Single-pixle detector based computational ghost imaging (CGI) reconstructs an image by measuring the correlations between the scene and a series of masks. Recently, multi-pixels detector and parallel encoding is used to reduce modulation times and improve imaging speed. Due to the separate characteristics of encoding and detection in CGI system, detector defocus will not lead to image blurring in this single-pixel detector based CGI. However, detector defocus in multi-pixels detector based CGI is different to single-pixle detector based system. In this paper, based on the principle of CGI and the model of detector defocus, the influence of detector defocus in CGI is theoretically analyzed. Simulation and experiment results indicate that the multi-pixels detector based CGI inherits characteristics of antidefocus. The quality of reconstructed image is mainly affected by the degree of defocus and the array size of the detector.
In laser guidance, the response uniformity of the four quadrant photodetector has an important influence on the guidance accuracy. Each quadrant photodetector needs to measure the response consistency between quadrants and be calibrated to the same response. In this paper, large area uniform laser irradiation is used to measure the inhomogeneity between detector quadrants. The gain compensation method is used to calibrate the inhomogeneity between detector quadrants. The main core of this method is that it needs to be able to modulate the intensity of the light source; the area of the light source can be modulated, and the maximum area should be able to completely cover the four photosensitive surfaces of the detector; the light source is a beam of uniform light power. In order to solve the problem that the uniform light effect is not ideal in traditional measurement methods such as spreading beam and frosted glass scattering, a beam expander and a beam homogenizer are used to realize the high uniformity of the uniform light spot. The detector is mounted on the single axis turntable and rotated around the optical axis to make the light received on the detector more uniform. This method realizes a four-quadrant detector for consistency calibration of quadrant response in the range of optical power of a certain wavelength. The method is simple, precise, stable and easy to implement.
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