Kenichi HIBINO^*, Yangjin KIM¹, Sangyu LEE², Yohan KONDO, Naohiko SUGITA¹, and Mamoru MITSUISHI¹

National Institute of Industrial Science and Technology, Tsukuba, Ibaraki 305-8563, Japan ¹The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan ²LG Electronics, Pyeongtaek, Gyeonggi 451-713, Korea

(Received January 31, 2012; Revised April 20, 2012; Accepted April 26, 2012)

The absolute optical thickness and the surface shape of a glass plate of 7-in. square and 3.1 mm thick was simultaneously measured by three-surface interferometry using a wavelength tuning Fizeau interferometer. The wavelength of a tunable diode laser is scanned linearly from 632 to 642 nm, at which the initial and the final phases of the interference fringes for the surface shape and for the optical thickness were separated and measured by a tunable phase-shifting technique. The number of phase variations in the interference fringes during the scanning is counted by discrete Fourier analysis, in which systematic errors caused by a nonlinearity in the wavelength scanning is corrected by a correlation analysis between the observed and theoretical interference fringes. Experimental results demonstrate that the systematic errors in the measured value were 15 nm for the surface shape and 0.6 μm for the absolute optical thickness.

Key words: phase measurement, Fizeau interferometer, wavelength-tuning, absolute optical thickness, surface shape

^*E-mail address: k.hibino@aist.go.jp