Orientation-resolved Cooper-like minimum in high-order harmonic spectrum from asymmetric molecules

We present the observation of an orientation-resolved Cooper-like minimum in the high-order harmonic spectrum from an asymmetric CO molecule employing the time-dependent density functional theory. By applying a linearly polarized field, we find that obvious minimum contributed by HOMO can be observed in the pure even harmonics with the polarization perpendicular to the laser polarization when the molecular axis is perpendicular to the laser polarization. By contrast, when the molecular axis is along to the laser polarization, a minimum can be identified from odd harmonics, but its position is slightly moved with the pulse intensities and wavelengths partly due to the interference between HOMO and HOMO-2. These findings reinforce the current understanding of cooper-like minimum in HHG from asymmetric molecules, providing a way to observe such minimum in asymmetric molecules for experiments by using the laser field with laser polarization perpendicular to the molecular axis and observing the HHG component with the polarization perpendicular to the laser polarization.