Field-free molecular orientation by two-color shaped laser pulse together with time-delayed THz laser pulse

Abstract

We theoretically investigate field-free molecular orientation by using an off-resonant two-color shaped laser pulse with a slow turn-on and rapid turn-off and a time-delayed THz laser pulse. It is shown that the molecular orientation can be greatly enhanced by applying this scheme compared to the two-color shaped or THz laser pulse alone. We discuss the effects of the rise time and the electric field amplitude of the two-color shaped laser pulse on molecular orientation, and demonstrate that effective molecular orientation can be achieved by a moderate intensity laser pulse with a short rise time. Furthermore, by changing the delay time between the two-color shaped laser pulse and the THz laser pulse and the carrier envelope phase of the THz laser pulse, the molecular orientation can be enhanced or lowered to some degree.

Controlling molecular orientation by laser pulses with two different envelope shapes

“…When the LiH molecule is exposed to the linearly polarized laser pulse, the permanent dipole moment or polarizability and hyperpolarizability of the molecule interact with the laser field, generating molecular orientation. The degree of molecular orientation is calculated by [55] cosθ…”

“…We only consider the rotational excitation of the molecule and ignore the vibrational excitation of the molecule. Thus, the molecular Hamiltonian within rigid-rotor approximation is written as [55] b…”

Influence factor analysis of field-free molecular orientation

“…In the rigid rotor approximation, the total Hamiltonian of the molecule interacting with the combination of two-color laser pulse and THz laser pulse is given by [38]…”

Quantum control of field-free molecular orientation

“…76 Subsequent works have further improved upon this enhancement by incorporating additional pre-alignment pulses or optimizing the parameters of the pulses. 122–124 Experimental demonstrations of this hybrid scheme have demonstrated its capability to induce transient field-free orientation of OCS molecules at low temperatures around 2 K, as well as the rotational dynamics of asymmetric molecules at ambient temperatures. 74 Moreover, a recent experiment has revealed that this scheme can significantly increase the orientation of iodomethane molecules at room temperature, surpassing the levels achieved by employing pure terahertz pulses alone.…”