Study on an efficient keV X-ray laser from a cluster target pumped by a table-top high-power laser

在软X射线区，X射线激光已经成功地实现了振荡。然而，在硬X射线区(kev区)，情况并非如此。在kev X射线激光中产生了振荡。必须开发高效的抽水方法。然后，我们研究了新的X射线激光方案，在该方案中，通过多光子内壳层激发过程来激发keV X射线区的布居反转。为了在保持10^&lt；18&gt；W/cm^2的强光场的情况下使增益长度变长，我们还研究了相对论电荷位移自沟道。对于多光子内层激发，研究了Xe团簇靶的M壳层和L壳层发射的波长依赖性。用行波掺钛蓝宝石激光器测量了KEV X射线能谱。通过与KrF激光器的结果比较，证明了激光对X射线的转换效率很小。在M壳层发射中，钛宝石的转换效率比KrF和L壳层的转换效率分别小-10倍和-3倍。这些结果对于KeV X射线激光器的发展具有重要意义。为了研究相对论激光沟道和电荷位移激光沟道，我们测量了行波钛激光脉冲传输的时间分辨背光图像。为了驱动自沟道，注入的激光功率必须大于一个强烈依赖于等离子体密度的临界功率。测量结果表明，在Xe团簇靶中，当靶气体密度足够高时，似乎发生了相对论和电荷位移自沟道现象。

In the soft x-ray region, x-ray lasers have been already succeeded in the oscillation. However, in the hard x-ray region (the keV region), it is not. For having an oscillation in the keV X-ray laser. the efficient pumping method has to be developed. Then we studied on the new x-ray laser scheme, in which the population inversion in the keV X-ray region is excited by the multiphoton innershell excitation process. A relativistic and charge-displacement sell-channeling is also studied for making the gain length long with keeping the intense optical field of 10^<18> W/cm^2.For the multiphoton innershell excitation, the wavelength dependence of M- and L-shell emission from Xe cluster target has been studied. KeV X-ray spectra have been measured with using a TW Ti : sapphire laser. By comparing with the results with a KrF laser, the conversion efficiencies from a laser light to X-rays are proved to be small. In M-shell emission, the conversion efficiency in Ti : sapphire was -10^<-2> times smaller than that in KrF, and in L-shell -1O^<-3> times. These results are thought to be very important for the development of the keV X-ray laser.For the study on the relativistic and charge-displacement laser channeling, we measured the time-resolved backlighted image of the propagation of the TW Ti : sappghire laser pulse. In order to drive the self-channeling, the injected laser power must be larger than a critical power which strongly depends on the plasma density. From the results of our measurement, it was proved that, in Xe cluster target, the relativistic and charge displacement self-channeling seemed to happen, when the target gas density becomes high enough.