High Harmonic Generation in Polar Molecules: Insights from TDDFT Calculations

This study examines the high harmonic spectra of molecules lacking inversion symmetry. The even-to-odd intensity ratios depend on the molecular orientation relative to the laser polarization. The even harmonics diminish as the orientation shifts away from parallel. Their polarization also deviates from that of the laser. The influence of laser parameters on the orientation dependence is minimal. For HCN, the contribution of different orbitals dominates each half-optical cycle. Among the plateau harmonics, the interference of the orbital contributions is destructive in a range of odd harmonics and constructive for the even ones, leading to varied even-odd intensity ratios and a minimum of odd harmonics at 22 eV.