Saturation and Kinetic Issues for Optical-Field-Ionized X-Ray Lasers

Ultrashort (tp ≤ 100 fs) high intensity (I ≥ 1017 W/cm2) lasers are potential drivers for x-ray lasers with wavelengths below 100 Å. The short wavelengths are obtained by lasing down to the ground state of the ion. We address a number of saturation and kinetic issues that arise from this type of laser. One scheme, that we have consider in detail, is lasing in the 3d - 2p transitions in Li-like Ne at 98 Å. We have found that for a UV driver (λ = 0.25 µm) stimulated Raman heating is reduced sufficiently to obtain high gains and reasonable efficiencies. Raman heating is a potential barrier for extending the scheme to shorter wavelengths due to the required higher intensities and corresponding increase in heating.