| 摘要 |
PROBLEM TO BE SOLVED: To prevent the lowering in an S/N ratio due to diffracted light beams used for no signal detection. SOLUTION: The diffracted light beams 103, 104 unnecessary for signal detection are made incident respectively on the surfaces 14, 15 different from the reflection surface 11 on which the diffracted light beam 102 used for signal detection is made incident. By working the surfaces 14, 15 to a coarse surface, or respectively providing reflection preventing films 14a, 15a on the surfaces 14, 15, the diffracted light beams 103, 104 are led to the outside of a light transmissivity block 3 while preventing the diffracted light beams 103, 104 from being reflected to the inside of the transmissivity block 3. |
