Patent ID: 7221642

Claim:
An optical data storage medium for recording by means of a focused radiation beam having a wavelength λ and entering through an entrance face of the medium during recording, at least comprising: a substrate, with a surface including a guide groove with a depth g, a stack of layers on the substrate, which stack includes: a reflective layer of a material having a complex refractive index ñ Mλ =n Mλ −i*k Mλ at the wavelength λ, n M denoting the real part and k M denoting the imaginary part of ñ Tλ , present adjacent the surface of the substrate in substantial conformity with the surface, a transparent layer through which the radiation beam is incident during recording and of a material having a complex refractive index ñ Tλ =n Tλ −i*k Tλ , a recording layer of a material having a complex refractive index ñ Rλ =n Tλ −i*k Rλ and having a thickness d RG in the groove portion and a thickness d RL in the portion between grooves, being interposed between the reflective layer and the transparent layer, characterized in that the following requirements are fulfilled: 0.25/(3.0+ k Mλ 2 )+0.17 <g*n T /λ<0.22/(3.0 +k Mλ 2 )+0.45 and 0.2<(d RG −d RL ) g< 0.5 and 0 <d RG <λ/n Rλ and k Rλ <0.5 and 2<n Rλ <2.6.