Laser Heating of Metal Targets Including the Influence of the Background Pressure
Laser Heating of Metal Targets Including the Influence of the Background Pressure
复制标题
金属目标的激光加热，包括背景压力的影响
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
R. Russo
中科院分区：
文献类型：
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作者：
S. H. Jeong;R. Greif;R. Russo
对纳秒脉冲激光加热金属靶在有限压强下的非稳态汽化过程进行了数值研究。采用一维模型对靶加热和蒸汽的气体动力学流动进行了分析，包括对Knudsen层（KL）内蒸汽运动的分析。对于单脉冲激光加热铝靶，发现靶蒸发的阈值激光能量密度很大程度上取决于靶表面的反射率。由热蒸发模型预测的阈值激光能量密度大于实验值。只有当环境压力足够小时，KL边缘处的蒸汽的局部马赫数才在蒸发开始时等于1;对于大的环境压力，蒸汽的马赫数在蒸发的早期阶段首先减小，然后增加到局部声速。在蒸发的早期阶段的气体动力流的加速被发现，并归因于不稳定的绝热膨胀。
Unsteady vaporization of a metal target due to nanosecond pulsed laser heating when an ambient gas of finite pressure exists was studied numerically. A one dimensional model for target heating and for the gasdynamic flow of the vapor was employed including an analysis of the vapor motion inside the Knudsen Layer (KL). For single pulse laser heating of an aluminum target, it was found that the threshold laser fluence for evaporation of the target is greatly dependent upon the target surface reflectivity. The threshold laser fluence predicted by a thermal evaporation model is larger than the values obtained experimentally. The local Mach number of the vapor at the edge of the KL becomes equal to unity at the beginning of evaporation only when the ambient pressure is sufficiently small; for large ambient pressures, the Mach number of the vapor during the early period of evaporation decreases first and then increases to a local sound velocity. An acceleration of the gasdynamic flow during the early period of evaporation was found and attributed to the unsteady adiabatic expansion.