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We report photoluminescence in bulk chloride photo-thermo-refractive glass under irradiation with femtosecond laser pulses. The fluorescence originates from the bleaching of silver nanoparticles precipitating in the glass. Similarly to the conventional process of the femtosecond re-shaping of metal inclusions with diameter tens of nanometers, irradiation of the smaller nanoparticles results in a fast shrinking size with an ellipsoidal shape via photofragmentation. Under UV excitation, remaining sub-nanometer silver molecular clusters show visible and near IR fluorescence, which increases with chlorine concentration. The observed bleaching of silver nanoparticles in bulk glass-metal nanocomposite can find applications in data storage and bleaching of volume Bragg gratings.

We report on the optical properties of volume Bragg gratings in chloride photo-thermorefractive glass after femtosecond laser bleaching. We show experimentally that irradiation of the gratings with femtosecond laser pulses can expand their transmission into the whole visible range without dramatic decrease of diffraction efficiency. The mechanism of glass bleaching is considered and modulation of refractive index is described in terms of the coupled wave theory for mixed volume Bragg gratings.

We demonstrate that the Joule heating of the volume Bragg grating recorded in chloride photo-thermo-refractive glass can be suppressed by bleaching the silver nanoparticles with intense ultrashort laser pulses. Measurement of the bleached grating angular selectivity showed that, at the signal wavelength at 972 nm, the spectral drift is 0.5 nm at the CW laser diode beam intensity as high as 145  W/cm. Thus, the bleaching of silver nanoparticles results in the improved thermal stability of transmission gratings, allowing one to employ them to control the powerful CW laser radiation.

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