Design And Analysis Of Key Components Before The Reference Wave Point Diffraction Interferometer

A point diffraction interferometer(PDI) can be realized by using the near-perfect spherical wave diffracted by a pinhole as reference wavefront. In order to measure laser wavefront, based on traditional PDI, a collimated wavefront testing system is designed and set up in this paper. The property and core parameters of the key components are studied.Based on the scalar diffraction theory, using Fresnel wavelet superposition principle, far-field intensity distribution of the reference wavefront diffracted by a pinhole is accessed in order to obtain clear, bright and stable interference fringes, to ensure the far-field intensity matching between the interference beams. The intensity changes is analyzed with different pinhole diameter, pinhole transverse defocus, and pinhole axial defocus. The simulation results show that the smaller is the pinhole diameter, the more uniform is light intensity. When the pinhole moves away from the focus either transverse or axial, the value changes in light intensity is not monotonic.Based on Fresnel diffraction integral formula, the factors which influence the quality of reference wavefront are analyzed. The factors include pinhole diameter deviation, pinhole shape deviation, aberrations of the incident wavefront, the pinhole transverse defocus and the pinhole axial defocus. The results show that aberrations of the incident wavefront (mainly coma and astigmatism) and pinhole transverse defocus have a greater influence on the accuracy of the system.The PDI plate parameters are measured using white light interference microscope. The results show that when measuring the pinhole with the size of micrometers, the method based on High Definition Vertical Scanning Interferometry (HDVSI) is better than that based on Vertical Scanning Interferometry (VSI). The wavefront diffracted by10um pinhole is measured. The experimental results are compared with the simulation results which show good coincidence with the deviation of0.0136λ(PV) and0.0084λ(RMS). The error sources are analyzed in detail.