Large dynamic range Shack-Hartmann wavefront sensor based on adaptive spot matching

The Shack-Hartmann wavefront sensor(SHWS)is widely used for high-speed,precise,and stable wavefront measurements.However,conventional SHWSs encounter a limitation in that the focused spot from each microlens is restricted to a single microlens,leading to a limited dynamic range.Herein,we propose an adaptive spot matching(ASM)-based SHWS to extend the dynamic range.This approach involves seeking an incident wavefront that best matches the detected spot distribution by employing a Hausdorff-distance-based nearest-distance matching strategy.The ASM-SHWS enables comprehensive spot matching across the entire imaging plane without requiring initial spot correspondences.Furthermore,due to its global matching capability,ASM-SHWS can maintain its capacity even if a portion of the spots are missing.Experiments showed that the ASM-SHWS could measure a high-curvature spherical wavefront with a local slope of 204.97 mrad,despite a 12.5%absence of spots.This value exceeds that of the conventional SHWS by a factor of 14.81.

Accuracy characterization of Shack-Hartmann sensor with residual error removal in spherical wavefront calibration

The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the sensor itself.In this study,based on the principle of spherical wavefront calibration,a pinhole with a diameter of 1μm was used to generate spherical wavefronts with extremely small wavefront errors,with residual aberrations of 1.0×10^(−4)λRMS,providing a high-accuracy reference wavefront.In the first step of SHWFS calibration,we demonstrated a modified method to solve for three important parameters(f,the focal length of the microlens array(MLA),p,the sub-aperture size of the MLA,and s,the pixel size of the photodetector)to scale the measured SHWFS results.With only three iterations in the calculation,these parameters can be determined as exact values,with convergence to an acceptable accuracy.For a simple SHWFS with an MLA of 128×128 sub-apertures in a square configuration and a focal length of 2.8 mm,a measurement accuracy of 5.0×10^(−3)λRMS was achieved across the full pupil diameter of 13.8 mm with the proposed spherical wavefront calibration.The accuracy was dependent on the residual errors induced in manufacturing and assembly of the SHWFS.After removing these residual errors in the measured wavefront results,the accuracy of the SHWFS increased to 1.0×10^(−3)λRMS,with measured wavefronts in the range ofλ/4.Mid-term stability of wavefront measurements was confirmed,with residual deviations of 8.04×10^(−5)λPV and 7.94×10^(−5)λRMS.This study demonstrates that the modified calibration method for a high-accuracy spherical wavefront generated from a micrometer-scale pinhole can effectively improve the accuracy of an SHWFS.Further accuracy improvement was verified with correction of residual errors,making the method suitable for challenging wavefront measurements such as in lithography lenses,astronomical telescope systems,and adaptive optics.

星敏感器离焦像点半径最优值的确定方法

分析了不同离焦像点半径及不同噪声强度下的星敏感器质心定位误差,建立了质心定位误差关于离焦像点半径和噪声强度的函数模型,在质心定位精度确定的条件下得到了离焦像点最优高斯半径与背景噪声强度的一元函数关系。仿真实验表明,在给定的质心定位精度下,最优高斯半径与噪声强度近似服从抛物线关系,统计出噪声强度后即可得到最优的像点高斯半径值。

对地观测平台恒星敏感器离焦成像折中设计分析

从对地观测平台角秒量级姿态确定需求出发，在构建星敏感器惯性系成像模型的基础上指出，恒星在成像面上的定位误差是星敏感器姿态确定误差的主要来源。同时，结合理想光学系统离焦模型，分析了星敏感器主要性能指标间的量化关系，并给出了成像面定位误差最低限。仿真结果表明，从优化系统性能考虑，成像模糊区直径为2～3个像元的配置是利用星敏感器焦平面的“轻微离焦”来实现亚像元定位的最佳方案，定位误差可达0．2个像元，能够满足星敏感器惯性姿态确定精度4＂～5＂的要求。理论分析和数值仿真结果可为后续星敏感器指标的提出及仪器设计提供技术参考。

基于离焦型夏克-哈特曼传感器的定量相位成像技术

提出了一种基于离焦型夏克-哈特曼传感器的定量相位成像技术。该技术利用离焦型夏克-哈特曼波前传感器记录两种不同波长的光的照射下的强度分布图,采用双波长相位恢复算法进行相位恢复,获得了透过相位物体的数字光场,实现了纯相位物体成像。数值模拟结果表明该定量相位成像技术方法简单、精度高、收敛速度快,是一种非常具有潜力的定量相位成像技术。

基于平行光管的星敏感器焦平面离焦距离检测设备设计及其误差分析

在星敏感器中,使用离焦成像的方式实现对恒星的成像,成像质量直接影响着测量定位精度。而星敏感器光学系统和图像传感器之间的离焦距离是寻找最优成像的重要参数。为了准确测得此离焦距离,设计了基于平行光管的星敏感器焦平面离焦距离检测设备,并针对设备设计原理中影响检测精度的各项因素进行误差分析。首先,在检测原理公式的基础之上,给出主要设计参数。其次,结合检测原理公式分析主要影响因素,即平行光管焦距误差、星敏光学系统焦距误差和直线位移台运动分辨率,并针对不同取值范围进行了仿真,验证了设计参数的理论合理性。

Wave-front correction of high-intensity fs laser beams by using closed-loop adaptive optics system

We developed an adaptive optics system to correct the wave-front distortion of an intense fs laser beam from our multi-TW laser system, Jiguang II. In this paper, the instruments of the adaptive optical system are described and the experimental results of the closed-loop wave-front correction are presented. A distorted laser wave-front of 20 wavelengths of P-V values was corrected to 0.15 wavelength of P-V values. The beam quality of the laser system varies from 3.5 diffraction limit to 1.5 diffraction limit.

Surface Measurement Using Compressed Wavefront Sensing

Compressed sensing leverages the sparsity of signals to reduce the amount of measurements required for its reconstruction. The Shack-Hartmann wavefront sensor meanwhile is a flexible sensor where its sensitivity and dynamic range can be adjusted based on applications. An investigation is done by using compressed sensing in surface measurements with the Shack-Hartmann wavefront sensor. The results show that compressed sensing paired with the Shack-Hartmann wavefront sensor can reliably measure surfaces accurately. The performance of compressed sensing is compared with those of the iterative modal-based wavefront reconstruction and Fourier demodulation of Shack-Hartmann spot images. Compressed sensing performs comparably to the modal based iterative wavefront reconstruction in both simulation and experiment while performing better than the Fourier demodulation in simulation.