Field-free orientation of 7LiH steered by a few-cycle nonlinearly chirped pulse

Abstract

We demonstrate theoretically that an efficient field-free molecular orientation of 7LiH molecule steered by a few-cycle nonlinearly chirped laser pulse with frequency in the terahertz regime can be achieved. The frequency modulation parameter β plays an important role in the molecular orientation, the maximum molecular orientation |〈cosθ〉|max is 0.848 and the orientation duration is 150 fs when β=7.25. In the range of electric-field peak intensity E0=[0.1,4.0] MV/cm, we can find the maximum orientation degree in both positive and negative directions. Compared to the scheme steered by a normal laser pulse, we can find that a more efficient molecular orientation and a smaller difference in population between the adjacent states can be realized by using the nonlinearly chirped laser pulse under the same near-single-period conditions. In addition, at the same temperature, a higher molecular orientation and a smaller decrease rate of orientation with temperature can be obtained by the nonlinearly chirped laser pulse.