Densification of silica glass induced by 0.8 and 1.5μm intense femtosecond laser pulses

We investigate the physical mechanisms responsible for waveguide formation in silica glass induced by 1kHz intense femtosecond laser pulses from a Ti-sapphire laser at 0.8μm as well as from a femtosecond optical parametric amplifier at 1.5μm. It is demonstrated that the densification taking place at the irradiated region is the principal cause for refractive index change in the waveguides written with both 0.8 and 1.5μm pulses. The birefringence induced by the stress arising from such densification and its behavior against thermal annealing are also studied.