Investigation of ultrashort laser excitation of aluminum and tungsten by reflectivity measurements
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S.I. : CURRENT STATE-OF-THE-ART IN LASER ABLATION
Investigation of ultrashort laser excitation of aluminum and tungsten by reflectivity measurements T. Genieys1 · M. Sentis1 · O. Utéza1 Received: 14 October 2019 / Accepted: 3 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We determine the laser-induced ablation threshold fluence in air of aluminum and tungsten excited by single near-infrared laser pulses with duration ranging from 15 to 100 fs. The ablation threshold fluence is shown to be constant for both metals, extending the corresponding scaling metrics to few-optical-cycle laser pulses. Meanwhile, the reflectivity is measured providing access to the deposited energy in the studied materials on a wide range of pulse durations and incident fluences below and above the ablation threshold. A simulation approach, based on the two-temperature model and the Drude–Lorentz model, is developed to describe the evolution of the transient thermodynamic and optical characteristics of the solids (lattice and electronic temperatures, reflectivity) following laser excitation. The confrontation between experimental results and simulations highlights the importance of considering a detailed description and evolution of the density of states in transition metals like tungsten. Keywords Ultrashort pulses · Ablation · Reflectivity · Metals · Tungsten · Femtosecond
1 Introduction Femtosecond lasers have the ability to machine materials with good efficiency, minimized thermal budget and collateral effects [1, 2]. Nevertheless, the evaluation of observables to benchmark matter transformation is still scarce in the ultrashort regime (≪ 100 fs) providing evident interest to this ongoing research. For instance, no determination of single-shot laserinduced ablation threshold fluence (Fth) can be found for most metals, including tungsten or aluminum studied here, at pulse durations as short as 15 fs. Measurements can be found at longer femtosecond pulse duration, most commonly in multipulse regime with the objective of surface structuration of metallic materials and enhancement of their surface properties for various scientific and industrial applications [3, 4]. Moreover, the development of predictive quantitative models for the description of the interaction is of great interest whether for a best control of material modification or to estimate the resistance of a given material to laser irradiation. The most widely employed is the two-temperature model * T. Genieys [email protected]‑mrs.fr 1
Aix-Marseille University, CNRS, LP3 UMR 7341, 13288 Marseille, France
(TTM) [5] which calculates the temporal and spatial evolution of the temperature of electron and ion subsystems following laser excitation. Improvement of modeling accuracy involves understanding complex phenomena at different timescales, from femtoseconds to nanoseconds. They include laser heating of the electrons and electron–electron energy exchange at the pulse timescale followed by progressive energy transfer to the lattice. In mos
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