Dobbeltstablet optisk datalagermedie og anvendelse af et sådan medie

摘要

A dual-stack optical data storage medium (20) is described for read out using a focused radiation beam (29) with a wavelength of 400 - 410 nm and a Numerical Aperture (NA) of 0.84 - 0.86. The medium has a substrate (21) and a first stack of layers named L0 (22) comprising a first information layer and a second stack of layers named L1 (23), comprising a second information layer. A radiation beam (29) transparent spacer layer (24) is present between L0 and L1. A transmission stack named TS0 with a thickness d TS0 and an effective refractive index n TS0 contains all layers between L0 and an entrance face (26) of the medium (20). A transmission stack named TS1 with a thickness d TS1 and an effective refractive index n TS1 containing all layers between L1 and the entrance face (26). The spacer layer (24) has a thickness selected from the range 20 - 30 µm, the thickness D TS0 in dependence on the refractive index n TS0 and the thickness D TS1 in dependence on the refractive index n TS0 are within a specified area. In this way a reliable read out of both the first and the second information layer of respectively L0 and L1 is achieved.