| 摘要 |
PROBLEM TO BE SOLVED: To facilitate thickness measurement of a light transmission layer of an optical recording medium, such as an optical disk, without degrading the light efficiency of a laser beam for recording/reproducing. SOLUTION: The optical recording medium 10 has a supporting substrate 12. am information recording surface 14 and the light transmission layer 16 and a half-mirror coat 18 is formed on the surface of the light transmission layer 16 in a region corresponding to a lead-in area 14A of the information recording surface 14. The optical recording medium is so formed that, when the half-mirror coat 18 is irradiated with the laser beam for recording/ reproducing, the quantity of the return light reflected there and the quantity of the return light transmitted through the half-mirror coat 18, reflected in the lead-in area A of the information recording surface 14 and emitted again past the half-mirror coat 18 are made nearly equal to each other. |
