Electron spectra of above-threshold ionization in elliptically polarized laser fields

Measurements of electron spectra of above-threshold ionization in an elliptically polarized laser field are reported and discussed in terms of theoretical models. For low energies, the electron yields in the direction of the large component of the elliptically polarized field first decrease when the ellipticity increases and then rise again when circular polarization is approached. A classical explanation of this effect is provided. The same electron yields display, while they are decreasing as a function of the ellipticity, characteristic shoulders and ripples. These features can be related to quantum mechanical interference of electrons tunneling out into the continuum at different times within one cycle of the field. Electron yields for high energies, those that are part of the plateau, drop very quickly with increasing ellipticity at a rate almost independent of the energy. This is fully explained by spreading of the electronic wave function. A first example of the electron spectrum as a function of energy and angle of emission for fixed ellipticity is presented, too.