[OPTICAL REVIEW Vol. 14, No. 6 (2007) 401-405]
© 2007 The Optical Society of Japan

Measurement Accuracy in Phase-Shifting Point Diffraction Interferometer with Two Optical Fibers

Toshiaki MATSUURA, Satoru OKAGAKI, Takaaki NAKAMURA, Yasushi OSHIKANE, Haruyuki INOUE, Motohiro NAKANO, and Toshihiko KATAOKA

Division of Precision Science and Technology and Applied Physics, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan

(Received January 29, 2007; Accepted July 4, 2007)

A phase-shifting point diffraction interferometer (PS/PDI) with point sources of two single mode optical fibers has been developed, which will be appropriate for the surface figure measurement of large aperture optics on a sub-nanometer scale. To reduce the measurement error factors, a fiber optic plate (FOP) is used as a projection plane for interference pattern. Errors caused by imperfection of optical alignment, such as position of point sources and tilt of FOP, are minimized by analyzing the measured phase data with an original method. Measurement accuracy in the PS/PDI is estimated with the interference pattern produced by the two optical fiber sources. If inhomogeneity of the FOP and a systematic error of the PS/PDI are eliminated, the measurement accuracy of the present system is estimated to be less than 4 nm P-V and 0.7 nm rms, respectively, at a measurement wavelength of 632.8 nm.

Key words: point diffraction interferometry, phase-shifting interferometry, surface figure measurement, diffracted spherical wavefront, single-mode optical fiber, fiber optic plate