Optical information medium and recording method therefor

Abstract

An optical information medium, comprising: a transparent substrate for penetrating a recording laser beam therethrough; a recording layer being formed on the transparent substrate; and a reflective layer being formed on the recording layer and for reflecting 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 &thgr; at both edges of the groove for tracking, being formed spiral-like 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 from 55° to 75°. An index &agr;, being expressed by 1−Dr/Ds when assuming that depth of the groove on the transparent substrate is Ds and depth of the recording layer at position of said groove is Dr, is selected from 0.2 to 0.4. Further, full width at half maximum of the groove on the transparent substrate is selected to be from one-third (⅓) 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 being readable optically, as well as to record them with stability.