High-order harmonic generation from two-center molecules: Time-profile analysis of nuclear contributions

We solve the exact three-dimensional time-dependent Schrodinger equation for H-2(+) (with fixed nuclei) interacting with an intense laser pulse with an arbitrary oriented linear polarization. We find that at equilibrium internuclear distance, the ionization probability of H-2(+) is maximum for the parallel orientation of the molecule with respect to the laser polarization, and is minimum for the perpendicular orientation. The contribution of each nucleus to the harmonic spectrum is evaluated, so that interference effects between the two contributions are assessed unambiguously. We show that every half-cycle, high order harmonics are emitted by each nucleus when the electron wave packet returns for a recollision with both nuclei, and that the resulting harmonic emission is predominant for the nucleus that experiences the first recollision. In general, each nucleus emits both even and odd harmonics, but even harmonics are destroyed by interferences between contributions from each nucleus. In general, this destructive interference occurs over a large spread of harmonic orders, which depends on the angle between the molecular axis and the laser polarization.