Observation of Gain Coefficient of 15.5 Nm Li-Like al Soft X-Ray Laser in a Recombining Plasma Pumped by a Compact YAG Laser

Various amplification methods for realization of X-ray lasers, such as transient electron collisional excitation (TCE), recombination in a rapid coooling plasma, charge exchange and Auger transition have been proposed and extensively studied experimentally and theoretically, so far, In general, the laser are pumped by plasma media in high-density and high-tenmerature plasmas generated by a high power laser or a electric gas discharge. In our scheme, we employed multi-pulse irradiation technique, where 16 pulse train, pulse width of each pulse: 100 ps (FWHM), pulse separation between each pulse: 200ps, and total energy: <3 J) were irradiated onto the Al slab target. The lasing of this transition was already demonstrated in a high-density and low-temperature Al laser plasma with a low gain coefficient. However, the gain coefficient was as low as 3.2 cm-1 at pump laser energy of 2 J. In order to improve the gain coefficient, we change the seed laser pulse from 100 ps to 400 ps for further heating the laser plasmas. Consequently, it was found that at the laser energy of 3 J, the gain coefficients (g~8.6, 5.5 cm^[-1}) were significantly improved by using longer seed pulse.The 11th International Conference on Inertial Fusion Sciences and Applications (IFSA 2019

Enhancement of water-window soft x-ray emission from laser-produced Au plasma under low-pressure nitrogen atmosphere

To generate bright water-window (WW) soft x rays (2.3–4.4 nm), gold slab targets were irradiated with laser pulses (1064 nm, 7 ns, 1 J). Emission spectroscopy showed that the introduction of low-pressure nitrogen enhanced the soft x-ray yield emitted from the laser-produced Au plasma. The intensity of the WW x-ray transported in a 400-Pa N2 atmosphere from the laser-produced plasma increased by 3.8 times over that in vacuum. Considering a strong x-ray absorption, the x-ray yield emitted directly from the Au plasma in the N2 gas was evaluated to be 13 times higher than that in vacuum. Although similar measurements were made for various gases, only N2 gas causes an increase in a soft x-ray yield. The processes leading to this enhancement mechanism were revealed by using hydrodynamic simulation and atomic structure codes