Irradiation of glass with infrared femtosecond laser pulses

Femtosecond laser pulses can be absorbed by materials with larger energy band gap than the single photon energy through non-linear processes occurring in very small volumes. Thus, femtosecond lasers are exceptional tools for the modification of these materials with high resolution. This work is focused in the study of craters produced on the surface of a soda-lime glass after irradiation with a laser delivering 450 fs pulses at 1027-nm wavelength. The ablation with different energies and number of pulses is analyzed. Scanning electron microscopy and confocal microscopy are used to characterize the morphology of the ablation craters. The results show that micrometric resolution can be achieved with a focusing lens of 0.25 NA and pulse energies of few microjoules. The dependence of the laser fluence threshold on the number of pulses reveals the existence of an incubation effect. The trend for low number of pulses suggests a 4-photon ionization process.