Multilayer record blank for use in optical recording

Abstract

A flat major surface of a disc-shaped substrate (e.g., of glass) is coated with a light-reflective layer (e.g., of aluminum). Overlying the reflective layer is a layer of material (e.g., fluorescein) which is highly absorptive for light of a frequency supplied by a recording laser. The coating parameters are chosen to establish an anit-reflection condition for the coated record blank at the recording light frequency. The light output of the laser, which is intensity modulated in accordance with a signal to be recorded, is focused upon the coated surface of the disc as the disc is rotated. With the peak intensity of the focused light sufficient to cause ablation of the absorptive layer, an information track is formed as a succession of spaced pits in which the reflecting layer is effectively exposed. For playback, light of a constant intensity is focused on the information track as the disc is rotated. The focused light is of insufficient intensity to effect ablation of the remaining absorptive material, but is of a frequency at which the undisturbed regions of the coated disc exhibit an anti-reflection condition. A photodetector, positioned to receive light reflected from the information track as the pits pass through the path of the focused light, develops a signal representative of the recorded information.