Patent ID: 8111441

Claim:
Method for treating a nominally pure crystal having non-linear optical properties, the nominally pure crystal containing foreign atoms at a residual concentration of less than 20 ppm so as to provide specific absorption of incident light, the method comprising: determining, based on testing on a specifically doped reference crystal of same type as the nominally pure crystal, a threshold value defined by a temperature at which a migration of ions in the nominally pure crystal to the surface of the nominally pure crystal ceases; transforming the foreign atoms 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 2.5° C. per minute to a maximum temperature above the threshold value and below a Curie temperature of the nominally pure crystal; and applying an electrical voltage so as to eliminate electrons released during the oxidation process from the nominally pure crystal.