| 摘要 |
PURPOSE:To perform measurement at plural angles of incidence without moving an optical system by mixing frequency-shifted light with light reflected by a film to be measured by the optical system. CONSTITUTION:Light from a laser light source 20 is branched into two by a half-mirror 22 and one light beam is projected on the film 2 to be measured through a beam expander 23. Further, the other output light beam of the half- mirror 22 is shifted in frequency by an acoustooptic modulator 27 and the shifted light is reflected by a mirror 29 and its beam diameter is expanded by an expander 30, so that the light is converted into parallel light. This parallel light is reflected by a mirror 31, transmitted through a half-mirror 24, and mixed with the light reflected by the film 2 to be measured to obtain their beat frequency, which is incident on a photodetector 26. The photodetector 26 converts the intensity of the incident light into an electric signal. Consequently, the measuring operation is performed at plural angles of incident without moving the optical system.
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