Sandwich holography for storing information interferometrically with a high degree of security.

An entirely new method of storing confidential data is presented. The method is based on sandwich holography, and its-main principle is the following: The basic state of a surface is recorded in one plate of a sandwich pair; in the other plate the same surface is recorded slightly deformed. When the two holograms are combined an interference fringe pattern is formed. By controlling the deformation of the surface it is possible to obtain exactly the interference pattern wainted. This controlled pattern can be used to create information that is either directly readable digital information or a binary coded information, suitable to automatic readout. The data stored in the holograms are not possible to read out from one hologram alone, but the two holograms must be put together to make the information available. The system is primarily meant to be applied on ID cards but can also be used for other applications where data have to be stored securely.