sensor has been widely used due to its advantages such as high light energy utilization,simple structure,and large dynamic range of measurement.Its working principle is based on the deviation of the centroid of the spot.The displacement is used to reconstruct the distorted wave-front,so the detection accuracy of the spot center of the Hartmann array directly affects the wave-front reconstruction accuracy.In this paper,a series of researches are carried out from the aspects of wave-front beacon extraction and slope calculation.This paper analyzes the related principle of Hartmann wave-front sensor,the characteristics of the adaptive optical point source beacon spot image,the noise in the system,and requirements of the system for the Hartmann wave-front image processing algorithm.According to the characteristics of the spot image and the noise characteristics,a new method of measuring the spot centroid based on the adaptive threshold is proposed.Aiming at the bulk shot noise in the system,a median filtering method is adopted.The residual noise is cut off by the adaptive threshold segmentation method.Then from the perspective of the morphological connectivity of the image,the spot image is located and validated.Finally,the centroid calculation window is constructed and the centroid calculation is performed.This algorithm combines several aspects such as the positioning of the spot area,spot validity validation,adaptive threshold segmentation,and the construction of the centroid detection window.The process of each step of the algorithm is analyzed and discussed in detail.The analysis of the relevant parameters in the algorithm is performed in detail to determine the value or range of those parameters.A series of simulation experiments are conducted to verify the accuracy and stability of the proposed algorithm.And comparisons of simulation results between the proposed new algorithm,the commonly used mean background algorithm,the optimum threshold algorithm and the percentage threshold algorithm are performed and analyzed.The correlation results show that the calculated centroid error,mean square error and PV value of the proposed algorithm are all less than the other three algorithms.Four algorithms are used to process the Hartmann array spot images collected in practical experiments.The results are compared and analyzed.The experimental results show that the algorithm proposed in this paper has good stability and repeatability.