Optical data storage based on the long-lived photon echo

The phenomenon of the long-lived photon echo (LPE), discovered in a previous paper can be used for optical storage. We discuss the main peculiarities of LPE in a three-level system, one level of which is metastable. The crystals, doped by the rare-earth ions such as Pr/sup 3+/ and Eu/sup 3+/, the Van Vleck paramagnetics, are usually used as the data medium of such optical storage.