JPS6431007A - Measuring method of incident angle - Google Patents

Abstract

PURPOSE:To enable the highly precise measurement of an incident angle of beam on a substance, by a method wherein a diffraction grating is provided on the substance, one of diffracted beams of an incident beam caused by the diffraction grating is reflected, the reflected beam and at least one diffracted beam are made to interface with each other, and the beam intensity of a composite beam thus formed is measured. CONSTITUTION:A reflected beam R is obtained by making a diffracted beam D2 reflected by a reflector 2, and it is made to advance in the same direction with that of another diffracted beam D1 so that the beams D1 and R are made to interfere with each other. The phase of the beam R is delayed by the length of its optical path because of its going through the reflector 2, and a phase delay DELTApsi thereof is determined by a distance to the reflector 2 and a diffraction angle theta. The angle thetais varied in accordance with variation in an incident angle psi, and the incident angle psican be measured by a method wherein the beams R and D1 are made to interfere with each other and the phase delay DELTApsi is introduced into a detector 3 and measured from the variation in the intensity of a composite beam U of said lights. Accordingly, since the diffracted beam is used, the incident angle can be measured with high precision without affecting virtually a beam transmitted directly through a substance 1 and a beam reflected directly on the substance 1.