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Research on polarization Hartmann wavefront detection technology
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Abstract
Aiming at the problems of low signal-to-background ratio and low wavefront detection accuracy of the adaptive optical system Hartmann sensor under strong background conditions during the day, based on the difference in polarization characteristics between man-made targets and strong backgrounds, a polarized Hartmann wavefront detection technology is proposed. The traditional Hartmann wavefront detection is converted from the intensity dimension to the polarization dimension, thereby effectively improving the signal-to-background ratio and wavefront detection accuracy. The basic methods and principles of polarized Hartmann wavefront detection are described, and the correctness and accuracy of the method are verified through numerical simulations and experiments. Theoretical and numerical simulation results show that the polarized Hartmann wavefront detection technology can effectively improve the signal-to-background ratio and wavefront detection accuracy under strong background conditions, and significantly enhance the ability of the adaptive optical system to work under strong background conditions. -
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References
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Overview
Overview: After more than 40 years of continuous development, adaptive optics has gradually matured in theoretical exploration and engineering applications, and has been widely used in various fields. The Hartmann wavefront sensor is an important part of the adaptive optics system and is currently the most widely used wavefront detector in the adaptive optics system. When the Hartmann wavefront sensor performs wavefront detection in strong background occasions like daytime, the interference of the strong background will increase the centroid calculation error in the wavefront calculation and significantly reduce the wavefront detection accuracy, which severely limits working hours of the adaptive optics system.
Aiming at the application scenario of a large back-to-signal ratio, a new polarized Hartmann wavefront detection technology is proposed. The polarized Hartmann wavefront detector adds a polarization modulator in front of the microlens array to obtain intensity detection images under different polarization modulation states. The polarized difference principle is used to convert the directly detected intensity signal into a polarization signal, and finally, the Hartmann wavefront detection result is transformed from the intensity dimension to the polarization dimension by using the difference between the polarization characteristics of the detection target and the background light. This article describes the basic methods and principles of polarized Hartmann wavefront detection technology, and then conducts numerical simulations for linear polarization signal wavefront detection in natural light scenes, which are as follows. First, the wavefront restoration results before and after adding the strong background are compared to clarify the influence of the strong background on the Hartmann wavefront restoration results. Then, the strong background processing and wavefront restoration calculation under different back signal ratios are launched. Finally, the removal effect of the strong background and the wavefront restoration error of the subtracted global threshold method, subtracted local adaptive threshold method, and polarization difference method is compared.
Theoretical and simulation results show that the polarized Hartmann wavefront detection technology has a good removal effect on strong background, and has high wavefront restoration accuracy. This improves the signal-to-background ratio of Hartmann wavefront detection to a certain extent, and improves the accuracy of wavefront detection under strong background conditions. Therefore, the polarization Hartmann wavefront detection technology has high feasibility for wavefront detection in strong background scenes, and has a great effect on the application expansion of adaptive optics in daytime scenes.
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Figure 1.
Schematic map of the Hartmann sensor under the strong background scene
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Figure 2.
Spot array of the Hartmann-Shack wavefront sensor.
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Figure 3.
Basic principle of the proposed polarization Hartmann wavefront sensor
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Figure 4.
Schematic map of the polarization state of mixed light.
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Figure 5.
Schematic map of polarization modulation of the polarization Hartmann sensor
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Figure 6.
Reference signal sub-aperture spot image and its restored wavefront and Zernike coefficient.
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Figure 7.
Mixed signal sub-aperture spot image and its wavefront restoration image and wavefront Zernike coefficients.
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Figure 8.
Sub-aperture spot image processed by various methods for strong background.
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Figure 9.
The restored wavefront image and its Zernike coefficient expression after three processing methods.
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Figure 10.
Wavefront restoration error using different methods.
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Figure 11.
RMS value curve of wavefront restoration error for different RBS.
