Population Inversion in High Density Recombining Plasmas

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The main purpose of this project is to investigate the dominant processes leading to the population inversion in recombining plasmas for development of the short-wave laser. We have made both theoretical and experimental studies on the recombining plasmas produced by interaction of high density plasmas with neutral gases. The main results obtained in this project are as follows :1. A simulation using a CR model has shown that laser oscillation between the hydrogen levels n=2 and 3 can be genarated in a recombining hydrogen plasma interacting with a dense helium gas as a cooling medium.2. The optimum condition of initial electron density and temperature. decay time and plasma shape for VUV coherent laser oscillation has been presented for <He^+> recombining plasma. The continuous coherent laser of He <II> 164nm line which corresponds to the transition n=3->2 in <He^+> is possible if a sufficiently thin sheet plasma flow in a steady state with the electron density of <10^(15)> - <10^(16)> <cm^(-3)> is cooled down to 0.2eV with decay time of <10^(-7)> [ <10^(-8)> s. 3. A helium recombining plasma of <n_e> = <10^(16)> <cm^(-3)> and <T_e> =4eV has been produced by a Z-pinch gun plasma injected into a helium neutral gas of 0.26 Torr. Strong population inversion was found between <He^+> n=4 and 5 levels. The one-pass gain was estimated for a 3cm plasma column. and found to exceed a threshold for the laser oscillation if a pair of mirrors with reflectivity of 99% and 99.8% was installed.4. The present experimental results suggest that the electron temperature of the recombining plasma will be cooled down to less than leV by introduction of much more dense hydrogen gas through a fast acting valve into the Z-pinch device. Then. strong inversion between <He^+> n=2 and 3 levels will be possible.