Symmetries in elastic scattering of electrons by hydrogen atoms in a two-color bicircular laser field

Abstract

We consider the elastic scattering of electrons by hydrogen atoms in the presence of a two-color circularly polarized laser field in the domain of moderate intensities below ${10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ and high projectile energies. A hybrid approach is used, where for the interaction of the incident and scattered electrons with the laser field we employ the Gordon-Volkov wave functions, while the interaction of the hydrogen atom with the laser field is treated in second-order perturbation theory. Within this formalism, a closed analytical solution is derived for the nonlinear differential cross section, which is valid for circular as well linear polarizations. Simple analytical expressions of differential cross section are derived in the weak field domain for two-color laser field that is a combination of the fundamental and its second or third harmonics. It is shown that the nonlinear differential cross sections depend on the dynamical phase of the scattering process and on the helicities of the two-color circularly polarized laser field. A comparison between the two-photon absorption scattering signal for two-color co- and counterrotating circularly polarized laser fields is made for even ($2\ensuremath{\omega}$) or odd ($3\ensuremath{\omega}$) harmonics, and the effect of the intensity ratio of the two-color laser field components is studied. We analyze the origin of the symmetries in the differential cross sections and we show that the modification of the photon helicity implies a change in the symmetries of the scattering signal.