Study On Aspheric Surface Testing And Contribution Of Temperature Change On Surface Deformation In Absolute Test

The fringe of Fizeau interferometer is produced by the interference between reference wave front and test wave front. The major aspects affecting the accuracy of Fizeau interferometer are the accuracy of reference surface and the error from environment difference in standard calibration and test environment. Fundamental and critical problems about calibration of surface thermal distortion for absolute test and aspheric testing were focused. The following aspects are the major results of the work:(1).The model of thermal distortion for absolute test is founded, Detailed work presented as follows:a. The finite element model of auxiliary plane surface is built to simulate the distortion of the actual surface error, and the accuracy of the model is proved;b. The Zernike fitting algorithm is used to fit the thermal distorting surface, and the surface distortion at the nodal points are fitted using two dimensional Shepard fitting method and the finite element model of plane surface;c. According to the relationship Between Zernike polynomials and Seidel aberrations, the variation law of thermal deforming wave front in different surface aberrations modes is analyzed and the thermal wave front change is calibrated. Initial surface distributions are given in the modes of Seidel aberrations, which can associated with Zernike polynomials in expressing wave front change. The association between Zernike polynomials and Seidel aberrations is instructive in improving the test ability and appropriate thermal distortion model adopted for developing high accuracy Fizeau interferometer to evaluate the performance of surface thermal distortion with different materials and different temperature changes.(2).Reference surface model is built and the influence of environment factors including temperature, gravity and clamping force are studied of the K9、fused silica and zerodur three materials. The Gram-Schmidt fitting was used to fit the deformation of the reference surface in representation of the Zernike coefficients. The deformation of the reference plate caused by gravity, clamping force, temperature and just gravity, clamping force of three materials were compared. The contribution of the thermal deformation and the change in Zernike coefficients induced by temperature change of three materials were compared. The study result can be used in different clamping support modes and the model of the thermal deformation was created and the corresponding aberration mode of the reference surface was analyzed which make the separation of the deformation caused by temperature became possible, so that the accuracy of the test can be enhanced.(3).Various aspheric surface testing methods were compared, Offner null compensator was adopted to test the aspheric surface in the lithography projecting lens at last. Primary distribution of the tolerance and error budget of the system was presented based on the accuracy of measuring apparatus.