Plasma electron temperatures from 3 eV to >1 keV have been measured or inferred in ${10}^{18}$ W ${\mathrm{cm}}^{-2\mathrm{}}$ optical field ionization of helium and neon at electron densities ranging from ${10}^{17}$ to ${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$ 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.

• Received 9 August 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.554