Laser beam measurement using point diffraction interferometer（PDI） is studied by modeling and the factors that influence the measurement accuracy are investigated.First,zernike polynomial is used to fit aberrated wa...Laser beam measurement using point diffraction interferometer（PDI） is studied by modeling and the factors that influence the measurement accuracy are investigated.First,zernike polynomial is used to fit aberrated wavefront and the behavior of pinhole＇s diffraction with different aberrated wavefront is analysed.The following essential work on the PDI sensor is to get balance between intensity of the spherical reference wave and test wave.Then the optimum parameters for the model are obtained：wavelength of laser is 1 024 nm;pinhole＇s diameter is 2 μm;size of the focus spot is 20 μm;if gold（Au） is chosen as layer on film,its thickness should be 0.05 μm.The optimization results are only suited to the current PDI system,but the method presented is applicable to other configurations of high-accuracy PDI design.展开更多
A grating is an important element of a phase-shifting point diffraction interferometer, and the grating constant and duty cycle have a great impact on the interferometer, so the design of a grating becomes significant...A grating is an important element of a phase-shifting point diffraction interferometer, and the grating constant and duty cycle have a great impact on the interferometer, so the design of a grating becomes significant. In order to measure the projection objective with a numerical aperture of 0.2, we present a joint optimization method of a pinhole and grating based on scalar diffraction and the finite difference time domain method. The grating constant and the film thickness are selected, and the duty cycle of the grating is optimized. The results show that in the grating processing the material chromium is adopted, the thickness is 200 nm, and the grating constant is 15 μm. When the duty cycle is 55%, the interference fringe contrast is the greatest. The feasibility of the design result is further verified by experiment.展开更多
基金Sponsored by the National Basic Research Program of China("973"Program)(61397)
文摘Laser beam measurement using point diffraction interferometer（PDI） is studied by modeling and the factors that influence the measurement accuracy are investigated.First,zernike polynomial is used to fit aberrated wavefront and the behavior of pinhole＇s diffraction with different aberrated wavefront is analysed.The following essential work on the PDI sensor is to get balance between intensity of the spherical reference wave and test wave.Then the optimum parameters for the model are obtained：wavelength of laser is 1 024 nm;pinhole＇s diameter is 2 μm;size of the focus spot is 20 μm;if gold（Au） is chosen as layer on film,its thickness should be 0.05 μm.The optimization results are only suited to the current PDI system,but the method presented is applicable to other configurations of high-accuracy PDI design.
基金supported by the Major Scientific Instrument Development Project of the National Natural Science Foundation of China(No.11627808)the National Natural Science Foundation of China(No.61675026)the National Science and Technology
文摘A grating is an important element of a phase-shifting point diffraction interferometer, and the grating constant and duty cycle have a great impact on the interferometer, so the design of a grating becomes significant. In order to measure the projection objective with a numerical aperture of 0.2, we present a joint optimization method of a pinhole and grating based on scalar diffraction and the finite difference time domain method. The grating constant and the film thickness are selected, and the duty cycle of the grating is optimized. The results show that in the grating processing the material chromium is adopted, the thickness is 200 nm, and the grating constant is 15 μm. When the duty cycle is 55%, the interference fringe contrast is the greatest. The feasibility of the design result is further verified by experiment.
