Mathematical modeling of dynamics of fast phase transitions and overheated metastable states during nano- and femtosecond laser treatment of metal targets

• Published in: Mathematical models and computer simulations 2010-06, Vol.2 (3), p.396-405
• Main Authors: Mazhukin, V. I., Mazhukin, A. V., Lobok, M. G.
• Format: Article
• Language: English
• Subjects: Mathematical Modeling and Industrial Mathematics; Mathematics; Mathematics and Statistics; Simulation and Modeling
• ISSN: 2070-0482; 2070-0490
• DOI: 10.1134/S2070048210030130

For a mathematical description of pulsed laser heating, melting, and evaporation of an aluminium target in an ambient atmosphere, a one dimensional, multifront hydrodynamic Stephan problem was used, written for both phases (liquid and solid). On the boundary of solid and gaseous forms, the Stephan problem is combined with radiation gas-dynamic equations, with thermal conductivity, and describes processes in the evaporated material and surrounding gas. For the numerical solution, finite difference method of dynamic adaptation, which gives an opportunity of explicitly tracking interphase boundaries and shock waves, was applied. As a result, in the process of the solution, the problem had 6 computational regions and 7 boundaries, 6 of them were moving, including 2 shock waves and one free boundary in the atmosphere. We used this model to calculate the pulsed laser interaction with an aluminium target with the following parameters: λ = 0.8 μm, τ = 10 −8 –10 −15 s, and G 0 = 10 −9 –10 −16 W/cm 2 . Modeling revealed that in the case of long ∼1 ns pulses, most of the energy is spent on melting and heating the liquid. The depth of the molten pool depth constitutes about 1.2 μm. In the case of femtosecond pulses, most of the energy is spent on heating the solid body and the formation of shock waves in it. The depth of the molten pool does not exceed 0.03 μm. Even though the evaporated layers were of almost the same thickness. For nanosecond laser pulses with fluence J less than 30 J/cm 2 , there is no plasma formation in the evaporated material. For the same fluence of femtosecond laser pulses, plasma is formed after the pulses and is thermal by nature.