CC BY
25LMI-O-4
Dynamic optical response of gold to ultrafast laser action: modeling of damage threshold and comparison with experiment
S.A. Lizunov12,1. Mirza1, M. Stehlik1, N.M. Bulgakova1,2, A.V. Bulgakov12
1HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech
Republic
2S.S. Kutateladze Institute of Thermophysics, Siberian Branch of RAS, Novosibirsk, Russian Federation
Ultrashort (femtosecond and picosecond) lasers have proven to be a great tool for processing of any kind of materials. Due to minimized heat diffusion effects during the action of such pulses, it is possible to create nanosized surface modifications with higher accuracy and smaller energy input as compared to nanosecond and longer pulses. However, because of complexity and multiplicity of the processes triggered in materials by the laser action, the laser-matter interaction phenomenon as a whole and contributions of individual processes to material response on laser light remain challenging. Further advances of ultrafast laser processing demand further thorough studies using both theoretical and experimental approaches and comparison between them.
The optical response of metal surfaces to high-power laser excitation is one of the important topics of laser-matter interaction. As was shown in our recent studies [1], it swiftly changes during laser pulse action and strongly depends on the amount of absorbed energy, which in its turn depends on the optical response. Such interrelation is very complex and cannot be understood based on available experimental techniques. A combination of numerical simulation and experimental probing of laser-induced processes performed for the same irradiation conditions is likely to be the most efficient way of gaining deep insights into the rapid structural and phase transformations of materials triggered by ultrashort laser pulses. Many numerical models have been proposed with different estimations of optical and thermophysical parameters. However, all these models give satisfactory agreement with measurements only for limited ranges of applied laser fluences that calls for further studies.
In this work, results of numerical simulations of ultrashort laser irradiation of gold are reported for a wavelength of 800 nm at a pulse duration of 124 fs and a wavelength 1030 nm at pulse durations of 260 fs and 7 ps. The core of the model is the two-temperature approach supplemented with models of optical response. Several optical models were tested in the simulations. The dynamic changes of thermophysical parameters of gold (both for electronic and lattice subsystems) were taken into account, based on existing literature data. For every optical model and every set of thermophysical properties, the melting threshold fluences were calculated and compared with the experiments. Based on the comparison, the roles of the electron-phonon coupling factor and ballistic electrons will be discussed.
References
[1] M.V. Shugaev, M. He, S.A. Lizunov, Y. Levy, T. J.-Y. Derrien, V P. Zhukov, N.M. Bulgakova, L.V. Zhigilei, Insights into Laser-Materials Interaction Through Modeling on Atomic and Macroscopic Scales, In: Advances in the Application of Lasers in Materials Science, Springer Series in Materials Science, Ed. P.M. Ossi, Vol. 274, Chapter 5 (Springer, 2018). - P. 107-148.
