OPTICAL DATA STORAGE MEDIUM AND USE OF SUCH MEDIUM

摘要

An optical data storage medium (10) is described for read out using a focused radiation beam (19) with a wavelength lambda and a Numerical Aperture NA. The medium has a substrate (11) and a first stack of layers named L0 (12) comprising a first information layer and optionally at least one further stack of layers named Ln (13), comprising a further information layer. A radiation beam (19) transparent spacer layer (14) is present between each of L0 and Ln. A transmission stack named TS0 with a thickness dTS0 contains all layers between L0 (12) and an entrance face (16) of the medium (10). A transmission stack named TSn with a thickness dTSn contains all layers between Ln (13) and the entrance face (16). The maximum deviation of dTS0 and when applicable dTSn does not exceed a predetermined value DEVdTS0 or DEVdTSn, measured over the information area of the medium (10) and this value is set in dependency of lambda and NA. In this way a reliable read out of the information layer(s) without the need for dynamic spherical aberration correction is achieved.