When adaptive optics is applied to target imaging, laser atmospheric transmission, etc., variable extension target wavefront detection is a technical challenge. And its detection accuracy directly affects the correction effect of adaptive optics.In order to explore the wavefront detection accuracy problem of variable extension targets. In this paper, a simulation model for wavefront detection of variable extension targets with correlated Hartmann was developed. The model was based on the commonly used optical system parameters, and it was also established by using the theories of Fresnel diffraction, Newton's imaging equation, the working principle of Shack-Hartmann wavefront detector, and wavefront recovery.We analyzed the effects of target distance and attitude variations on wavefront detection accuracy. The relationship curves between RMS and PV of wavefront recovered residuals and target distance and different attitudes were obtained in the simulation. And we further carried out the analysis for the intrinsic physical reasons of forming this relationship. The results show that target distance and attitude changes affected the extension of targets within the Hartmann subaperture. When the wavefront was recovered using the correlation algorithm, we obtained that the smaller the extension, the higher the wavefront detection accuracy within the relevant Hartmann detection accuracy. Therefore, it could be summarized that the smaller the extension of the target, the more similar it was to the point target, then the detection error introduced by the extension became smaller.
The uniformity of illumination can affect the detection ability of the Shack-Hartmann wavefront sensor to a certain extent and degrade the wavefront restoration accuracy. When the intensity distribution of the incident beam is very non-uniform, it is difficult for each sub-spot image to carry out optimal signal-to-noise ratio (SNR) at the same time. The spot image may be over-exposed or too dark, and that brings about the incorrect measurements of the centroid and further influences the reconstruction accuracy of the wavefront. In the paper, we use multi-frame image information fusion to generate an enhanced spot-array image with a high dynamic range, so as to improve the accuracy of the overall centroid calculation. The simulation results show that this method is effective in the above cases.
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