Optical switch, especially for information storage and retrieval

摘要

Nitroprusside single crystals having the formula Mn[Fe(CN)5]nH2O, where M is a metal that forms a nitroprusside is found to have the property, when cooled to a temperature in the range between 160 DEG K. and 250 DEG K., of convertability into a long-duration metastable state by irradiation with coherent blue-green light and to return to the original state when irradiated with red light. Barium nitroprusside Ba[Fe(CN)5]2H2O can be switched rapidly from one state to the other without requiring cooling below about 200 DEG K. and lends itself particularly well to making single crystal memories for writing with a blue-green laser beam and reading with a red laser beam, with the readout being picked up by a photodetector diode array, on which the radiation from the nitroprusside crystal is focused. The incident laser beams are pulsed and the photodetector is turned off during pulsing. Movable laser mirrors are used to direct the laser beams to locations on the surface of the crystal in a manner controlled by an address program.