Soft X-ray Laser by Hybrid Excitation Method Using Laser Produced Multiple Charged Ions

我提出了一种混合激发方法作为实现软x射线激光器的新方法，其中高强度激光产生的多个带电离子由小型放电装置的电力进一步激发。本文首次观测到Ar_2^<**>在126nm处的发射，并伴有高次谐波信号。聚焦激光强度对Ar准分子强度的依赖性与隧道电离理论（即ADK理论）的预测非常吻合。因此，我发现Ar准分子的产生是由高强度激光产生的电子引发的，这些电子可能成为电子束装置产生的电子的替代品。众所周知，隧道电离产生的电子温度对激光强度、波长和偏振非常敏感。然而，实验数据表明，当线性放大和圆偏振的激光束与Ar相互作用时，Ar准分子的发射没有差异。从理论上考虑高强度激光产生的等离子体中电子的能量输运，发现等离子体的快速导电冷却对准分子的产生起着重要的作用。制备合适的准分子所需的冷却时间常数比三体复合时间常数快得多，而三体复合时间常数是准分子的主要制备过程。为了模拟放电等离子体的x射线发射与稀有气体（Kr）之间的相互作用，采用激光产生等离子体的x射线源作为紧凑的x射线源。当激光等离子体发射软x射线激发Kr原子时，观察到以147 nm为中心的Kr准分子发射和以157nm为中心的Kr^<2+>发射。这些发射的时间分辨数据显示，两者的上升速度与等离子体引发激光的上升速度一样快，表明等离子体的软x射线发射直接产生离子/准分子。这可能是有利的，因为准分子的产生不太受电子去激发过程的影响。基于光电离模型，Kr^<2+>离子是由Kr 4p电子的光电离产生的。这种离子的产生启动了离子通道产生准分子的动力学。少

I have proposed a hybrid excitation method as a new method to realize a soft x-ray laser where high intensity laser produced multiple charged ions are further excited by electrical power from a compact discharge device.As a result of the interaction of Ar and high intensity laser field, I have observed emission from Ar_2^<**> at 126 nm for the first time together with some signals of high order harmonics. The focused laser intensity dependence of the Ar excimer intensity agrees well with that predicted by a tunnel ionization theory so called ADK theory. I,therefore, found out that the production of Ar excimers was initiated by high intensity laser produced electrons, which may become a substitution to those produced by an electron beam device.It is well known that the electron temperature as a result of tunnel ionization is very sensitive to laser intensity, wavelength, and polarization. Experimental data, however, show no difference in terms of the Ar excimer emission when linearly po … More larized and circularly polarized laser beams interacted with Ar. Considering about the energy transport of electrons in a high intensity laser produced plasma theoretically, I have found out a rapid conductive cooling of a plasma plays an important role for the excimer production. A cooling time constant for the appropriate excimer production is much faster than the three body recombination time constant which is a main production process of the excimers.In order to simulate an interaction between x-ray emission from a discharge plasma and rare gas (Kr), an x-ray source using laser produced plasma was used as a compact x-ray source. When Kr atoms were excited by soft x-ray emission from a laser produced plasma, Kr excimer emission centered at 147 nm was observed as well as emission from Kr^<2+> at 157nm.Time resolved data of these emissions show both rise times as fast as that of a plasma initiating laser, indicating the direct ion/excimer production by soft x-ray emission from a plasma. This may be advantageous because the excimer production is not much affected by an electron deexcitation process. Based on a photoionization model, the Kr^<2+> ions are produced by photoionization of Kr 4p electrons. This ion production initiates the excimer production kinetics by ionic channels. Less