| 摘要 |
PURPOSE:To decrease the distortion of the shape at a converging surface of a conver gent light beam in high-density recording by constituting a medium in such a manner that a phase difference between an ordinary ray and extraordinary ray when these rays are made incident at a specific angle on a transparent resin substrate having specific or lower double refraction satisfies a specific relation. CONSTITUTION:The perpendicular double refraction of the transparent resin substrate of the medium which is provided with a recording layer on the transparent resin substrate and executes recording and reproducing at a track pitch of <1.3mum is specified to <500X10<-6> and the intra-surface double refraction thereof to <20X10<-6>. When the phase difference between the ordinary ray and extraordinary ray when these rays are made incident at an angle + or -theta determined by the numerical aperture of a focusing lens in a direction perpendicular to the substrate from the two directions existing within the plane formed by the main axis of a refractive index ellipsoid A in the thickness direction of the substrate and the axis perpendicular to the substrate plane is defined as R+, R-, R+-R-)/(R++R-)/2<0.04 is satisfied. As a result, the aberrations which are distortions of the shape at the focusing plane are decreased. |
