Research on wavefront measurement technology of space-based telescope using Shack-Hartmann wavefront sensor
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摘要
精确的测量和控制星载望远镜的波前像差是实现高效空间引力波探测的关键。本文提出了一种基于夏克-哈特曼波前传感器原理的星载望远镜波前像差测量方法,该方法采用经过频域阈值去噪处理后的频域上的互相关算法,使用子孔径数20×16、微透镜尺寸0.279 mm×0.279 mm、焦距34 mm的夏克-哈特曼波前传感器对算法的测量精确度进行验证。对实际点源图像生成已知RMS离焦值(0, 0.22, 0.44, 0.66 nm),从而产生具有偏移量的点源图像。使用模式法进行波前复原后,计算复原波面和残余波面的RMS值,用于比较频域上的互相关算法和传统质心算法的测量精度。结果显示,随着实际离焦值的增加,质心算法的测量误差呈现上升趋势,分别为0.0966 nm, 0.1378 nm, 0.1284 nm和0.1463 nm。频域互相关算法可以使夏克-哈特曼波前像差均方根(RMS)误差分别减少13%, 7%, 18%和14%,为空间引力波星载望远镜地面波前像差的高精度测试提供了重要参考。
Abstract
Accurate measurement and control of wavefront aberrations in space-based telescopes are key to achieving efficient space gravitational wave detection. This paper presents a method for measuring wavefront aberrations of space-based telescopes based on the Shack-Hartmann wavefront sensor. This method employs a cross-correlation algorithm in the frequency domain after frequency domain threshold denoising. The measurement accuracy of the algorithm is verified using a Shack-Hartmann wavefront sensor with 20×16 sub-apertures, microlens dimensions of 0.279 mm×0.279 mm, and a focal length of 34 mm. Point source images with known defocus RMS values (0, 0.22, 0.44, and 0.66 nm) are generated, producing point source images with displacements. After wavefront reconstruction using the modal method, the RMS values of the reconstructed and residual wavefronts are calculated, comparing the measurement accuracy of the cross-correlation algorithm in the frequency domain with the traditional centroid algorithm. The results show that as the actual defocus value increases, the measurement error of the centroid algorithm presents an upward trend, respectively at 0.0966 nm, 0.1378 nm, 0.1284 nm, and 0.1463 nm. The cross-correlation algorithm in the frequency domain can increase the measurement accuracy by 13%, 7%, 18%, and 14% respectively, providing an important reference for the high-precision testing of wavefront aberrations of space gravitational wave space-based telescopes on the ground.
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Overview
Overview: The successful detection of gravitational waves not only validate the general theory of relativity but also unveile previously undetectable cosmic events, opening new research directions for both physics and astronomy. Laser interferometers, characterized by their high sensitivity and broad frequency response, have become the primary method for gravitational wave detection. Due to the constraints imposed by terrestrial conditions, the frequency range for ground-based detection is quite limited, necessitating the exploration of space-based gravitational wave detection. Within this space-based detection framework, spaceborne telescopes serve as the core component. These telescopes require robust capabilities for interferometric laser transmission and reception, as well as high-precision tracking to accurately measure and detect gravitational wave events. Throughout their operation, these telescopes are affected by temperature variations in space, mechanical stresses or vibrations caused by launches or other space operations, thermal effects or expansions, and, over time, aging, degradation, or minor structural changes in the materials and components, all of which can result in wavefront aberrations. Such aberrations can directly influence the energy distribution and spatial position of the far-field light spot after being transmitted over hundreds of thousands of kilometers, subsequently limiting the interference quality and, in turn, the gravitational wave detection capability. To minimize the impact of wavefront aberrations on space-based gravitational wave detection, this paper introduces a frequency domain covariance algorithm for noise thresholding, replacing the threshold centroid algorithm for offset position estimation, and enhancing detection precision by incorporating multi-aperture multiplexing technology. By applying the frequency domain covariance algorithm and the threshold centroid algorithm to the slope measurement and wavefront reconstruction of actual point source images with added defocus values, we concluded that the former achieves higher measurement accuracy than the latter. The calculated defocus value and root mean square (RMS) of the residual wavefront further verified the computational precision of the relevant algorithms and their superior performance over the centroid algorithm. In comparison to the threshold centroid method, our approach exhibits greater accuracy in wavefront aberration measurement, achieving a precision of up to λ/3000. This study not only deepens our understanding of wavefront aberrations in gravitational wave detection but also paves the way for enhancing the precision and accuracy of gravitational wave detection.
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表 1 微透镜阵列及相机参数
Table 1. Microlens array and camera parameters
系统参数 值 波长 523 nm 相机位深 12 bits 像素尺寸 8.3 µm×8.3 µm 微透镜尺寸 0.279 mm×0.279 mm 焦距 34 mm 子孔径数 20×16 有效子孔径个数 140 -
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