Femtosecond laser irradiation stress induced in pure silica.

We reveal stress fields induced by femtosecond laser irradiation by investigating the topography of surface relaxation of a cleavage of silica plates in which irradiation was performed, varying intensity, laser polarization and displacement of the writing beam. The stress field appears to depend on the writing parameters differently according to the laser intensity. For pulse intensity larger than 0.1 microJ, a first shear stress developed. Above 0.25 microJ, another shear stress appears that is dependent on the direction of writing and coupling with a phase matching condition between the pump wave and the third harmonic.