Photoionization of silicate glasses exposed to IR femtosecond pulses

Photoionization of alkali-silicate. bore-silicate, lead-silicate and photosensitive multi-component silicate glasses has been studied under exposure to infrared femtosecond laser pulses at irradiance below the thresholds of laser-induced damage and catastrophic self-focusing. It is proved that the supercontinuum that is generated in all glasses studied as a result of the femtosecond laser pulses spectral broadening extends up to the short-wavelength part of the ultraviolet region of spectrum even if the glass is opaque in this region. It is shown that photoionization results from absorption of the short-wavelength component of this supercontinuum generated by infrared radiation. This ionization leads to the color center formation and luminescence in the bulk of glasses studied. Photoionization of photosensitive multicomponent glasses leads to the creation of latent image and to the refractive index changing in exposed area after thermodevelopment. Fused silica exhibits the same spectral broadening too but color center formation in the visible was not recorded at irradiance up to the laser damage threshold. (C) 1999 Elsevier Science B.V. All rights reserved.