Exploding-Foil Technique for Achieving a Soft X-Ray Laser

We describe a design for producing a soft x-ray laser via 3p-3s transitions in Ne-like selenium (wavelength of about 200 {}). A 0.53-{μ} m laser, focused in a 1.2×{}0.02-cm spot to {~} 5×{}10¹³ W/cm², 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 cm^-1 are predicted for various transitions.