Asymmetry in the harmonic generation from nonsymmetric molecules

Abstract

We report a calculation of the harmonic emission from a one-electron heteronuclear nonsymmetric molecule (HeH2+) interacting with a few-cycle laser pulse linearly polarized along the molecular axis. We find that a 180° rotation of the molecule (or equivalently a 180° change in the carrier-envelope phase) leads to substantial changes in the harmonic emission of the molecule. Phase-dependent plateaux and cutoffs appear in the harmonic spectrum as a consequence of the phase-dependent electric field of few-cycle pulses. Asymmetries in the intensity of harmonics result from the phase dependence of ionization rates in nonsymmetric molecules, and from the fact that depending on the molecular orientation, the ionized electron wavepacket can be Coulomb focused as it visits the proton twice before the recollision leading to harmonic generation.