Population Inversion in High Density Recombining Plasmas

该项目的主要目的是研究在发展短波激光的复合等离子体中导致布居反转的主要过程。我们对高密度等离子体与中性气体相互作用产生的复合等离子体进行了理论和实验研究。主要结果如下：1.用CR模型模拟表明，在以致密氦气体为冷却介质的复合氢等离子体中，氢能级n=2和n=3之间的激光振荡可以产生。初始电子密度和温度的最佳条件。给出了~lt；He~+&Gt；复合等离子体的VUV相干激光振荡的衰减时间和等离子体形状。如果电子密度为&lt；10^(15)&gt；-10^(16)&gt；的足够薄的片状等离子体流在稳态冷却到0.2 eV，衰减时间为&lt；10^(-7)&gt；[&lt；10^(-8)&gt；用Z-夹点枪等离子体注入0.26Torr的氦中性气体，产生了~lt；N_e&gt；=&lt；10^(16)&gt；cm^(-3)&gt；和&lt；T_e&gt；=4 eV的氦复合等离子体。~lt；He^+&gt；n=4~5级之间存在较强的种群反转现象。对3 cm等离子体柱的单程增益进行了估算。发现如果安装一对反射率分别为99%和99.8%的反射镜，激光振荡的阈值将超过阈值。目前的实验结果表明，通过在Z-Pinch装置中引入更稠密的氢气，复合等离子体的电子温度将被冷却到低于Lev的水平。然后。&lt；He^+&gt；n=2和3级之间的强烈反转将是可能的。

The main purpose of this project is to investigate the dominant processes leading to the population inversion in recombining plasmas for development of the short-wave laser. We have made both theoretical and experimental studies on the recombining plasmas produced by interaction of high density plasmas with neutral gases. The main results obtained in this project are as follows :1. A simulation using a CR model has shown that laser oscillation between the hydrogen levels n=2 and 3 can be genarated in a recombining hydrogen plasma interacting with a dense helium gas as a cooling medium.2. The optimum condition of initial electron density and temperature. decay time and plasma shape for VUV coherent laser oscillation has been presented for <He^+> recombining plasma. The continuous coherent laser of He <II> 164nm line which corresponds to the transition n=3->2 in <He^+> is possible if a sufficiently thin sheet plasma flow in a steady state with the electron density of <10^(15)> - <10^(16)> <cm^(-3)> is cooled down to 0.2eV with decay time of <10^(-7)> [ <10^(-8)> s. 3. A helium recombining plasma of <n_e> = <10^(16)> <cm^(-3)> and <T_e> =4eV has been produced by a Z-pinch gun plasma injected into a helium neutral gas of 0.26 Torr. Strong population inversion was found between <He^+> n=4 and 5 levels. The one-pass gain was estimated for a 3cm plasma column. and found to exceed a threshold for the laser oscillation if a pair of mirrors with reflectivity of 99% and 99.8% was installed.4. The present experimental results suggest that the electron temperature of the recombining plasma will be cooled down to less than leV by introduction of much more dense hydrogen gas through a fast acting valve into the Z-pinch device. Then. strong inversion between <He^+> n=2 and 3 levels will be possible.