HIGH-INTENSITY ABOVE-THRESHOLD IONIZATION OF HE

This is the first high resolution measurement of the electron energy s pectrum from high intensity above-threshold ionization (ponderomotive energy >> ionization potential >>hv) at intensities up to 7 x 10(15) W /cm2. In contrast to previous work, we have used a short pulse and a l arge focal spot along with low gas densities to minimize the effect of ponderomotive forces and collisions. Existing models do not agree wel l with electron energy spectra for either linearly or circularly polar ized light. The electron temperature is too hot for the implementation of 820 nm multiphoton ionized recombination type XUV laser schemes.