Confocal fluorescence and Raman microscopy of femtosecond laser-modified fused silica

Modified lines were written inside Corning 7940 fused silica with 130 fs laser pulses from an amplified Ti-sapphire laser operating at 800 nm at a repetition rate of 1 kHz. The sample was scanned at 20 μm s^-1 with laser pulse energies ranging from 1 to 35 μJ, resulting in modified lines with diameters ranging from 8 to 40 μm. Confocal fluorescence and Raman microscopy was used to probe for spatial variations in defect concentration and glass structure across the modified lines. The fluorescence intensity decreased with increasing distance from the line centre, whereas the Raman intensity increased. No significant variations in the concentration of three- and four-membered ring structures were observed.