Design And Development Of Curvature Wavefront Sensing System For Mephisto

The Multi-channel Photometric Survey Telescope(Mephisto)is a telescope with a large aperture(1.6 m)and a large field of view(3.14 square degrees).Based on a consideration of image quality control and barrel design,Mephisto has adopted a fast focal ratio of 1.3 for the primary mirror,and therefore the secondary mirror has a high sensitivity to misalignments.To ensure and maintain the high-resolution imaging of Mephisto,it is necessary to calculate misalignments of the secondary mirror in real time by multiple curvature wavefront sensors in the edge FOV.In this work,we design and build the corresponding curvature wavefront sensing system according to the system characteristics of Mephisto,and the main research contents are divided into the following three parts.1.Signal source screening and optimization algorithm.Firstly,the background noise and low-intensity invalid signals are removed by the denoising process;secondly,the signal number source is flagged by the connected area tagging algorithm;and then,the SNR is used as the screening biomarker to extract the optimal signal.For the problem of overlapping related defocused images in the high-density signal source region of the sky survey area,the coupled signal is decoupled by region segmentation and curve fitting.The purpose of this algorithm is to filter out high-quality signals from the original Star source images with many signals and complex structure,so as to provide data support for wavefront reconstruction calculation.2.Wavefront reconstruction algorithm for split curvature wavefront sensor.First,the defocused images of different FOVs are corrected to eliminate the reconstruction errors caused by the inconsistent optical properties of the defocused images of different FOVs;then,the wavefront reconstruction is performed by the FFT iterative algorithm with the intensity compensation algorithm.The algorithm uses the light intensity distribution on the defocus plane to reconstruct the wavefront,and the calculation results will be used as the basis for the correction of secondary mirror misalignment.3.Curvature wavefront sensing software system.The system software is designed and developed based on the signal source screening algorithm and wavefront reconstruction algorithm.Firstly,according to the practical application requirements of curvature wavefront sensor in Mephisto,the overall software is divided into modules and functions,and then its components are realized one by one on the basis of function module division.Finally,it is verified by simulation data,and the design results are displayed.