Population inversions in the Lyman transitions of atomic hydrogen

Population inversions among the excited levels of atoms and ions have been demonstrated by rapid cooling of a plasma. Inversions with respect to the ground level are predicted in ions and atoms as well. The detailed kinetics of such potentially high efficient and short wavelength laser transitions are presented. The feasibility of the laser scheme is discussed in terms of a plasma state diagram. Cooling by adiabatic plasma expansion into vacuum is shown to be limited by recombination heat. Minimal requirements for inversions are derived from the conservation equations and expressed quite generally by the exponent of a generalized isentropic law.