Effect of rotational-state-dependent molecular alignment on the optical dipole force

TL;DR

This paper investigates how molecular alignment, dependent on quantum state, influences the optical dipole force, introducing an effective polarizability to improve force estimates in optical molecular manipulation.

Contribution

It explicitly incorporates molecular alignment effects into the calculation of the optical dipole force using an effective polarizability, enhancing accuracy over previous implicit methods.

Findings

Alignment-dependent polarizability improves force estimation accuracy.

Trajectory simulations show significant differences when including molecular alignment.

Method enables better state-selection techniques for nonpolar molecules.

Abstract

The properties of molecule-optical elements such as lenses or prisms based on the interaction of molecules with optical fields depend in a crucial way on the molecular quantum state and its alignment created by the optical field. However, in previous experimental studies, the effects of state-dependent alignment have never been included in estimates of the optical dipole force acting on the molecules while previous theoretical investigations took the state-dependent molecular alignment into account only implicitly. Herein, we consider the effects of molecular alignment explicitly and, to this end, introduce an effective polarizability which takes proper account of molecular alignment and is directly related to the alignment-dependent optical dipole force. We illustrate the significance of including molecular alignment in the optical dipole force by a trajectory study that compares previously used approximations with the present approach. The trajectory simulations were carried out for an ensemble of linear molecules subject to either propagating or standing-wave optical fields for a range of temperatures and laser intensities. The results demonstrate that the alignment-dependent effective polarizability can serve to provide correct estimates of the optical dipole force, on which a state-selection method applicable to nonpolar molecules could be based. We note that an analogous analysis of the forces acting on polar molecules subject to an inhomogeneous static electric field reveals a similarly strong dependence on molecular orientation.