Nanospallation induced by a femtosecond laser pulse

M. B. Agranat; S. I. Anisimov; S. I. Ashitkov; V. V. Zhakhovskii; N. A. Inogamov; K. Nishihara; Yu. V. Petrov

doi:10.1117/12.738550

18 December 2007 Nanospallation induced by a femtosecond laser pulse

M. B. Agranat, S. I. Anisimov, S. I. Ashitkov, V. V. Zhakhovskii, N. A. Inogamov, K. Nishihara, Yu. V. Petrov

Proceedings Volume 6720, Laser-Induced Damage in Optical Materials: 2007; 672002 (2007) https://doi.org/10.1117/12.738550
Event: Boulder Damage Symposium XXXIX: Annual Symposium on Optical Materials for High Power Lasers, 2007, Boulder, Colorado, United States

Abstract

In the present work phenomena are considered related to the interaction of ultra-short laser pulses, τ_L~0.1 ps, with metallic targets. The absorption of laser pulse results in formation of thin layer of hot electrons strongly superheated (T_e>>T_i) relative to the ion temperature, T_i. Initial thickness of the layer d_heat is small, d_heat~δ, where δ~10 nm is the skin layer thickness. Subsequent developments include the following stages: (1) Propagation of electron thermal wave which expands the hot layer d_heat; (2) Cooling of electrons due to energy transfer to cold ions; (3) Onset of hydrodynamic motion that constitutes the rarefaction wave with positive pressure; (4) Further expansion of target material leading to the appearance of negative pressure; and (5) Long separation process which begins with nucleation of voids and goes on to the total separation of spallation plate. The thickness of the plate is ~10 nm (we call it nanospallation). Theoretical model involves two-temperature hydrodynamic equations with semiempirical EOS for a metal, electron heat conduction and electron-ion energy exchange. The decay of metastable strongly stretched matter is described by molecular dynamics (MD) simulation with extremely large number of atoms. The experimental setup includes femtosecond chromium-forsterite laser operating in the pump-probe regime. The experiments are performed with gold target. Measured ablation threshold for gold is 1.35 J/cm² of incident pump light at inclination 45°, p-polarization. Calorimeter measurements give for the absorbed fluence F_abs=0.3F_inc, therefore the threshold value of F_abs is 0.4 J/cm².

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M. B. Agranat, S. I. Anisimov, S. I. Ashitkov, V. V. Zhakhovskii, N. A. Inogamov, K. Nishihara, and Yu. V. Petrov "Nanospallation induced by a femtosecond laser pulse", Proc. SPIE 6720, Laser-Induced Damage in Optical Materials: 2007, 672002 (18 December 2007); https://doi.org/10.1117/12.738550

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