| 摘要 |
PURPOSE:To make the reproduction of a pit which is smaller than the radius of a laser light spot possible by making an information unit out of either one or both of a recording layer which is adjacent to the forming part of a thermal diffusion layer and one which is adjacent to the non-forming part. CONSTITUTION:A first minute area alpha1 which is formed in adjacent to the thermal diffusion layer N in order to enlarge heat radiation and a second minute area alpha2 which is not formed in adjacent to the layer N are provided. Then, either one of the areas alpha1 or alpha2 or both are made an information unit. Also, the radius of the areas alpha1, alpha2 is each made smaller than the spot radius S of a laser beam B. Then, when two signals are contained in the spot S, if the layer N is adjacent to the left part alphaL entirely, a high reflectance ratio is produced against the beam B together with the right part alphaF. If there is any area where the layer N is not adjacent within the part alphaL, the crystal state of this area is changed, the reflectance ratio is decreased and becomes smaller even together with the part alphaF than when the layer N is adjacent to the entire part alphaL. By this difference of the reflectance ratio, only the information of the left part alphaL in the spot S is read out. |
