Information medium adapted to be written by thermo-optical means and

Abstract

An information medium adapted to be written by thermo-optical means comprising a heat-sensitive structure adapted to store information to be read by optical means. This includes a thin metal layer, which, when incident writing radiation impinges on it, causes a transient localized temperature rise. Above a temperature threshold this causes a change in the optical characteristics of the heat-sensitive structure. The information medium is manufactured by a method involving depositing a continuous thin film of polycrystalline aggregate over an acceptor surface of the aforementioned structure by means of an incident flux of particles of a precious metal and a transition metal. In order to obtain a defined metallic composition, these metal particles are extracted from at least one target exposed to bombardment by other particles resulting from an electrical discharge in a rare gas at reduced pressure and confined by a magnetic field. The acceptor surface collects these metal particles with a residual energy content giving rise to a density of nucleation sites increased relative to that for a similar deposit obtained by vacuum evaporation. The maximum distance between the target and the acceptor surface is preferably not more than twenty centimeters, and advantageously not more than ten centimeters.