Pulsed laser-induced ablation of absorbing liquids and acoustic-transient generation
Pulsed laser-induced ablation of absorbing liquids and acoustic-transient generation
复制标题
脉冲激光诱导吸收液体烧蚀和声瞬变产生
DOI：
--
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
C. Grigoropoulos
中科院分区：
文献类型：
--
作者：
Dongsik Kim;M. Ye;C. Grigoropoulos
2CrO 4用KrF准分子激光（λ=248 nm，FWHM=24 ns）以低于等离子体形成阈值的中等能量密度（高达100 MW/cm 2）辐照。烧蚀过程，包括蒸汽空腔的形成和声波的传播是可视化的激光闪光摄影。消融阈值是通过测量产生的压力瞬变和气相动力学使用宽带压电压力传感器和同时光传输探头，分别确定。基于液体介质的热弹性行为和蒸发动力学，研究了液体烧蚀和声脉冲产生的机理。提出了一个描述高激光注量下爆炸汽化过程的数值模型。计算结果与实验结果进行了比较，在短脉冲加热条件下，在不显著提高液体温度的情况下，热弹性应力的拉伸分量可以在较低的激光能量密度下引发烧蚀。另一方面，如果加热速率足够快以实现液体的高度过热，则气泡成核速率的突然增加导致爆炸性蒸发，这在烧蚀动力学中起主要作用。在液体中的压力瞬变产生热弹性在低的激光能量密度，但汽相膨胀和/或由烧蚀羽流施加的反冲动量的贡献变得显着在高的激光能量密度。在爆炸性蒸发的情况下，在环境空气中形成冲击波。这些波阵面的传播与数值计算结果吻合得很好。
2CrO4 are irradiated by a KrF excimer laser (λ=248 nm, FWHM=24 ns) with moderate energy density (up to 100 MW/cm2) below the plasma-formation threshold. The ablation process, including the vapor-cavity formation and the acoustic-wave propagation is visualized by laser-flash photography. The ablation thresholds are determined by measuring the generated pressure transients and vapor-phase kinetics using a broadband piezoelectric pressure transducer and a simultaneous optical-transmission probe, respectively. The mechanisms of liquid ablation and acoustic-pulse generation are investigated based on the thermoelastic behavior of the liquid medium and the evaporation dynamics. A numerical model is proposed to describe the explosive-vaporization process at high laser fluences. The computation results are compared with the experiment.In short-pulse heating, ablation can be initiated at low laser fluences by the tensile component of the thermoelastic stress without a significant increase in the liquid temperature. On the other hand, if the heating rate is rapid enough to achieve a high degree of superheating of the liquid, the abrupt increase of the homogeneous-bubble-nucleation rate leads to explosive vaporization, which then plays the major role in the ablation dynamics. The pressure transient in the liquid is generated thermoelastically at low laser fluences, but the contribution of the vapor-phase expansion and/or the recoil momentum exerted by the ablation plume becomes significant at high laser fluences. Shock waves are formed in the ambient air in the case of explosive vaporization. The propagation of these wave fronts is in good agreement with the numerical-computation results.