Line profiles of soft-x-ray laser gain coefficients

Spectral profiles of gain coefficients at soft-x-ray wavelengths near 200 A{} in laser-driven exploding foils and laser-produced magnetically confined plasma columns are shown not only to be influenced by thermal Doppler broadening, but very likely also by collisional narrowing of some lines and by Doppler effects from hydrodynamic turbulence. The multiply charged ions, z=24 and 5, in these dense and relatively low-temperature plasmas are highly collisional, with ion-ion mean free paths of about 20 and 200 A{}, respectively. They involve plasma flows with Reynolds numbers {}10⁵. Collisional narrowing and turbulent broadening may have combined to spoil the predicted gain of the {λ}=183 A{} selenium line in the foil experiment. Any turbulent flow must have a fundamental wavelength exceeding a critical size ranging from {~}40 {μ}M for the 206- and 209-A{} selenium lines to {~}90 {μ}m for the 183-A{} selenium line for observable gain to occur in the single-pass oscillator experiments.