Dynamic interference minimum affected by permanent dipole in high-harmonic generation from CO molecules

We investigate the high-harmonic generation from CO molecules subjected to intense few-cycle laser fields by numerically solving the time-dependent Hartree-Fock equations. A dynamic minimum due to the interference of the HOMO and HOMO-2 orbitals is observed in the harmonic spectrum and further studies reveal that the HOMO-1 orbital plays an indispensable role in the formation of the minimum. Because the HOMO-1 orbital has a permanent dipole moment, it affects the coupling between HOMO and HOMO-2 orbitals during the time evolution, which can modify the phase difference between harmonic emission of HOMO and HOMO-2 orbitals in the propagation and recombination processes and relative contributions from two orbitals to the harmonic spectrum. This work sheds new insight into the study of multi-orbital effect in high-harmonic generation from polar molecules.