Irradiation of solids with subpicosecond laser pulses: excitation and relaxation dynamics of electrons and phonons

Baerbel Rethfeld; Andreas Kaiser; Martin Vicanek; Gerhard Simon

doi:10.1117/12.321574

14 September 1998 Irradiation of solids with subpicosecond laser pulses: excitation and relaxation dynamics of electrons and phonons

Baerbel Rethfeld, Andreas Kaiser, Martin Vicanek, Gerhard Simon

Author Affiliations +

Proceedings Volume 3343, High-Power Laser Ablation; (1998) https://doi.org/10.1117/12.321574
Event: High-Power Laser Ablation, 1998, Santa Fe, NM, United States

Abstract

Irradiation of metals and dielectrics with subpicosecond laser pulses reveals a variety of different microscopic processes compared to longer pulses. We choose a transport theoretical description of electrons and phonons, which allows us to investigate the contribution of particular collision processes on macroscopic material response, even for highly nonequilibrium subsystems where a hydrodynamic description fails. The absorption of laser energy is described by photon- absorption of free electrons with assistance of phonon collisions. We considered relaxation of the electron gas by electron-electron and electron-phonon collisions. In the case of a dielectric, terms for multiphoton ionization and impact ionization are included. A resulting system of coupled time- dependent Boltzmann equations is solved numerically. For SiO₂ as an example of dielectrics we calculate changes in occupation numbers of electrons and phonons, respectively, determining the sequence of excitation and relaxation of the subsystems under ultrashort laser pulse irradiation. It is shown that the essential process of free-electron generation is multiphoton ionization. Additionally, we investigate polarization effects for the case of irradiation of metals. Using parameters for gold we find anisotropic absorption of laser energy, which depends on polarization of the electric field and material parameters as well as on photon energy of irradiating laser light.

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Baerbel Rethfeld, Andreas Kaiser, Martin Vicanek, and Gerhard Simon "Irradiation of solids with subpicosecond laser pulses: excitation and relaxation dynamics of electrons and phonons", Proc. SPIE 3343, High-Power Laser Ablation, (14 September 1998); https://doi.org/10.1117/12.321574

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