SFA APPLIED TO THE NONSEQUENTIAL DOUBLE-IONIZATION OF THE HELIUM ATOMBY A CIRCULARLY-POLARIZED PLANE-WAVE

We calculate the total direct double photoionization rates in the stro ng field approximation for the helium atom in an intense field of a ci rcularly polarized plane wave. We study the role of the electron-elect ron interaction both in the initial and the final states. We find that for the frequencies and intensities considered here, the initial elec tron-electron correlation can be neglected, while the repulsion in the final state changes the total rate only quantitatively, and becomes i rrelevant as frequency grows. The electron energy spectra are also obt ained.