Abstract: Method for treating a nominally pure crystal having non-linear optical properties. The nominally pure crystal contain foreign atoms at a residual concentration of less than 20 ppm so as to provide specific absorption of incident light. The method includes determining, based on testing on a specifically doped reference crystal of same type as the nominally pure crystal, a threshold value. The threshold value is defined by a temperature at which a migration of ions in the nominally pure crystal to the surface of the nominally pure crystal ceases. The foreign atoms are transformed to a higher valance state by a thermally-supported oxidation process including heating the nominally pure crystal at a heating rate that increases by less than 3 ° C. per minute to a maximum temperature above the threshold value and below a Curie temperature of the nominally pure crystal. An electrical voltage is applied so as to eliminate electrons released during the oxidation process from the nominally pure crystal.

Abstract: Method for treating a nominally pure crystal having non-linear optical properties. The nominally pure crystal contain foreign atoms at a residual concentration of less than 20 ppm so as to provide specific absorption of incident light. The method includes determining, based on testing on a specifically doped reference crystal of same type as the nominally pure crystal, a threshold value. The threshold value is defined by a temperature at which a migration of ions in the nominally pure crystal to the surface of the nominally pure crystal ceases. The foreign atoms are transformed to a higher valance state by a thermally-supported oxidation process including heating the nominally pure crystal at a heating rate that increases by less than 3° C. per minute to a maximum temperature above the threshold value and below a Curie temperature of the nominally pure crystal. An electrical voltage is applied so as to eliminate electrons released during the oxidation process from the nominally pure crystal.

Abstract: A magnetic storage medium is read by incident polarized light and reflected outgoing light defining a common plane. The polarized incident light preferably has a polarization vector at 40.degree. to 50.degree. to this plane and at the storage medium, the magnetization is in a direction perpendicular to the plane. The preamplified output signal V.sub.M from the photodiode transducing the outgoing light beam has a fixed value V.sub.O subtracted therefrom where V.sub.O is a function of the sensitivity and resolving power of the electronic circuitry. The signal V.sub.M -V.sub.O is then amplified and processed to represent the stored data.

Abstract: Nitroprusside single crystals having the formula M.sub.n [Fe(CN).sub.5 ]nH.sub.2 O, 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.degree. K. and 250.degree. 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).sub.5 ]2H.sub.2 O can be switched rapidly from one state to the other without requiring cooling below about 200.degree. 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.