Comparative study of UV absorption changes induced in germanosilicate glass by high-intensity femtosecond pulses at 267, 400 and 800 nm

We investigated UV absorption changes induced in 3.5 mol% Ge-doped fused silica at high-intensity (∼10¹¹-10¹³ W/cm²) femtosecond (130 fs) irradiation at 267, 400 and 800 nm. We have shown that the induced spectra in the region 190-300 nm are similar in all three cases. At 800 nm irradiation, in addition to the UV absorption changes, we observed small-scale damage due to self-focusing. This damage appears when the incident pulse fluence value of about 1 J/cm² (pulse intensity of about 7.5 × 10¹² W/cm²) is overcome, while the threshold for the induced absorption changes is twice lower.