Above-threshold ionization of multiply charged ions in the tunneling regime: The Coulomb modification of the spatial spectra of relativistic photoelectrons

The spatial distributions of above-threshold photoelectrons produced through the tunneling ionization of multiply charged ions in laser fields of relativistic intensity are theoretically investigated. It is demonstrated that the interplay of relativistic effects and the Coulomb interaction of photoelectrons with a parent ion substantially modifies the spatial distribution of electrons. In a short laser pulse, this distribution displays a two-peak structure. The positions of the peaks in the spatial distribution depend on the intensity and ellipticity of laser radiation. These positions are also determined by the charge of a parent ion, which can be employed to monitor the ionization of multielectron atoms. It is shown that stabilization of a new type may occur in the ionization of multiply charged ions with ultrashort pumping pulses: gradient forces on the trailing edge of the pulse may compensate for the forward relativistic drift of a photoelectron, while the Coulomb forces may lead to the trapping of an electron on a closed orbit after the termination of the pumping pulse.