| 摘要 |
PURPOSE:To protect the reflective surface and at the same time to increase the degree of freedom of designing, by providing both a cladding layer and a light absorbing layer on the reflective surface of a prism that detects the reflected light of the beams focused on a subject to be irradiated. CONSTITUTION:The polarized beams emitted from a laser beam source 1 are condensed on a disk 6 via a collimator lens 2, a polarizing prism 3, a 1/4 wavelength plate 4 and an objective lens 5. The reflected light goes backward and reflected the prism 3 to be made incident to a reflective surface 11 of a detecting prism 10. Both a cladding layer 13 of silicone resin and a light absorbing layer 14 of the resin mixed with carbon black, etc. are coated on the surface 11. The light reflected on the surface 11 is made incident to a photodetector 12, and the distribution of light volume is detected to obtain a focal point error signal. In such way, the surface 11 can be protected and at the same time the degree of freedom can be increased for designing. |
