1. F. V. Bunkin, V. I. Derzhiev, and S. I. Yakovlenko, ?Prospects of light amplification in the far UV?, Kvantovaya Elektron. (Moscow),8, 1621?1649 (1981).
2. L. I. Gudzenko and L. A. Shelepin, ?Negative absorption in a nonequilibrium hydrogen plasma?, Zh. Eksp. Teor. Fiz.,45, No. 5(11), 1445?1449 (1963).
3. F. E. Irons and N. J. Peacock, ?Experimental evidence for population inversion in C5+ in an expanding laser-produced plasma?, J. Phys.,B7, 1109?1112 (1974).
4. É. Ya. Kononov and K. N. Koshelev, ?Inverted population of multiply charged ion levels?, Kvantovaya Elektron. (Moscow),1, 2411?2416 (1974).
5. É. Ya. Kononov, K. N. Koshelev, Y. A. Levykin, Yu. V. Sidel'nikov, and S. S. Churilov, ?Inverted population of Al XI levels in a laser plasma?, ibid.,3, 576?581 (1976).