| Shack-Hartmann wavefront measurement technology has the advantages of simplicity,efficiency and large dynamic range in dynamic measurement regardless of the coherence of light source.Therefore,it has been widely used in adaptive optics,optical processing and alignment,ophthalmology and laser parameter diagnosis.With the precision of ultra-precision optical components processing and the scale of high-power laser devices increasing,high-precision wavefront measurement technology is required.According to the Shack-Hartmann wavefront measurement principle,the measurement accuracy is affected mainly by wavefront slope measurement accuracy and reconstruction algorithm accuracy.At the same time,the assembly error of the Shack-Hartmann wavefront sensor and the calibration accuracy of the parameters will also seriously affect the accuracy of the wavefront measurement.Now the evaluating methods for the accuracy of the Shack-Hartmann wavefront measurement still can not match the evaluation for manufacture precision of high quality optical surface and wavefront distortion measurement precision in high power laser facility.Therefore,how to comprehensively and objectively evaluate and improve the accuracy of the Shack-Hartmann wavefront measurement to meet the great demand for high-precision wavefront measurement is a scientific problem that needs to be solved urgently.Firstly,the frequency response of the Shack-Hartmann wavefront reconstruction is studied,and the theoretical models of the frequency response function for the traditional zonal method and mode method are derived.Based on that,wavefront reconstruction method with optimized frequency response was proposed and the accuracy for full-band wavefront measurement was improved.Meanwhile the assembly error and calibration method of the Shack-Hartmann wavefront sensor were studied..Finally,based on wavefront sensor with optimized frequency response,a method for laser far-field focal spot reconstruction was proposed.The main contents are as follows:1.The low-pass filtering effect on actual wavefront information arising from microlens array discrete sampling and wavefront reconstruction model is theoretically analyzed.The theoretical models of the system frequency response function for the traditional zonal method and mode method are derived in spatial frequency domain.The accuracy of the theoretical model is verified by theoretical simulation.And it is shown that the frequency response of the traditional wavefront reconstruction method is not unit uniform response,that is,varying degrees of distortion arises during the reconstruction of different spatial frequency component,thus affecting the accuracy of the wavefront measurement.The zonal method has better frequency response in the middle and high frequency parts than the mode method.2.The theoretical frequency response model of wavefront reconstruction based on the Simpson quadrature method is derived.The regularization term is introduced to eliminate the singularity,and the Momentum Gradient Descent(MGD)algorithm is used to determine the optimal regularization factor and then wavefront reconstruction model with optimized frequency response is obtained.Beyond that,the band-limited wavefront reconstruction algorithm based on the optimized Simpson model is designed.Then,the error of the wavefront reconstruction algorithm is theoretically simulated and analyzed.Finally,an experimental device based on liquid crystal spatial light modulator(LC-SLM)is designed and built.The comparison between the frequency response of the proposed method and that of the traditional method is carried out,and the superiority of the proposed method is verified.3.The theoretical models of four assembly errors for the Shack-Hartmann wavefrot sensor are derived.The theoretical simulation and analysis are carried out.And the method of reducing the assembly error is proposed and verified by experiments.Then,the calibration method of the Shack-Hartmann wavefront sensor based on spherical wave is studied,and the theoretical model and algorithm of calibration are established.The calibration experimental device is built to calibrate the designed Shack-Hartmann wavefront sensor.Finally,the uncertainty of the calibration is analyzed and calculated.The results show that the proposed method is feasible for calibration.4.A method for far-field focal spot reconstruction based on the Shack-Hartmann wavefront measurement with optimized frequency response is proposed.The reconstruction algorithm of laser focal spot is designed.The accuracy of far-field focal spot reconstruction is improved by combing the optimized wavefront reconstruction and the cubic B-spline interpolation surface algorithm.The theoretical simulation and analysis of laser far field focal spot reconstruction algorithm is completed.The laser far-field focal spot diagnosis experimental device is designed and built.The far-field focal spot measurement results of the proposed method and the traditional method are compared,and the superiority of the proposed method is verified. |
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