High Accuracy Compensator Design And Test Of Aspheric Surface By Iteration Method

Because aspheric components have more design freedom than sphericalcomponents, aspheric components are used widely to simplify system organizationand improve imaging quality in high numerical aperture projection lithographic lensand high accuracy cameras. Although aspheric components have so many advantages,high accuracy aspheric surface test is a problem for its long-range application all thetime. This paper focuses on an aspheric component of a high numerical apertureprojection lithographic lens. We use compensator method to test its surface. A relativeintegral method including compensator design and subsequent data processing isproposed. The following aspects are the primary coverage of this paper:1. Compensator design of aspheric surface. Based on the analysis of sagdeviation and sag slope of tested aspheric surface, we design the structure ofcompensator by MATLAB and an optical design software-ZEMAX. The major workis presented as follows:(a) The solution of initial compensator structure. A new method based oniteration idea is proposed to solve initial compensator structure made up of two lenses.This method is available to the case when the light source is parallel light. Firstlypartial structure parameters are assumed randomly and the other left two unknownparameters can be calculated when the absolute value of the sum of Seidel coefficients of the compensator and tested aspheric surface is smallest. Then with the help ofMATLAB we compare the Gauss image height of aspheric surface at the first surfaceof the compensator with the height of parallel light until the iterative error is less thanpreinstall. Thus the optimum height of parallel light is fixed. Finally we can retrysteps above mentioned to calculate the final initial compensator structure.(b) The optimization of initial compensator structure. When the refracting indexdata is matched to laboratory environment, a relative perfect compensator structurecan be got in double-pass beam path by wavefront merit function in ZEMAX.(c) Tolerance fit. The conventional tolerance is considered, such as design error,fabrication error and assemblage error. Material error, test error, environmental errorand adjustment error are also in consideration. Thus the systemic precision evaluationof aspheric surface test is realized.2. The compensator self-test. The refracting index data and the refracting indexhomogeneity data of blank glass are measured precisely. After the fabrication ofcompensator is completed, the radiuses of curvature of compensator are measured bycat eye-confocal method. The central thickness of compensator is measured byLenScan mirror alignment instrument. The final compensator structure is got afteroptic recalculation with the data from compensator self-test.3. The aspheric surface test and subsequent data processing. The flat referencelens from experimental flatform is calibrated absolutely by rotational translationalmethod. The distance and the aspheric surface test are accomplished base on theexperimental flatform. The wavefront error from refracting index homogeneity iscompensated.