| As an important part of an optical system,the transmission wavefront of a transmission optical element directly affects the imaging quality of the system.High-precision transmission wavefront inspection technology can improve the processing quality of transmission optical elements,thus ensuring the imaging quality of the whole optical system.Among them,point diffraction interferometry is a high-precision wavefront measurement method for optical components.Its principle is to diffract a standard spherical wave with high accuracy through a pinhole as a reference wavefront,and the measurement accuracy can reach sub-nanometer scale,and it is of great significance for transmission wavefront detection of optical components with low cost and high stability.This paper combines birefringence polarization beam splitting technology,pointdiffraction interferometry and simultaneous phase-shifting technology to propose a wavefront dynamic point-diffraction interferometry measurement scheme based on birefringence polarization beam splitting,i.e.birefringence polarization beam splitting point-diffraction interferometer(BPBS-PDI).The incident beam is passed through a birefringent polarization beam splitting system to produce two output beams(o-beam and e-beam)with orthogonal polarization directions and small angular deviations.The o-beam and e-beam pass through the pinhole point-diffraction system as the reference beam and the test beam respectively.After the reference beam and the test beam pass through the synchronous phase-shifting interference system,four phase-shifting interferograms are finally obtained on the CCD.The image alignment algorithm,four-step phase-shifting algorithm and phase unwrapping algorithm are used to process the interferogram to obtain the recovered wavefront.To eliminate the influence of the transmission wavefront error of the whole system,especially the birefringent crystal,on the test results,this paper investigated the system error calibration method.The optical system without the test lens(TL)and with the test lens are tested separately,and the wavefront information of the test lens is obtained by processing the results of the two measurements.In this paper,based on the study of the principle and the system error calibration method,the structural design and error analysis of two key elements,the birefringence polarization beam splitter(BPBS)and the pinhole point diffraction plate(PPDP),are carried out,and the BPBSPDI experimental setup is built.Firstly,the system error of the optical system without the test lens is calibrated,then the test lens is added for wavefront measurement.Finally,the wavefront distribution,PV and RMS values of the test lens are obtained through the calculation of the two measurement results.Comparing the experimental results with the measurement results of the ZYGO interferometer,the results are very consistent.The PV value error is 0.013λ,the RMS value error is 0.005λ,which indicating that the BPBS-PDI wavefront measurement method can be used to measure the lens transmission wavefront with high accuracy. |
