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.
Highlights
Current laser technology has made it possible to generate spatially and temporally well-defined optical fields—whether propagating or standing wave—that can be used to manipulate molecular motion and create molecule-optical elements, such as lenses [1,2,3] and prisms [4,5], as well as to decelerate molecules [6,7,8,9,10,11]
We examine the counterpart of this effective polarizability that arises in the context of the dipole force exerted on polar molecules by an inhomogeneous static electric field
We have studied how state-dependent molecular alignment induced by two kinds of laser fields affects the molecular interaction potential, the optical dipole force, and the resulting velocity distribution as obtained by trajectory simulations
Summary
Current laser technology has made it possible to generate spatially and temporally well-defined optical fields—whether propagating or standing wave—that can be used to manipulate molecular motion and create molecule-optical elements, such as lenses [1,2,3] and prisms [4,5], as well as to decelerate molecules [6,7,8,9,10,11]. Translational motion of molecules subject to propagating laser fields was traced with quantum-mechanical [17], hybrid quantum-classical [17,18,19], and classical [20] trajectory methods, in which the state-dependent molecular alignment was included in the Hamiltonian of the system under study. The trajectories were calculated without considering the relation between the molecular alignment and the optical dipole force These studies focused on the low-intensity [20,21] or the high-intensity limits [17,18,19,20], wherein the molecules are hardly aligned or the degree of their alignment approaches its maximum, respectively. We examine the counterpart of this effective polarizability that arises in the context of the dipole force exerted on polar molecules by an inhomogeneous static electric field
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