Described is a high gain, soft X-ray pumped, inner-shell, photoionization amplifier/laser in Cd or Zn vapors. The soft X-ray photoionization, generated by a laser-produced plasma or other high intensity X-ray source, preferentially removes inner-shell d-electrons from neutral atoms leaving them ionized in a .sup.2 D state and producing a population inversion with respect to a lower lying .sup.2 p state. Also described are techniques for achieving inversions with respect to the ion ground state of Cd, Zn or Hg by optically pumping from the inner-shell ionized state to a higher energy level. Iso-electronic scaling of Cd, Zn and Hg suggests similar lasing phenomena exist, for example, in Ga, In and Tl ions, respectively, and also higher iso-electronic sequences.
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