Effect of ionization asymmetry on high harmonic generation from oriented CO in orthogonal two-color fields

Abstract

We investigate the high harmonic generation from oriented CO molecules in orthogonal two-color (OTC) fields by solving the three-dimensional time-dependent Hartree–Fock equation. The infrared fundamental laser pulse with frequency ω polarized along the molecular axis drives the harmonic generation process, while a weak second harmonic field with frequency ω 1 = 2ω perturbs the electron dynamics along the direction perpendicular to molecular axis. We observe non-integer order harmonics of ω 1 generated from CO with its polarization perpendicular to the molecular axis, which differs from aligned H2 under the same laser fields. Combining the Lewenstein model with the classical electronic trajectory analysis, we find the ionization asymmetry along molecular axis in polar molecules under the cross modulation of the OTC fields results in the difference of high harmonics between CO and H2.