Patent US 3,944,978

A reference diffraction pattern is generated by radiating an invariant physical characteristic such as a fingerprint with coherent light, this reference diffraction pattern being converted by a detector into a reference electrical function which is stored. A person to be identified then has a corresponding invariant physical characteristic such as his fingerprint radiated by coherent light to cause generation of a sample diffraction pattern. The frequency domain of the entire sample diffraction pattern is detected simultaneously to provide a sample electrical function. The reference electrical function in storage is then compared with the sample electrical function and if a correlation exists within a given tolerance, it is known that the person from which the sample electrical function is derived corresponds to the person from which the reference electrical function was derived. The invariant physical characteristics may be fingerprints as mentioned, or signatures, or combinations of both.