| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical disk which is capable of attaining the compatibility of the assurance of an alteration prevention function of information with the assurance of excellent recording characteristics. SOLUTION: After the information is recorded on the recording layer 14, a light transparent layer 16 is thermally shrunk by a heat treatment, thereby, its thickness is reduced from D1 to D2 (D2<D1). When the optical disk is irradiated with a laser beam L, the optical path length of the laser beam L transmitted through the light transparent layer 16 is made shorter than that in the state before the heat treatment process step and an optical aberration is generated. The diameter of the irradiation spot of the laser beam L to the recording layer 14 is made into W2 (W2>W1) greater than the diameter W1 of the irradiation spot before the heat treatment by this optical aberration, by which the resolution of the laser beam L is lowered. Only the reproduction of the information recorded in the recording layer 14 is made possible and the rewriting of the information is made infeasible. |
