Femtosecond laser-shockwave induced densification in fused silica

A tightly focused femtosecond laser-beam in the non-ablative regime can induce a shockwave sufficiently intense to reach local pressures in the giga-Pascal range or more. In a single beam configuration, the location of the highest-pressure zone is nested within the laser-focus zone, making it difficult to differentiate the effect of the shockwave pressure from photo-induced and plasma relaxation effects. To circumvent this difficulty, we consider two spatially separated focused beams individually acting as quasi-simultaneous pressure-wave emitters. The zone in between the two laser beams where both shockwaves superpose forms a region of extreme pressure range, physically separated from the regions where the plasma formed. Here, we present a detailed material investigation of pressured-induced densification in fused silica occurring in between the foci of two laser beams. The method used is generic and can be implemented in a variety of transparent substrates for high-pressure physics studies. Unlike classical methods, such as the use of diamond anvils, it potentially offers a means to create arbitrary patterns of laser-induced high-pressure impacted zones by scanning the two beams across the specimen volume.