The polarization-dependence of femtosecond laser damage threshold inside fused silica

The laser damage threshold inside fused silica is dependent not only on the numerical aperture (NA) of the focusing objective, but also on the polarization of the incident femtosecond laser pulses. The damage threshold for circularly polarized beams is higher than that for linearly polarized beams when NA > 0.4, but the former was lower than the latter when NA < 0.4. The reverse might be due to different damage processes: laser induced damage at high NA and the self-focusing induced breakdown at low NA.