High harmonic generation for N2 and CO2 beyond the two-point model

Strong field high harmonic generation ( HHG) can reveal the quantum structure of the source molecule. We calculate the effect of interference between the recombining photoelectron and the orbital from which it was field ionized in the single- active- electron standard picture of HHG in N-2 and CO2. We compare our results for the highest occupied molecular orbitals ( HOMO's) to the predictions of a popular two- point scattering model. For N2, we find an agreement for very large internuclear separations and no agreement for the ground- state internuclear distance. We reduce the arguments to the Fourier transform of the HOMO, which depends on the internuclear separation. For CO2, we distinguish between two geometries. For one of these, we find a perfect agreement with the two- point scattering model; however, the emitted radiation is not phase matched in this case. The experimentally accessible radiation does not agree with the simple model.