Ellipticity of odd-even harmonics from oriented asymmetric molecules in strong linearly polarized laser fields

We investigate the polarization of odd versus even high-order-harmonic generation (HHG) from oriented asymmetric molecules exposed to a strong and linearly polarized laser field. Our numerical simulations show that the properties of polarization of harmonics at diverse orientation angles differ significantly from each other. In particular, odd and even harmonics show different angle dependences of ellipticity. Our analyses reveal that the interplay of intramolecular interference and the contributions of different HHG routes plays an important role in the ellipticity of odd-even harmonics. In addition, the excited states also have nontrivial influence on this ellipticity. While the minimum arising from two-center interference is not easy to identify in the odd-even HHG spectra of asymmetric molecules, we show that the ellipticity of harmonics can be used as a sensitive tool to probe the position of the minimum, which is important in asymmetric molecular orbital imaging.