<title>Absolute thickness measurement using automatic fractional fringe order method</title>

Abstract

The use of a broad-band interferometer and its fringe analysis method are presented in which the fractional fringe order method for measuring the absolute thickness. An approximate integer part of the fringe order is estimated by mechanical measurements, and the fractional part is determined by interferometric fringe pattern analysis. 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 2'r phase jumps. The influence of wavelength and approximate integer part offringe order on the measurement accuracy is discussed.