We investigate strong-field ionization of linear molecules by a two-color laser field of frequencies rω and sω having coplanar counterrotating or corotating elliptically polarized components (ω is the fundamental laser field frequency and r and s are integers). Using the improved molecular strong-field approximation we analyze direct above-threshold ionization (ATI) and high-order ATI (HATI) spectra. More precisely, reflection and rotational symmetries of these spectra for linear molecules aligned in the laser-field polarization plane are considered. The reflection symmetries for particular molecular orientations, known to be valid for a bicircular field (this is the field with circularly polarized counterrotating components), are valid also for arbitrary component ellipticities. However, specific rotational symmetries that are satisfied for HATI by a bicircular field, are violated for an arbitrary elliptically polarized field with counterrotating components. For the corotating case and the N2 molecule we analyze molecular-orientation-dependent interferences and plateau structures for various ellipticities.

Electron-ion radiative recombination assisted by a bichromatic (two-component) elliptically polarized laser field is analyzed in the frame of the $S\text{-matrix}$ theory. The second Born approximation is applied in the expansion of the $S\text{-matrix}$ element where the first term in the expansion corresponds to the direct recombination of electrons with ionic targets, while the second term corresponds to the recombination preceded by an electron-ion scattering. The latter process is possible in the presence of a laser field. If the electron scatters on an ionic target, it may be subsequently driven back by the laser field and recombine with the same ion. The photon emitted in this process may have a high energy. We have studied the dependence of the energy spectrum on various laser-field and incident electron parameters. The energy spectra obtained show plateaulike structures with abrupt cutoffs. These cutoffs are explained by a classical analysis.

Nonlinear quantum-mechanical phenomena in strong laser fields, such as high-order harmonic generation (HHG) and above-threshold ionization (ATI) are significantly modified if the applied laser field is bichromatic and/or elliptically polarized. Numerical results obtained within the strong-field approximation are presented for two special cases. We show results for HHG by plasma ablation in a bichromatic linearly polarized laser field. We also consider the ATI process in bicircular field which consists of two coplanar counter-rotating circularly polarized fields.