Research On Absolute Inspection Technology Of Large Aperture Interferometer Based On Standard Liquid Level

The calibration of interferometer system error becomes more and more important with the improvement of precision manufacturing industry's requirement of optical element surface.Among them,the liquid reference method is an absolute test method with high-precision and classic.In this paper,the interferometric method is used to complete the study of the dynamic characteristics of the liquid flat,and a standard liquid reference is established,and the system error calibration and measurement of the large-aperture vertical interferometer are got by using the liquid reference.First,two phase-shifting interferometry methods are proposed for the unstable state and the steady state of the liquid flat.A dynamic Fizeau interferometer system is constructed by using a point light source ex-situ interferometric method to perform transient measurement under the unstable state of the liquid flat,analyze the dynamic characteristics of the liquid flat,and establish a liquid reference.A large-aperture vertical Fizeau interferometer was built using the wavelength-tuning interferometric method to analyze the liquid surface characteristics in a steady state,and complete the absolute test of the liquid surface.Second,the study explored how to build a high-precision standard liquid flat.The liquid standard directly affects the accuracy of the absolute liquid flat inspection,so the establishment of the liquid standard is an extremely critical step in the absolute liquid level inspection.By analyzing the properties of liquid and liquid flat,the influence of liquid material,viscosity and thickness on the stability of liquid flat and the influence of material,size and damping island of liquid flat on the flatness of liquid level were investigated,and the evaluation index of liquid flat stability was discussed.The final liquid material is 100 cs simethicone,the thickness is 2mm or slightly greater than 2mm.The effective aperture of the interferometer is less than 90% of the diameter of the liquid pan.The third is the analysis and discussion of liquid surface environmental protection technology.Different from crystal flat,liquid flat is very sensitive to external environment.Temperature and humidity,air flow and vibration all have great influence on the stability and flatness of liquid flat.Therefore,the influence of environmental temperature and humidity change on the smoothness and stability of the liquid flat is obtained through specific theoretical analysis and experimental verification.Precision air conditioning system is adopted to control the fluctuation of ambient temperature within 0.1?,and vibration isolation device and windshield are added to obtain the final environmental conditions of liquid flat that meet the requirements.In the end,the large-aperture Fizeau interferometer was calibrated by using the established high precision liquid reference At the same time,the repeatability and reproducibility of the experiment are discussed,and the influence of system error and experimental error is analyzed.The experiment obtained the PV value of the ?300mm large-aperture vertical Fizeau interferometer calibration result is 23.2nm,RMS value is 3.4nm.And two different liquid reference benchmarks were used to carry out the absolute liquid reference inspection respectively,and the wave-front residual PV value of the two measurement results was 5.8nm which proved the reliability of the liquid reference absolute inspection method.Finally,the results of the absolute inspection of the liquid reference and the absolute inspection of the crystal are compared and analyzed,and the residual wavefront PV value of the two methods is6.1nm,which proves the accuracy of the absolute inspection method of the liquid flat.