| 摘要 |
PURPOSE: To measure the thickness fluctuations of a thin plate material with high accuracy, over a wide range on the basis of relatively large spot diameter of 0.5-2 mm. CONSTITUTION: A polarizing beam splitter 20 for dividing the laser beam, which is emitted from a laser generator 11 and transmitted through an isolator 16, into measuring beam and reference beam. One-quarter wavelength plates 21 are provided between the polarizing beam splitter 20 and a measuring surface, and between the polarizing beam splitter 20 and a reference surface. Condensing reflection means 23 and 24 for condensing the measuring beam successively reflected by the measuring surface and the polarizing beam splitter 20 and the reference beam reflected by the reference surface and transmitted through the polarizing beam splitter 20 are provided. A half mirror 19 for reflecting the measuring beam and reference beam, which is returned from the polarizing beam splitter 20, is provided. A beam-receiving part 13 for receiving the measuring beam and reference beam reflected by the half mirror 19 to made them interfere with each other and converting a change in interference intensity to an electrical signal and counting the electrical signal to measure the flatness of the measuring surface is provided.
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