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We report observations of amplified spontaneous emission at soft x-ray wavelengths. An optical laser ionized thin foils of selenium to produce a population inversion of the 2p^53p and 2p^53s levels of the neonlike ion. Using three time-resolved, spectroscopic measurements we demonstrated gain-length products up to 6. 5 and gain coefficients of 5. 51. 0 cm^-1 for the J=2 to 1 lines at 206. 3 and 209. 6. We also observed considerable amplification for the same transitions in yttrium at 155. 0 and 157. 1.
Matthews et al. (Mon,) studied this question.