sentences:  In the 1970s, Valeri Barachevskii demonstrated that this photochromism could be produced by two–photon excitation, and finally at the end of the 1980s Peter M. Rentzepis showed that this could lead to three-dimensional data storage.Most of the developed systems are based to some extent on the original ideas of Rentzepis.A wide range of physical phenomena for data reading and recording have been investigated, large numbers of chemical systems for the medium have been developed and evaluated, and extensive work has been carried out in solving the problems associated with the optical systems required for the reading and recording of data.