| 摘要 |
PURPOSE:To obtain desired optical characteristics by making the interval between first and third recording layers an integral multiple of the effective wavelength so that the degree of freedom of changes in reproducing light quantity is enhanced for multi-valued recording. CONSTITUTION:On a transparent substrate 1, there are successively formed a first recording layer 2, first transparent layer 3, second recording layer 4, second transparent layer 5, and third recording layer 6. The layer 2 has low photosensitivity than the layer and higher than the layer 5. The layers 2, 4, 6 consist of Al, Te, Au thin films, respectively, for pit-type recording layers. The layer 3 and 5 are ZnS thin films, and these films are formed in a manner that the interval between the layer 2 and the layer 6 is mlambda/2n, wherein m is a natural number, lambda is the wavelength of the light source, and n is the refractive index of the transparent layer. By irradiating or not irradiating the recording layer light from the substrate side 1 to the recording medium, four-value states A-D are obtd. for a molten or not molten state of each recording layer. Therefore, reproducing light a-d is obtd. corresponding to these states. Phases of the reflected light coincide well to make an intense beam and to give rather large reproducing light quantity. |
