| 摘要 |
<P>PROBLEM TO BE SOLVED: To stabilize a tracking signal and a focusing signal by removing inter-layer cross talk. <P>SOLUTION: A diffracting position on a semiconductor detector from the central region of a plural-region diffraction grating disposed on a return path of light reflected from a layer of interest is separated from an optical axis by farther than the diffracting position from around the diffraction grating, and thereby stray light from other layers is prevented from being incident into a sensitivity region of a peripheral region of the diffraction grating. Further, the area of the semiconductor detector is reduced by dividing the central region. <P>COPYRIGHT: (C)2012,JPO&INPIT |
