Method and apparatus for measuring minute displacement by subject light diffracted and reflected from a grating to heterodyne interference

摘要

The present invention resides in method and apparatus for measuring a minute displacement, comprising applying a light of a first wavelength at a predetermined angle to a diffraction grating formed on an object whose position is to be detected, subjecting each of the resulting diffracted light and regular reflected light and a light of a second wavelength different from the first wavelength to heterodyne interference with each other to generate a measurement signal and a reference signal, and measuring a phase difference between the measurement signal and the reference signal to thereby determine a minute displacement of the object.