| 摘要 |
PURPOSE:To prevent the generation of a measuring error by excluding the influence of multiple reflection between a surface to be measured and a reference surface, by providing a polarization means on the way of a beam path, to which reflected beam at the surface to be measured is returned, to block an unnecessary component while transmitting only a necessary component. CONSTITUTION:Beam from a laser oscillator 2 is allowed to irradiate a reflective film 24 constituting a surface 21 to be measured and a reference surface through a beam splitter 3 and the displacement of the surface 21 to be measured is measured by utilizing the interference of reflected beams B2, B1. In thus constituted displacement measuring apparatus, 1/4 wavelength plates 22, 23 are provided to the transmission beam path of the beam splitter 3 and the reflective film 24 is attached to the back surface of the 1/4 wavelength plate 22. By this mechanism, only a component having a polarization surface parallel to a paper surface in the return beam transmits a polarization plate 25 and, therefore, displacement measurement receiving no influence caused by the disturbance in the polarization state of reflected beam can be performed and an error caused by multiple reflection between the surface 21 to be measured and the reference surface (reflective film) 24 can be removed. |
