The influence of carrier envelope phase of single-cycle THz pulse on field-free orientation of NaI molecules

The influence of the carrier envelope phase (CEP) on the field-free orientation of the NaI molecule is investigated theoretically. The molecular orientation steered by a single-cycle terahertz (THz) pulse is studied by solving exactly the time-dependent Schrodinger equation including the rovibrational degrees of freedom. We find that the field-free orientation is dependent on the central frequency and CEP of the single-cycle pulse. The CEP of single-cycle THz pulse affects the field-free orientation mainly via changing the population distributions of rotational states. By choosing the CEP of single-cycle THz pulse at the appropriate central frequency, the maximum value of the degree of field-free orientation, ⟨cos θ ⟩, can reach 0.80. Moreover, we find that the duration of effective orientation (|⟨cos θ ⟩| ≥ 0.5) is relatively long in certain regions of the laser central frequency and the CEP.