Importance

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Abstract

The present invention provides a multi-layer optical disk, in which even if a wave length of read light is changed at a time of reproducing, both of reproduction signals from a first information memory layer and a second information memory layer have sufficient levels. In a multi-layer optical disk, in which a first information memory layer and a second information memory layer are sequentially film-formed on a substrate and information recorded on the first information memory layer and the second information memory layer are reproduced by irradiating read light from a substrate side, the first information memory layer and the second information memory layer can be reproduced by a first read light and a second read light which is shorter in wave length than this first read light, and the first information memory layer is made of material in which a refractive index n and an extinction coefficient k in a wave length area of the first read light comply with the following conditions: 0.ltoreq.k.ltoreq.0.25 n=.alpha.-k+2.8 (where .alpha. is a constant and 0.15.ltoreq..alpha..ltoreq.0.45)

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First Claim