The Research On Broad-band Laser Wavefront Measurement Technology For Transient Radial Shearing Interference

In the high-power laser systems,laser wavefront parameters are very important indicators for the evaluation of characteristics.As the scale of my country's inertial confinement fusion(ICF)high-energy laser installation becomes larger and larger,the requirements of the installation for the measurement and precise control of the single-shot laser wavefront in operation are getting higher and higher,so there is an urgent need for high-precision measurement of the transient wavefront.However,the traditional phase-shifting interferometry technology requires multiple phase-shifted interferogram,which cannot meet the requirement of transient measurement;the Fourier transform(FFT)based on the spatial carrier frequency cannot realize the customization of the sampling interval,and the accuracy of information extraction for broad-band light field is low.In order to realize the broad-band phase retrieval for the transient laser wavefront,an in-depth study on the technology of broad-band laser wavefront measurement for transient radial shearing interference is conducted.The research contents of this paper are as follows:1.The theoretical model of radial shearing interference fringes based on FFT of the spatial carrier frequency is systematically explained.It is mainly composed of four parts,namely: the principle of radial shearing interference,the calculation method of shearing wavefront based on FFT of the spatial carrier frequency,the method of phase unwrapping and iterative phase reconstruction.2.The research on the characteristics of phase retrieval for transient radial shearing interference mainly includes two parts:(1)The influence of the carrier frequency and the radial shearing ratio on the phase retrieved results are analyzed;the relationship between the shearing ratio and the relative sensitivity of the radial shearing interference and the measurement dynamic range are further studied.The optimal radial shearing ratio will increase with the increase of the PV value of the measured wavefront;the larger the radial shearing ratio,the larger the measurement dynamic range and lower the relative sensitivity;on the contrary,the smaller the shearing ratio,the smaller the dynamic range and higher the relative sensitivity;(2)The theoretical model of phase retrieved bandwidth of radial shearing interference based on spatial carrier frequency is established,in which the optimal carrier frequency and calculation window that can achieve broad-band phase retrieval are analyzed with emphasis.3.The broad-band phase retrieval method for transient radial shearing interference based on chirp Z transform(CZT)is proposed.By introducing CZT to realize the customization of the frequency domain interval,and combining the CZT algorithm and the proposed optimal carrier frequency and calculation window model,the corresponding wavefront phase retrieval algorithm is given in this paper.Through the simulation,it is concluded that the accuracy of the broad-band phase retrieval method using CZT is an order of magnitude higher than that of the traditional FFT.4.The experimental study of the research content of this paper is carried out,an experimental verification installation for the annular radial shearing interference is designed and built.The actual radial shearing interference fringes are analyzed by the broad-band phase retrieval method.Compared with the FFT method,the wavefront phase retrieved accuracy of this method is improved by an order of magnitude.And this conclusion is basically consistent with the theoretical simulation results.In addition,the broad-band phase retrieval method proposed in this paper is also suitable for other types of shearing interference.