强激光与高密度气体相互作用中电子和离子加速的数值模拟

在现有的一维粒子模拟程序的基础上发展了带光电离和碰撞电离及蒙特卡罗两体碰撞的模拟程序(1D PIC-MCC). 用此程序模拟研究了短脉冲激光与He气靶相互作用时电子和离子的加速过程. 研究表明当强激光与过临界密度的微米厚度的平面靶相互作用时，靶前表面物质将被激光脉冲前沿迅速离化；新生的电子被激光场有质动力加速成为高能电子，这些电子穿入到靶内，通过电子碰撞电离离化靶内物质；一部分高能电子穿透靶后，会在靶的后表面形成强的电荷分离场，该场迅速离化靶后表面物质，同时使得后表面离子得到加速. 部分穿透靶的超热电子将被电荷分离场重新拉回靶内，在靶的前后表面振荡. 一些振荡电子在此过程中得到电荷分离场加速，离开前表面，在前表面也形成电荷分离场，使前表面离子得到加速. 关键词： 激光等离子体 光电离和碰撞电离 电子加速 离子加速

Numerical simulation of acceleration of electrons and ions in the interaction of intense laser pulses with dense gaseous targets

Using a one-dimensional particle-in-cell code, which includes field ionization and electron collisional ionization, as well as elastic binary Coulomb collisions, we study the acceleration of electrons and ions by the interaction of an intense laser pulse (10¹⁷—10¹⁸W/cm², 26.7fs) with a helium gas target (10²¹—10²²/cm³, 0.8 μm thick). It is shown that field ionization appears quickly at the target front surface. Collisional ionization is found inside the target by energetic electrons, which are accelerated by the laser fields at the front surface and transported into the target. Part of these electrons transmits through the target rear surface and induces an electrostatic field there. This field further leads to field ionization at the rear surface. Meanwhile, it accelerates new-born ions produced there through the field ionization. Because of the electrostatic fields induced at the two target surfaces, some electrons oscillate between them, resulting in oscillating energy exchange between electrons, ions and the electrostatic fields. Particular attention is also paid to the origins of accelerated ions. Under certain conditions, ions accelerated inside the target are more energetic than those accelerated at the target surfaces.