Plasma Temperature in Optical Field Ionization of Gases by Intense Ultrashort Pulses of Ultraviolet Radiation

Plasma electron temperatures from 3 eV to [gt]1 keV have been measured or inferred in 10[sup 18]W cm[sup [minus]2] optical field ionization of helium and neon at electron densities ranging from 10[sup 17] to 10[sup 21] cm[sup [minus]3] by laser pulses of 350 fs duration and 248 nm wavelength. Increase of temperature with gas density is dominated at high densities by a combination of nonlinear inverse bremsstrahlung and stimulated Raman scattering heating which are identified as factors limiting progress to shorter extreme ultraviolet laser wavelength in recombination of optical field ionized plasmas.