Polarization dependence of refractive-index change in silica glass induced by self-trapped filament of femtosecond laser pulses

Abstract

We have already shown that the refractive-index change is induced by a self-trapped filament of ultrashort laser pulses in silica glass. In this paper, we investigate the dependence of refractive-index change on polarization of incident laser pulses in silica glass. In the experiment, we focused linearly polarized pulses inside a sample of silica glass. We polished the sample and etched by 5% HF solution to observe the cross-sectional view of the regions of refractive-index change that are perpendicular to the filament. The observation with a scanning-electron microscope shows that the cross-section is elliptical and the long axis was parallel to polarization direction of incident laser pulses. The ellipticity was 0.85. We fabricated gratings to estimate the index ellipsoid of the region of refractive-index change. We confirmed that the index ellipsoid was uniaxial and negative. The optic axis was parallel to the axis of the filament and the birefringence was 1×10 -3 .