相对论飞秒激光辐照表面调制靶产生高定向性正电子束

Production of highly-directional positron beam by relativistic femto-second laser irradiating micro-structured surface target

激光驱动的正电子源具有高产额、短脉宽、高能量的优点。采用粒子模拟和蒙特卡罗模拟相结合的方法,对相对论飞秒激光与表面具有微米丝阵结构的调制靶相互作用产生正电子束的过程进行了全三维的模拟研究。结果表明,在激光能量约3.2 J、脉宽约为40 fs的情况下,可得到产额为1011量级、最大能量达120 MeV的超热电子束,其轰击高Z转换靶可达到产额为109量级、截止能量约50 MeV的正电子,且正电子的发散角仅为4.92°。相比于平板靶,表面调制靶的使用可以提高正电子的产额、能量和定向性。

Laser driven positron source has the advantages of high yield, short pulse width and high energy. In this paper, particle-in-cell simulation and Monte-Carlo simulation are combined to simulate the process of positron production in the interaction of relativistic femtosecond laser with a micro-structured surface target(MST) with a micron-scale wire array on the surface. The results show that when the laser energy is about 6 J and the pulse width is about 40 fs, fast electrons with the yield of 1011 orders of magnitude and the cut-off energy of about 120 MeV can be obtained. When the electrons bombard a high-Z conversion target, positrons with the yield of 109 orders of magnitude,and cut-off energy about 50 MeV are obtained. The divergence angle of the positron beam is 4.92°. Compared with planar targets, the use of MSTs can benefit the yield, energy and directivity of positrons.