In this paper, we present the mechanisms of ionization of a thin gold film irradiated by a high-intensity, short-pulse laser in the range of I = 10 20 − 22 W / cm 2 and the associated acceleration of multiply charged gold ions. A numerical one-dimensional simulation using an extended particle-in-cell code, which includes atomic and collisional relaxation processes, indicates that two types of acceleration, hole-boring radiation pressure acceleration (RPA) and target normal sheath acceleration (TNSA), contribute to the generation of highly charged ions with kinetic energies on the order of 10 MeV/u. In each acceleration, a longitudinal electrostatic field excited by different mechanisms dominantly ionizes atoms to higher charge states and accelerates them to the vacuum region from the rear surface, which is opposite the front surface irradiated by the laser field. The field ionization process dominantly ionizes high energy ions to the high charge state, while a large number of ions with energy < 1 MeV / u are ionized by an electron impact ionization process. In TNSA, a multiply charged ion generated at the rear surface is accelerated to the maximum energy although the ion with the highest charge state is generated at the front surface in RPA. However, the existence of contamination, such as water vapor, suppresses the ion energy of TNSA to less than that of RPA since the sheath field readily accelerates the protons and oxygen prior to the acceleration of the gold ions. Our derived theoretical scaling describes the maximum ion energy for each charge state in the cases with and without contamination using the relationship between the longitudinal electrostatic field profile near the rear surface and the classical tunnel field ionization model.

中文翻译：

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高强度激光辐照固体薄膜中多电荷金离子的电离与加速

在本文中，我们介绍了由 I = 10 20 - 22 W / cm 2 范围内的高强度短脉冲激光照射的金薄膜的电离机制以及多电荷金离子的相关加速。使用包含原子和碰撞弛豫过程的扩展粒子内代码的数值一维模拟表明，两种类型的加速度，钻孔辐射压力加速度 (RPA) 和目标法向鞘加速度 (TNSA)，有助于产生动能约为 10 MeV/u 的高电荷离子。在每次加速中，由不同机制激发的纵向静电场主要将原子电离到更高的电荷状态，并将它们从背面加速到真空区域，与激光场照射的前表面相对。场电离过程主要将高能离子电离到高电荷态，而大量能量 < 1 MeV / u 的离子通过电子碰撞电离过程电离。在 TNSA 中，尽管在 RPA 的前表面产生具有最高电荷态的离子，但在后表面产生的多电荷离子被加速到最大能量。然而，水蒸气等污染物的存在将 TNSA 的离子能量抑制到低于 RPA 的离子能量，因为鞘场很容易在金离子加速之前加速质子和氧气。