High refractive index modification of SiO2 created by femtosecond laser nanostructuring

By comparing simulations with experiment, we show that the effective refractive index of fused SiO2 can be locally reduced by (1.8 +/- 0.2)% by femtosecond laser nanostructuring. We create a microlens of material containing a planar array of nanocracks embedded inside fused silica and probe how it refracts or absorbs light as a function of pulse energy. The self-generated microlens lowers the peak light intensity by deflecting the light around the focus. We obtain the refractive index by simulating the beam transport using the 3D wave equation in conjunction with the measured dimensions of the modified material.