High-order harmonic generation from diatomic molecules in an orthogonally polarized two-color laser field

We study high-order harmonic generation (HHG) from aligned H2+ and oriented HeH2+ and HeH+ molecular ions in orthogonally polarized two-color laser pulses composed of an intense fundamental field and a time-delayed weak second-harmonic field. By numerical solution of the time-dependent Schrödinger equation, we find that for a fixed alignment angle, as the delay between the two colors varies on a subcycle scale, the HHG intensity from H2+ shows a pronounced groove in a specific delay region, which turns out to be a two-center interference effect. HHG from asymmetric molecules shows an obvious orientation dependence where the interference effect can be observed only when the tunneling occurs on the helium side. The physical origin of these phenomena is deduced by modeling the two-color HHG intensity of H2+ using classical and quantum models and by modeling that of asymmetric molecules with the help of field-free collisions of Gaussian wave packets with the core.