Design considerations for z-pinch driven photoresonant x-ray lasing in neonlike krypton

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Abstract
A neonlike x‐ray laser photoresonant pumping scheme is explored. An attractive design is a coaxial z‐pinch consisting of an inner krypton lasant plasma surrounded by a carbon shell that itself is surrounded by a stagnated krypton plasma. The photoresonant radiation emitted from the outer plasma passes inwardly through the carbon shell and photoexcites lasant electrons to the 3s, 3d, and 4d levels. It is calculated that monochromatic pump powers of 30 GW/cm eV can be achieved for the 4d neonlike resonance line while powers of 100–200 GW/cm eV are attainable for the 3s and 3d resonance lines. The gain in several neonlike 3s‐3p transitions is calculated as a function of temperature and density of the lasant plasma. Reasonable gain in only the 3p‐3s (J=0–1) transition is obtained for high‐density, high‐temperature lasant conditions. This gain, which is driven by monopole excitation from the ground state to the 3p (J=0) level, is nearly independent of the presence of pump radiation. For low‐density, low‐temperature lasants, optimal gain is obtained in the 3p‐3s (J=2–1) transitions. Under these conditions, the pump radiation is necessary to photoionize and photoexcite the lasant plasma to the neonlike stage while radiative decay from the resonantly pumped 4d level to the 3p (J=2) states provides the major upper lasing level pump mechanism.