[OPTICAL REVIEW Vol. 6, No. 5 (1999) 449-454]
Fractional Fringe Order Method Using Fourier Analysis for Absolute Measurement of Block Gauge Thickness
Minghong TSAI, Hongxin HUANG, Masahide ITOH and Toyohiko YATAGAI
Institute of Applied Physics, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8573 Japan
(Received April 23, 1999; Accepted June 17, 1999)
A fringe analysis method, which combines the Fourier transform with the fractional fringe order method for measuring the absolute thickness of a block gauge, is presented. An approximate integer part of the fringe order is estimated by mechanical measurements, and the fractional part is determined by Fourier analysis of the interferometric fringe patterns. The fringe patterns are obtained with a Michelson interferometer by illumination of several selected wavelengths, respectively. The use of the fractional fringe order method can determine accurately more than 2π phase jumps. The measured thickness of a block gauge is 5999115.0±0.7 nm, which is comparable with the standard thickness of 6 mm. The influence of wavelength and approximate integer part of fringe order on the measurement accuracy is discussed.
Key words : absolute measurement, fractional fringe order method, excess fraction, Fourier transformation, block gauge, 2π ambiguity