Wavelength and intensity dependence of multiple forward scattering of electrons at above-threshold ionization in mid-infrared strong laser fields

The contribution of multiple forward scattering in Coulomb focusing of low-energy photoelectrons at above-threshold ionization in mid-infrared laser fields is investigated. It is shown that the high-order forward scattering can have a nonperturbative effect in Coulomb focusing. The effective number of rescattering events is defined and is shown to depend weakly on laser intensity and wavelength. Nevertheless, the relative contribution of forward scattering in Coulomb focusing and the Coulomb focusing in total decrease with increasing laser intensity and wavelength.