激发态之间的电离与复合过程对类氖锗19.6nm X射线激光增益系数的影响

Effect of ionization and recombination between excited states on gain of 19.6 nm X-ray laser

考察了激发态之间的电离与复合过程对等离子体状态的影响,并对其原因进行了细致的分析,分别考察了对1.0ns,100ps和5ps激光驱动的类氖锗19.6nm X射线激光增益系数的影响.研究表明,对于5 ps激光驱动的瞬态机理X射线激光来讲,因增益区处在高密度区,所以,激发态之间的电离与复合过程对X射线激光将不可以忽略.对于1.0ns和100ps激光驱动的亚稳态机理X射线激光来讲,在电子密度小于等于5×1020cm-3的区域,忽略激发态之间的电离与复合使增益的时间半高全宽延长了~10%,峰值增益的空间半高全宽分别增加了~13%和^-23%,相对于增益的维持时间(半高全宽),峰值增益出现的时间分别延迟了~1.4%和~6.9%,差异并不十分显著,因此矩阵分块法可以对亚稳态机理X射线激光进行粗略地、规律性地研究,但是准确地模拟还是不能忽略激发态之间的电离与复合过程,且如果关心等离子体电离的全过程,则激发态之间的电离与复合过程不能忽略.

As it is difficuh to solve a large number of rate equations including doubly excited states of various ions, block matrix method is expected to dramatically reduce the machine time by dividing the large number of equations into pieces of small units, and solving them one by one, on condition that the ionization and recombination between excited states of ions can be ignored. In this paper, the influence of ionization and recombination between excited states on plasma status was studied, and detailed analysis of its mechanism was made. The effect on gain of Ne-like Ge 19.6 nm X-ray laser respectively driven by 1.0 ns pulse, 100 ps pulse and 5 ps pre-pulse and main pulse was studied. The simulation shows that for the 5 ps driving pulse case, the ionization and recombination between excited states has relatively large influence, and it can not be ignored and that for the two quasi-stable state cases, in the gain region with electron density less than 5×10^20 cm^-3, the FWHM temporal width of gain increases by - 10%, and the FWHM spatial width of gain increases respectively by - 13% and - -23%, and the time the peak gain appears is delayed respectively by - 1.4% and - 6.9%, which is tolerable, implying that the block matrix method could be applied in the qualitative modeling of QSS scheme X-ray laser. However, for accurate study, the ionization between the excited states could not be neglected.