Intrinsic single- and multiple-pulse laser-induced damage in silicate glasses in the femtosecond-to-nanosecond region

We show that the threshold power density of the intrinsic laser-induced damage in borosilicate glass at similar to1 mum wavelength does not depend on pulse duration from 2x10(-13) to 3x10(-8) s and has the same value for both single- and multiple-pulse exposure of the sample. This indicates that the mechanism of the intrinsic damage in glasses involves a collective response of a certain volume in the dielectric as a whole, such as "dielectric-metal" phase transition, rather than a process of individual generation and accumulation of electrons, such as multiphoton, tunneling, or avalanche. Also, we demonstrate that under femtosecond exposure the threshold of the plasma formation in transparent glasses is considerably higher than the threshold of the residual change of medium parameters.