We describe a design for producing a soft x-ray laser via $3p-3s$ transitions in Ne-like selenium (wavelength of about 200 Å). A 0.53-μ m laser, focused in a 1.2×0.02-cm spot to ∼ 5×${10}^{13}$ W/${\mathrm{cm}}^2$, heats and burns through a thin foil of Se. Besides ionizing the Se to a Ne-like state, the laser explodes the foil, creating a region of uniform electron density. This allows propagation of the x rays down the 1-cm-long gain direction without debilitating refraction. Gains of 4 to 10 ${\mathrm{cm}}^{-1\mathrm{}}$ are predicted for various transitions.

• Received 26 October 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.106