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Abstract

A light interferometer has an interferometer portion for interfering a measuring light and a reference light, and a light signal processing portion for processing a signal according to an interference signal which changes according to the change of an optical path length of the measuring light. The interferometer portion has a first light source for generating a coherent light, a light interference portion for dividing the coherent light emitted by the first light source into a reference light and a measuring light in order to introduce the measuring light to an object, making the measuring light reflected by the object and the reference light interfered with each other and introducing thereof to a photo detector, and an optical path length periodically changing means for periodically changing the difference of an optical path length of the reference light with respect to the optical path length of the measuring light relatively at a constant amplitude. The light signal processing portion has a second light source for generating a coherent light, a collimate lens portion for collimating the coherent light emitted by the second light source, a space modulating portion for diffracting the coherent light outgoing from the collimate lens portion, a Fourier transforming portion for transforming the diffracted coherent light, and two photodetectors disposed on at a spot corresponding to a frequency composition equivalent to a frequency of the optical path length periodically changing means and the other at a spot corresponding to a frequency composition two times the first-mentioned frequency composition in order to extract these frequency compositions out of frequency compositions which have been decomposed in frequency spectral by the Fourier transforming portion.

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First Claim