DISK-SHAPED OPTICAL STORAGE MEDIUM AND PROCESS FOR PRODUCING THE SAME

摘要

A disk-shaped optical storage medium for binary information serially stored along a spiral track as pits and lands and readable by means of a laser beam according to the interference principle may be unmistakably marked in a counterfeit-proof manner by designing a selected number among the totality of lands as depressions in the optical reference surface, which are less deep than the pits. This marking, which may take any desired form, may be so small that it can only be made visible by electron microscope means or so large that it can be recognized by the naked eye under a mixed light.