| Research Abstract |
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.
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