Controlling molecular orientation by laser pulses with two different envelope shapes

Abstract

We use density matrix theory to numerically simulate the orientation of LiH molecules induced by laser pulses with two different envelope shapes. The results show that the envelope shape of the terahertz single-cycle laser pulse (SCP) has significant effects on molecular orientation degree and duration. When a SCP with adjusted laser field amplitude and carrier envelope phase is used to steer the molecular orientation, a larger orientation degree can be obtained by the Gaussian-shaped SCP, while a longer orientation duration can be realized by the sin 2 -shaped SCP.When combined with the two-color femtosecond laser pulse, the sin 2 -shaped SCP is better than Gaussian-shaped SCP, either in improving orientation degree and duration or in stability and controllability shown with increasing temperature. The optimal molecular orientation can be realized under the combination of the two-color femtosecond laser pulse and sin 2 -shaped SCP which has the appropriate delay time: the maximal orientation degree reaches 0.801 at 0 K and 0.450 at 20 K, the maximal orientation duration is 31.3% of the rotational period at 0 K.

Quantum control of field-free molecular orientation

“…The physical mechanism behind generating field-free molecular orientation involves the formation of a superposition of rotational states with even and odd angular momentum quantum numbers. Three basic approaches have been proposed, involving (1) intense nonresonant interactions of optical pulses with the polarizability and hyperpolarizability, 36,[46][47][48][49][50] (2) resonant interactions of terahertz pulses with the permanent dipole moment, [51][52][53][54] and (3) a combination of a strong nonresonant pulse and a terahertz pulse. [55][56][57] The first approach involves a two-color pure optical scheme for achieving all-optical molecular orientation.…”

Influence of molecular orientation on the photodissociation process of LiH molecules

“…LiH as a prototype diatomic molecule in molecular reaction dynamics has attracted considerable attention, leading to widespread investigations in recent years [1][2][3][4][5][6]. The ground state structure and potential energy function of LiH have been provided [7][8][9], and dedicated efforts have been devoted to manipulate both orientation and photodissociation process [10][11][12]. The LiH molecule is also an excellent hydrogen storage material, which has important applications in the development of new energy [13][14][15].…”