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首页> 外文期刊>Mathematical models and computer simulations >Mathematical Modeling of Dynamics of Fast Phase Transitions and Overheated Metastable States During Nanoand Femtosecond Laser Treatment of Metal Targets
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Mathematical Modeling of Dynamics of Fast Phase Transitions and Overheated Metastable States During Nanoand Femtosecond Laser Treatment of Metal Targets

机译：纳米和飞秒激光处理金属靶期间快速相变和过热亚稳态的动力学数学模型

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摘要

Fora 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 = 0.8μm, 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 1.2μm. 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 0.03μm. Even though the evaporated layers were of almost the same thickness. For nanosecond laser pulses with fluence Jless 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.
机译：为了对铝靶材在环境大气中的脉冲激光加热，熔融和蒸发进行数学描述，使用了一维多面流体动力学Stephan问题，针对两个相（液相和固相）进行了描述。在固体和气体形式的边界上，斯蒂芬问题与具有热导率的辐射气体动力学方程相结合，并描述了蒸发物质和周围气体中的过程。对于数值解，应用了动态自适应的有限差分方法，该方法为明确跟踪相间边界和冲击波提供了机会。结果，在求解过程中，问题有6个计算区域和7个边界，其中6个正在移动，包括2个冲击波和1个大气自由边界。我们使用该模型来计算与铝靶的脉冲激光相互作用，其参数如下：λ=0.8μm，τ= 10〜（-8）-10〜（-15）s，G_0 = 10〜（-9） -10〜（-16）w / cm〜2。建模显示，在长-1 ns脉冲的情况下，大部分能量都花在了熔化和加热液体上。熔池深度约为1.2μm。在飞秒脉冲的情况下，大部分能量都花在加热固体上并在其中形成冲击波。熔池深度不超过0.03μm。即使蒸发层具有几乎相同的厚度。对于能量密度小于30 J / cm〜2的纳秒激光脉冲，在蒸发的材料中不会形成等离子体。对于飞秒激光脉冲具有相同的通量，等离子体在脉冲之后形成并且本质上是热的。

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