Research On Phase Shifting Technique Of ?300mm Vertical Fizeau Interferometer And Its Key Techniques

Optical interferometry is the most commonly used method for measuring optical plane elements.Most of the existing large aperture interferometers are based on temporal phase shifting techniques.Although these techniques are mature and stable,they are easily affected by environmental factors.Spatial phase-shifting interferometry isusually based onpolarization phase shifting techniques,which is easily affected by the stress of large aperture optical elements.In order to solve the above problems,a 300 mm aperture vertical Fizeau interferometer is developed in this paper,which uses temporal phase shifting interferometry and spatial phase shifting dynamic interferometry integratedly.The phase shifting principle of 300 mm aperture vertical Fizeau interferometer is studied.The principle of wavelength tuning temporal phase shifting interferometry is introduced,phase shifts is introduced into the interferograms by changing the output wavelength of the wavelength tunable laser.The principle of spatial phase shifting interferometry based on inclination angle is proposed.A point light source deviated from the optical axis generate a certain inclination angle between the collimated beam and the optical axis and introduce phase shifts into the interferograms.Four point light sources with the same optical characteristics are used to realize simultaneous phase-shifting.A 300 mm aperture vertical Fizeau interferometer system was designed and constructed.The optical path structure of the interferometer is designed,and the interference system is divided into multiple modules and analyzed sequentially.In the light source module,the laser used for wavelength tuning phase shifting are selected.In order to provide four point light sources for simultaneous phase-shifting interferometry based on inclination angles deflection,two types of light source systems of grating beam splitting and fiber beam splitting are designed and compared.In the interference module,an aspheric single lens is designed as the collimating objective of the interferometer.The reference mirror is parametrically modeled and the surface deformations under different dispensing methods are analyzed by the finite element analysis software.In the imaging system module,lens array is used to design the imaging optical path and four separated phase-shifting interferograms are obtained simultaneously.In the software algorithm module,the random phase shifting algorithm is studied,and its ability to suppress phase shifting errors is compared with the fourstep phase shifting algorithm.A spatial interferograms registration algorithm is proposed.In the environmental support system module,a multistage anti-vibration system is used to isolate the vibration and a constant temperature environment is established with the air conditioning system to create a stable measurement environment.The completed interferometer can realize two kind of phase shifting interferometry.Experiments are performed on the precision of the 300 mm aperture vertical Fizeau interferometer.The repeated test results show that the repeatability of the PV value of the interferometer is better than 0.005?,and the repeatability of the RMS value is better than 0.001?.A scanning method of cube-corner prism is proposed to test the emergent wavefront of the interferometer,and the results shows that the PV value and the RMS value is 0.1349? and0.0454? respectively.Comparative experiments conducted on ZYGO interferometer prove the correctness of the method.The surface shape of the reference plane was calibrated by the liquid absolute test method.The calibration results of PV value and RMS value are 0.060? and 0007?,which have good repeatability and reproducibility.The system error of 300 mm aperture vertical Fizeau interferometer is analyzed.The relationship between the length of the interference cavity and the off-axis quantity of the point light source array is calculated.The errors introduced by the off-axis of the point light source array are analyzed,and the selection of the size of the point light source array is discussed.The ripple error caused by the inconsistent intensity of the point light source is analyzed by numerical simulation,and the error tolerance is given.Discussed the phase shift error caused by the tilt of the test mirror.