Development of PS-PDI(Phase-Shifting Point Diffraction Interferometer) with Optical Fibers

Abstract

Phase-Shifting Point Diffraction Interferometer (PS/PDI) with two optical fibers have been developed, which will be appropriate for the surface figure measurement of large aperture optics at sub-nanometer scale. To reduce the measurement error factors, fiber optic window (FOW) is used as a projection plane. A measurement accuracy of the PS/PDI is estimated with the interference pattern produced by the two optical fiber sources. The reduction of accuracy is mainly caused by an inhomogeneity of the FOW and an imperfection of optical alignment. If the errors are eliminated, the measurement accuracy of this system is less than 4nm P-V and 0.7nm rms.