Asymmetric spatial distribution in the high-order harmonic generation of a H2+ molecule controlled by the combination of a mid-infrared laser pulse and a terahertz field

The control of the spatial distribution in the high-order harmonic generation (HHG) of a H-2+ molecule is theoretically investigated by the combination of a mid-infrared laser pulse and a terahertz (THz) field. We use a THz pulse to steer the electron motion, and the numerical results show that the cutoff of the harmonic from the recombination of the electron with the nucleus along the negative-z direction is enhanced and the case along the positive-z direction is suppressed when a THz field is added. The underlying physical mechanism is illustrated by the semi-classical three step model and the ionization probability. The time-frequency analysis further demonstrates the asymmetric spatial distribution in a HHG controlled by adding a THz field.