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

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. Herein, we consider the effects of state-dependent alignment in estimating the optical dipole force acting on the molecules 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

Scattering of adiabatically aligned molecules by nonresonant optical standing waves

“…On the other hand, at the higher rotational temperature of T rot = 35 K, the two corresponding simulation results are almost identical and agree well with the measurements (Fig. 5C), thereby confirming previous experimental results (22) and theoretical predictions (23) quantitatively. The agreement also validates the determination of <v 0x >.…”

“…Nonetheless, state-dependent alignment was not considered in these experiments. A subsequent theoretical study predicted that scattering of CS 2 molecules at T rot ~ 1 K by an optical standing wave would exhibit strong state-dependent alignment effects on the molecular trajectories (23). The present study experimentally confirms this theoretical prediction.…”

“…To investigate the alignment effect, we use rotationally cold molecules (T rot ~ 1 K) occupying only a few rotational states. Control experiments are performed with molecules at T rot ~ 35 K, where the alignment effect is predicted to be averaged out (23). The molecular beam of T rot ~ 1 or 35 K is transversely dispersed by the optical standing wave.…”