Extreme ionization of Xe clusters driven by ultraintense laser fields.
Extreme ionization of Xe clusters driven by ultraintense laser fields.
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DOI：
10.1063/1.2762217
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发表时间：
2007-08
期刊：
影响因子：
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通讯作者：
A. Heidenreich;I. Last;J. Jortner
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文献类型：
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作者：
A. Heidenreich;I. Last;J. Jortner
我们应用理论模型和分子动力学模拟，探索了在超强红外高斯激光场(峰值强度I(M)=10(15)-10(20) W cm（-2)，时间脉冲长度tau=10-100 fs，频率nu=0.35 fs(-1)）驱动下Xe(n)团簇（n=2-2171，初始团簇半径R(0)=2.16-31.0 A）中的极端多电子电离。团簇化合物的电离过程分为内电离、纳米等离子体形成和外电离三个过程。内电离产生高电离能级(形成q=2-36的[Xe(q+)](n))，可通过实验观察得到。簇大小和激光强度对内电离能级的依赖是由势垒抑制电离（BSI）和电子冲击电离（EII）的叠加引起的。BSI是由激光场和离子、电子内场的复合场诱导产生的，表现出点火增强和筛选延迟效应。EII用实验横截面处理，适当考虑顺序冲击电离。在最高强度下(I(M)=10(18)-10(20) wcm(-2))，内电离以BSI为主。在较低强度下(I(M)=10(15)-10(16) wcm(-2))，纳米等离子体持续存在，EII对内电离产率的贡献很大。它随着团簇大小的增加而增加，对[Xe(q+)](n)电离能级的增加有显著影响，在团簇中心最为明显，并随着脉冲长度的增加而显著增加（即在tau=100 fs时，成为Xe（2171）的主要电离通道（56%））。随着激光强度的增加，EII产率和电离能级增强减小。在I(M)=10(15)-10(16) wcm（-2）时，EII产率与脉冲长度的关系建立了极端电离产物的超强激光脉冲长度控制机制。
We applied theoretical models and molecular dynamics simulations to explore extreme multielectron ionization in Xe(n) clusters (n=2-2171, initial cluster radius R(0)=2.16-31.0 A) driven by ultraintense infrared Gaussian laser fields (peak intensity I(M)=10(15)-10(20) W cm(-2), temporal pulse length tau=10-100 fs, and frequency nu=0.35 fs(-1)). Cluster compound ionization was described by three processes of inner ionization, nanoplasma formation, and outer ionization. Inner ionization gives rise to high ionization levels (with the formation of [Xe(q+)](n) with q=2-36), which are amenable to experimental observation. The cluster size and laser intensity dependence of the inner ionization levels are induced by a superposition of barrier suppression ionization (BSI) and electron impact ionization (EII). The BSI was induced by a composite field involving the laser field and an inner field of the ions and electrons, which manifests ignition enhancement and screening retardation effects. EII was treated using experimental cross sections, with a proper account of sequential impact ionization. At the highest intensities (I(M)=10(18)-10(20) W cm(-2)) inner ionization is dominated by BSI. At lower intensities (I(M)=10(15)-10(16) W cm(-2)), where the nanoplasma is persistent, the EII contribution to the inner ionization yield is substantial. It increases with increasing the cluster size, exerts a marked effect on the increase of the [Xe(q+)](n) ionization level, is most pronounced in the cluster center, and manifests a marked increase with increasing the pulse length (i.e., becoming the dominant ionization channel (56%) for Xe(2171) at tau=100 fs). The EII yield and the ionization level enhancement decrease with increasing the laser intensity. The pulse length dependence of the EII yield at I(M)=10(15)-10(16) W cm(-2) establishes an ultraintense laser pulse length control mechanism of extreme ionization products.