Investigations on laser damage growth in fused silica with simultaneous wavelength irradiation.

The laser-induced damage growth phenomenon is experimentally studied for damage sites on the exit surface of fused silica. The sites are irradiated by nanosecond laser pulses at 1064 and 355 nm separately and also simultaneously. The results in the single wavelength configurations are expressed in terms of the probability of growth and growth coefficient. For growing sites, a fluence correction expression is proposed in order to take into account the millimetric Gaussian profile of the beams. The use of this expression is necessary to obtain results that are consistent with the ones obtained in the existing literature with large homogeneous beams. In the multiple wavelengths configuration, the results are expressed as a function of the laser fluences at each wavelength and are found to be closely related to the parameters determined in the single wavelength experiments. A coupling between the two wavelengths is quantified, and could originate from the formation and the expansion of a plasma produced both in the center and at the periphery of the damage sites.