| 摘要 |
An optical information medium made up of a transparent substrate capable of allowing a recording laser beam to penetrate therethrough; a recording layer formed on the transparent substrate; and a reflective layer formed on the recording layer and reflecting a reproducing laser beam thereupon. A numerical aperture of an objective lens of an optical pickup for irradiating the recording laser beam on the recording layer is approximately 0.65, and the numerical aperture of an objective lens of the optical pickup for irradiating the recording laser beam on the reflection layer is approximately 0.60. An inclination angle theta at both edges of the groove for tracking, being formed spirally on the surface of the transparent substrate on which the recording layer is formed, with respect to the main surface of the transparent substrate, is selected to be from 55° to 75°. An index ∝, expressed by 1-Dr/Ds when assuming that the depth of the groove on the transparent substrate is Ds and the depth of the recording layer at the position of said groove is Dr, is selected to be from 0.2 to 0.4. Further, the full width at half maximum of the groove on the transparent substrate is selected to be from one-third (1/3) to a half (½) of the pitch p of the groove. With this optical information medium, it is possible to record high density signals as signals that are readable optically, as well as to record them with stability.
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