High-order harmonic generation by molecules of discrete rotational symmetry interacting with circularly polarized laser field

The dynamics of harmonic generation by a molecule of discrete rotational symmetry oriented in the polarization plane of a circularly polarized laser field is discussed. A simple model system is presented and the corresponding high-order harmonic generation spectrum is calculated analytically as a sum of the bound-bound and the bound-continuum contributions. It is shown that, contrary to the case of rare gas atoms interacting with linearly polarized radiation, the dominant contribution to high-order harmonic generation by the studied class of systems comes from the bound-bound transitions. As a consequence, the mechanism of the process is different from the well-known rescattering mechanism due to Corkum and Kulander. At intensities high enough the molecular harmonic generation spectra reproduce the main features of the atomic ones, i.e., the plateau and the cutoff. Unlike the cutoff in the atomic case, the molecular cutoff position depends linearly on the electric field strength and the molecular dimensions. This should allow one to reach higher harmonic orders by employing larger molecular targets.