Ellipticity Of Odd-Even Harmonics From Oriented Asymmetric Molecules In Strong Linearly Polarized Laser Fields

In the strong laser field, the high-order harmonic generation(HHG) from atoms and molecules has been one of the most intensely studied aspects of strong field physics. The reason is that the study of HHG from atoms and molecules has very wide application, that is due to: 1) It can be applied as a coherent radiation source in the extreme ultraviolet(XUV) and soft x-ray regions. 2) It can be used to molecular orbital tomography. 3) The study on the HHG greatly improves the theory of the strong field physics. Previous studies on HHG mainly focus on the power spectra of the harmonics emitted along the laser polarization(i.e.,the parallel harmonics).. As this polarization of HHG is closely related to not only the parallel harmonics and the harmonics emitted perpendicular to the laser polarization(i.e., the perpendicular harmonics) but also the phase of the harmonics, it provides other deep insights into the mechanism of the molecular HHG.In this paper, through the numerical solution of the time-dependent schrodinger&& equation(TDSE) in three dimensions(3D), we study the properties of the polarization of odd-even harmonics from asymmetric model 2He H+molecules with different orientation angles and molecular parameters in strong linearly polarized laser fields in detail. 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 dependence 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.