Multi-parametric study of ultrashort pulse laser irradiation of glass surfaces: impact of air photo-ionization

A multi-parametric study of ultrashort-pulse laser irradiation of glass materials has been performed in the regimes of surface ablation/modification. A concept is verified that the ultraclean laser ablation can be achieved at a certain window of the process parameters, which depends on material properties such as band gap and the softening temperature. Single- and multi-shot laser ablation of fused silica and Willow glass, which have different thermophysical and optical properties, was carried out by Ti:sapphire laser delivering 130 fs pulses at wavelength of 800 nm. Special attention is paid to the role of laser-induced ionization of ambient air in high-precision surface processing. A range of techniques such as optical profilometry, scanning electron microscopy, and space-and-time resolved spectroscopy were used to study crater profiles and quality as well as optical emission from laser ablated material and air plasma excited in front of the irradiation spot. The evolution of emission spectra is analyzed as a function of pulse energy and repetition rate. The excitation levels and glass temperature were evaluated by modeling based on the rate and energy equations.