Fused silica ablation by double femtosecond laser pulses: influence of polarization state

Glass processing is a subject of high interest for many industrial fields such as optics manufacturing, smart electronics or medical devices. With respect to nanosecond technology, the use of femtosecond lasers allows to achieve high processing quality thanks to nonlinear absorption properties. Nevertheless, the throughput of femtosecond processing is still very low when compared to other laser technologies. Temporal and spatial pulse shaping is a smart and flexible solution to further increase the efficiency of femtosecond laser processing by driving efficiently both electron dynamics and absorption involved during laser irradiation. In the present work, the effect of temporal pulse shaping on fused silica ablation is investigated by single-wavelength (1030nm) double femtosecond pulses pump-pump experiment. Two sub-pulses are focused on the top surface of fused silica with two different polarization configurations: (i) orthogonally-crossed linear polarization or (ii) counter-rotating circular polarization. The investigated parameters are the pulse-to-pulse delay, set with a delay line, the total fluence and the polarization configuration. The results are discussed in term of optical transmission, modification and ablation thresholds, and ablated volume. A numerical model describing the electron dynamics and the absorbed energy density is also presented to support interpretation of experimental results. It is demonstrated that pulse-to-pulse delay has a major influence on ablated volume, modification and ablation threshold. Polarization state has also, to a lesser extent, a significant influence on ablated volume. Their cooperative effect on the ablation efficiency is discussed. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement