Rotation of polarization of light propagating through a gas of molecular super-rotors

TL;DR

This study investigates the polarization rotation of light passing through a gas of super-rotor molecules, revealing a nonmonotonic time dependence linked to molecular angular momentum transfer and potential applications in gas diagnostics.

Contribution

It provides the first combined theoretical and experimental analysis of polarization drag in a gas of molecular super-rotors, highlighting its sensitivity to intermolecular interactions.

Findings

Observed nonmonotonic polarization rotation over time.

Demonstrated polarization drag as a diagnostic for intermolecular potentials.

Linked angular momentum transfer to gas flow and vortex formation.

Abstract

We present a detailed theoretical and experimental study of the rotation of the plane of polarization of light traveling through a gas of fast-spinning molecules. This effect is similar to the polarization drag phenomenon predicted by Fermi a century ago and it is a mechanical analog of the Faraday effect. In our experiments, molecules were spun up by an optical centrifuge and brought to the super-rotor state that retains its rotation for a relatively long time. Polarizability properties of fast-rotating molecules were analyzed considering the rotational Doppler effect and Coriolis forces. We used molecular dynamics simulations to account for intermolecular collisions. We found, both experimentally and theoretically, a nontrivial nonmonotonic time dependence of the polarization rotation angle. This time dependence reflects transfer of the angular momentum from rotating molecules to the macroscopic gas flow, which may lead to the birth of gas vortices. Moreover, we show that the long-term behavior of the polarization rotation is sensitive to the details of the intermolecular potential. Thus, the polarization drag effect appears as a novel diagnostic tool for the characterization of intermolecular interaction potentials and studies of collisional processes in gases.