| 摘要 |
PURPOSE:To detect exactly an edge by irradiating a laser beam onto the surface to be measured, so that its reflected beam is made incident on a split photodetector. CONSTITUTION:A laser light which has been emitted from a laser diode 1 is shaped through a collimator lens 2, and made incident on a polarized beam splitter 3. The light beam in this case is a P polarized light, therefore, passes through the splitter 3 and changed to a circularly polarized light by a 1/4 wavelength plate 4, reduced by an objective lens 5, and a laser spot is formed on the surface to be measured 6. The light beam which has been reflected therein is changed to a circularly polarized light of a reverse turn, and made incident on the splitter 3 through the lens 5 and the wavelength plate 4. The light beam which has passed through this wavelength plate 4 becomes an S polarized light and reflected by the splitter 3, made incident on a beam splitter 7 and split into two beams. One beam passes through a focusing lens 8, and thereafter, forms a spot on the photodetecting surface of a two-split photodiode 9, and the other beam passes through a cylindrical lens 10, and thereafter, forms a spot on the photodetecting surface of a two-split photodiode 11. In this way, when an edge axists, it can be detected by a variation of the photodetecting quantity.
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