| 摘要 |
PURPOSE:To measure a minute displacement with reduced influences of the distribution of the air density by a method wherein the light is incident with about 1/2 the primary angle of diffraction to a diffraction grating, the generated diffraction light, regularly reflected light and a light of a different wavelength are subjected to heterodyning interference thereby to generate a measuring signal and a reference signal, and the phase difference of the signals is obtained. CONSTITUTION:A light projected from a linear polarizing laser 11 is divided into three. Two of the luminous fluxes are brought into a diffraction grating 7 as a light LB1 with approximately 1/2 the primary angle of diffraction, so that the primary diffraction light and regularly reflecting light are generated. The other luminous flux is divided into two as a light LB2 while the wavelength is made slightly different. When the primary diffraction light and regularly reflected light of the light LB1 and the light LB2 are subjected to heterodyning interference, a measuring signal and a reference signal are optically detected at 91, 92. The phase difference of the signals is obtained. In this manner, the optical path of the light LB1 for forming the measuring signal is made close to the optical path of the light LB1 for obtaining the reference signal, and also the optical path of the light LB2 for the two signals is rendered close. Accordingly, it becomes possible to measure the displacement hardly influenced by the distribution of the air density. |
