激光脉冲对内层等离子体辐射源的影响

An effect of laser profile on plasma radiation source

本文的基本思想是设计双层金铝薄膜靶以检测激光脉冲宽度与等离子体消融深度的关系 ,找出有效的等离子体加热方法以产生更强更亮的等离子体辐射源。由于有预脉冲激光的存在 ,表层金薄膜首先被消融 ,由主脉冲携带的大能量就能较易穿过表层金等离子体将能量聚焦在内层铝靶上 ,由此产生内层高温等离子体。又由于外层低温等离子体存在 ,其将有效的阻碍内高温等离子体因膨胀而引起的能量损失。对无预脉冲而言 ,直接入射激光能量都沉积在靶表层形成表层高温等离子体。但是激光直接入射而产生的等离子体辐射总强度只比由预脉冲情况下产生的金等离子体辐射强度增加 1 5 %。而预脉冲能量只占激光总能量的 2 %。实验结果显示Al光谱线主要来自类氢 ,类氦离子跃迁。Au等离子体光谱线主要来自它的N带 ,O带和P带谱。我们也观察到一个明显的软X射线短波发射极限。

The aim of this paper is to study an effect of laser profile on plasma radiation source. A high power laser with a tiny prepulse laser has been used to irradiate Au covered (150 nm) Al target. After low-density plasma on the surface of target was produced by prepulse, main pulse of strong laser can easily pass through surface plasma and directly heat inside Al thin film. Strong emission from inter-Al-layer plasma has bccn obscrvcd. In contrast, Only Au plasma N-,O- and P-band cmissions wcrc dctcctcd if Au covered Al target was directly irradiated by laser beam, indicating hot plasma only appears on the surface. experimental data also indicated that Au plasma emission heated by prepulse was strong even though the total energy of the prepulse was only 2% of main laser pulse energy. A limitation of short wave emission of Au plasma source was also observed.