| 摘要 |
PURPOSE: To provide a structure having an effect of suppressing the interference between the reflected light on the surface of an optical disk having a two-layered structure on one side and the reflected light on a lower side recording layer. CONSTITUTION: This disk is provided with an upper side recording layer (first recording layer) in a segment of (h) in the distance from the disk surface, is provided with the lower side recording layer (second recording layer) in a segment of h+Δh in the distance from the disk surface, is provided with an intermediate layer of a thickness Δh between the upper side recording layer and the lower side recording layer and is provided with a cover layer of a thickness (h) between the upper side recording layer and the disk surface. The thickness Δh of the intermediate layer is regulated in such a manner that the coherent distance (Lc) determined by the central wavelength λ0 of the exit light power spectra of the light source of the laser beam with which the disk is cast and the half band width Δλ thereof is smaller than the optical path difference (ΔL) between the light u0 directly reflected by the cover layer surface and the light u2 which is transmitted through the cover layer and the intermediate layer, is reflected by the lower side recording layer and is then emitted again from the cover layer.
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