Abstract: To obtain a higher recording density, and thus higher data capacity, it is proposed according to the present invention to reduce the numerical aperture of the optical means (3, 4) in the direction orthogonal to the information recording direction, which is the radial direction for an optical disc, during recording of information to obtain a light beam having a substantially oval spot profile having a shorter axis in the information recording direction, i.e. the tangential direction for an optical disc, compared to the direction orthogonal that to, i.e. the radial direction. Recording marks having a corresponding oval profile arec achieved.

Abstract: An optical data storage medium (20) for recording by means of a focused radiation beam (29) is described. The radiation beam having a wavelength ? enters through an entrance face (28) of the medium during recording. The medium has a substrate (21) with a surface (24) including a guide groove with a depth g. An inverted stack of layers is present on the substrate (21) including a reflective layer (24a) with a complex refractive index ñM?=nM??i*kM?, in substantial conformity with the surface (24) of the substrate, a transparent layer (22) through which the radiation beam (29) is incident with a complex refractive index ñT?=nT??i*kT? and a recording layer (25) of a material having a complex refractive index ñR?=nR??i*kR? and having a thickness dRG in the groove portion and a thickness dRL in the portion between grooves. The recording layer is interposed between the reflective layer (24a) and the transparent layer (22). When 0.25/(3.0+kM?2)+0.17<g*nT/?<0.22/(3.0+kM?2)+0.45 and 0.2<(dRG?dRL)/g<0.