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

在软X射线领域，X射线激光已经在振荡方面取得了成功。然而，在硬X射线区域（keV区域），它不是。在千电子伏的X射线激光器中产生振荡。必须开发有效的泵送方法。然后研究了keV X射线区域的粒子数反转由多光子内壳层激发过程激发的新的X射线激光方案。研究了相对论性和电荷位移自沟道效应，在保持10^ W/cm ^2强光场的条件下，获得了较长的增益长度<18>。在多光子内壳层激发下，研究了团簇靶M壳层和L壳层发射的波长依赖性。用TW钛宝石激光器测量了KeV的X射线谱。通过与KrF激光器的结果比较，证明了从激光到X射线的转换效率很小。在M壳层发射中，Ti：蓝宝石中的转换效率比KrF中的转换效率小约10 ^<-2>倍，并且在L壳层中小约10 ^<-3>倍。这些结果对于keV X射线激光器的发展具有重要意义。为了研究相对论和电荷位移激光沟道效应，我们测量了TW钛宝石激光脉冲传输的时间分辨背光源图像。为了驱动自沟道，注入的激光功率必须大于临界功率，该临界功率强烈地依赖于等离子体密度。实验结果表明，当靶气体密度足够大时，在团簇靶中似乎会发生相对论性和电荷位移自沟道效应。

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.