文档介绍：摘要
随着超短脉冲激光的发展,Tabak 等人提出了激光聚变“快点火”方案。根据该思
想,用超短脉冲激光与等离子体相互作用产生的超热电子点燃热核燃料是一个可行的
途径。因此在强场物理的研究中,超热电子的能量、产额和发射方向等都是人们关注
的焦点。在超热电子与靶的作用中产生的硬 X 射线或γ射线已成为获取超热电子信息
的一种有效手段。
本文描述了超短脉冲激光与固体靶相互作用实验研究的实验装置和 X 射线能谱
的测量方法。采用铅屏蔽和符合技术,把本底计数几率降低到10−4 / 发。在激光强度
I ≈× 1016 W/cm 2 ,λ= 746nm 的 P 极化光以 45D 入射角照射厚为 5mm 的铜靶、探测
立体角为 ×10-6rad 的实验条件下,产生的硬 X 射线的能量主要集中在低于 100kev
的能量范围内,其中单光子计数占探测到的总光子数的 95%。用双温麦克斯韦分布对
实验结果进行拟和,得到两群温度分别为Ta1 = ± 和Ta2 =± 的超
热电子群。经理论分析,实验结果中的高温电子群与共振吸收产生超热电子的定标率
相符,故实验结果中的高温电子群可能是通过该机制产生的;而低温部分可能是激光
与等离子体相互作用时,等离子体中的电子在激光电场的作用下发生抖动运动而产生
的。
关键词: 超短脉冲激光,固体铜靶,硬 X 射线能谱,超热电子,HPGe 探测器
I
Abstract
With the development of ultra-short pulse laser, Tabak brought forward the idea of
“fast ignition”. According to his assumption, it’s possible to ignite the nuclear fuel with the
hot electrons produced by the interaction between the laser and plasma. So, in the
community of strong field physics, the characteristic of hot electrons such as temperature,
quantity and direction of emission is always the focus of people’s interest. The hard X-ray
produced by the interaction between hot electrons and solid targets is often used to deduce
the information about hot electrons.
This paper describes the experimental facilities and measuring methods of X-ray
detection. The count per shot due to background noise was reduced to 10 −4 / shot by
applying the techniques of shielding and linear gate. The intensity of the P polarized light is
about I ≈× 1016 W/cm 2 , λ= 746nm .The experimental result shows that the energy of
X ray is almost less than 100kev and the temperature of hot electrons are ± and
± KeV respectively, under the condition that the angle of incidence of laser is about
45D and the solid angle of detection is about ×10-6. The probability of single photon is
about 95%. Based on theoretical analysis, resonance absorption is probably the dominant
process for hot electron ge