A strong-field theory is extended to the description of energetic photoelectron spectra. Experimental spectra are accurately described for both linear and circular polarizations, subject only to a single adjustment of reported peak laser intensities. Examined are single and (sequential) double ionization of helium, to energies of about 1 keV. An approximation of the spectrum as a Maxwellian distribution yields a temperature dependent on the spectrometer viewing angle. Final-state Coulomb effects in circular polarization are examined.

• Received 15 May 1996

DOI:https://doi.org/10.1103/PhysRevA.54.R1765