Generation and properties of elliptically polarized high-order harmonics from CO$_2$ driven by symmetry-broken two-color fields

Abstract Elliptically polarized high-order harmonics have attracted considerable attention due to their important applications in probing matter chirality and magnetic circular dichroism. Here, we propose a scheme for generating elliptically polarized high-order harmonics from CO$_2$ molecules driven by a two-dimensional asymmetric laser field. Owing to the intrinsic asymmetry of the driving field, the harmonics emitted at each molecular alignment angle exhibit nonzero ellipticity and share the same helicity, enabling the generation of elliptically polarized harmonics from unaligned molecules. Moreover, harmonics with relatively large ellipticity can be obtained by tuning the ellipticity of the fundamental field, while the harmonic ellipticity can be further manipulated by adjusting the relative phase of the two-color fields. This scheme provides a simple and robust approach for generating elliptically polarized high-order harmonics with tunable polarization properties.