Investigation of population inversion in Al iii for amplified spontaneous emission at 170

Several 2p5(3s3p 3P)2P, 2D core-excited levels of Al iii appear to have large radiative branching ratios to 2p6 3p2P. We propose to produce a population inversion between these levels and amplified spontaneous emission at λ170 by photoionizing the Al ii 2p6 3s3p 3P metastable levels with the N-shell quasicontinuum band of Sb around 125. By pumping with the Sb band, the secondary electron heating of the lasing medium is minimized, which enables a fast collisional depletion of the 2p6 3p 2P levels and a longer-lived inversion. A model of the population kinetics in this scheme indicates that by irradiating a dense and cold Al ii plasma (Ne3×1017 cm-3, Te1.2 eV) with a Sb quasicontinuum pulse of 100-150 ps FWHM and 5×109-1010 W/cm2 peak intensity, gain coefficients between 1 and 3 cm-1 for a duration of 100-150 ps may be obtained. The target parameters are typical for stabilized arc plasmas. The possible extrapolation of this inversion scheme to shorter wavelengths and the use of neutral targets are briefly discussed.