Influence of orbital symmetry on high-order-harmonic generation and quantum tomography

Quantum tomography based on high-order-harmonic generation in molecules is potentially a powerful technique to image electron orbitals. However, many assumptions are needed to reconstruct the spatial orbital structure from the harmonic spectrum. With two-dimensional model calculations, we examine several of these assumptions and find their validity depends strongly on the orbital symmetry and reconstruction axis. In fact, for certain symmetries we cannot find a reconstruction procedure that gives good results. We compare the length and velocity forms of the dipole interaction and find that the form of the dipole strongly affects the quality of the orbital reconstruction. For all of the wave functions studied, the velocity form works as well or better than the length form and may be the best method for quantum tomography. Moreover, in many cases, using the harmonic radiation polarized perpendicular to the molecular axis gives much better results than the parallel polarization. Finally, we examine the minima in the harmonic spectra as a function of angle and find that they cannot always be interpreted as a two-center interference effect.