Permanent photoreduction of Sm3+ to Sm2+ inside a sodium aluminoborate glass by an infrared femtosecond pulsed laser

We report the observation of permanent photoreduction of Sm3+ to Sm2+ inside a transparent and colorless Sm3+-doped sodium aluminoborate glass. After irradiation by an 800 nm focused femtosecond pulsed laser, the focused part of the laser in the glass became orange. Absorption and photoluminescence spectra showed that a part of Sm3+ was reduced to Sm2+ after the laser irradiation. Electron spin resonance spectra of the glass before and after the laser irradiation were also measured. The observed phenomenon is inferred to be useful for the fabrication of optical memory devices with an ultrahigh storage density. (C) 1999 American Institute of Physics. [S0003-6951(99)02501-2].