| 摘要 |
PURPOSE:To reduce a measuring error induced by the wavelength variation of a light source by measuring the wavelenght variation of the light source by a reference optical system. CONSTITUTION:Light projected from the light source, e.g. a semiconductor laser L. D., is divided by a half mirror H.M.1, one is guided to a measuring interference optical system 21 and the other is guided to the reference optical system 22 constituted of a half mirror H.M.2, mirrors M1, M2, and a photodetector, e.g. a photodiode P. D. The ligh incident to the reference optical system 22 is divided into two optical pathes H.M.2-M1-H.M.2-M2-H.M.2 and synthesized again by the H.M.2 and the synthesized light is made incident ot the P. D. In said constitution, the output of the P. D. is output as a signal V3 indicating the quantity of wavelength variation through a wavelength variation measuring circuit 23. Thus, a measuring error due to the wavelength variation included in an output V2 of the measuring interference optical system 21 can be compensated by using the signal V3. |
