短强脉冲VUV辐照下原子团簇的电离和膨胀动力学
Ionization and expansion dynamics of atomic clusters irradiated with short intense VUV pulses
摘要：
用动力学Boltzmann方程模拟了短强真空紫外脉冲辐照下氙团簇的电离和膨胀动力学。这个统一的模型包括占主导地位的相互作用，有助于集群动力学引起的这种辐射。团簇的大小，$N_{atoms}=20-90000$，和脉冲能量密度，$F=0.05-1.5$ J/cm $^2$，对应的范围内的强度，$10^{12}-10^{14}$ W/cm $^2$和照射时间，$\leq 50$ fs的演化动力学的依赖性进行了研究。与我们的模型得到的预测被发现是在良好的协议与实验数据。我们发现，在曝光的集群形成一个壳结构，包括一个带正电荷的外壳和净电荷等于零的核心。这些壳的宽度取决于簇的大小。带电的外壳在小团簇（$N_{atoms}=20,70$）中很大，它的库仑爆炸驱动了这些团簇的膨胀。在大星系团（$N_{atoms}=2500,90000$）中，中性核很大，在外壳库仑爆炸后，它以流体动力学的方式膨胀。核心内的高电荷离子与电子有效地复合。因此，我们观察到在核心内产生的大部分中性原子，其大小取决于簇的大小。
英文摘要：
Kinetic Boltzmann equations are used to model the ionization and expansion dynamics of xenon clusters irradiated with short intense VUV pulses. This unified model includes predominant interactions that contribute to the cluster dynamics induced by this radiation. The dependence of the evolution dynamics on cluster size, $N_{atoms}=20-90000$, and pulse fluence, $F=0.05-1.5$ J/cm$^2$, corresponding to intensities in the range, $10^{12}-10^{14}$ W/cm$^2$ and irradiation times, $\leq 50$ fs, is investigated. The predictions obtained with our model are found to be in good agreement with the experimental data. We find that during the exposure the cluster forms a shell structure consisting of a positively charged outer shell and a core of net charge equal to zero. The width of these shells depends on the cluster size. The charged outer shell is large within small clusters ($N_{atoms}=20,70$), and its Coulomb explosion drives the expansion of these clusters. Within the large clusters ($N_{atoms}=2500,90000$) the neutral core is large, and after the Coulomb explosion of the outer shell it expands hydrodynamically. Highly charged ions within the core recombine efficiently with electrons. As a result, we observe a large fraction of neutral atoms created within the core, its magnitude depending on the cluster size.
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