Observing Molecular Spinning via the Rotational Doppler Effect

TL;DR

This paper demonstrates the observation of the rotational Doppler shift caused by coherently spinning molecules, providing explicit evidence of unidirectional molecular rotation and enabling new measurement techniques.

Contribution

It introduces a novel method to generate and measure large rotational Doppler shifts using coherently spinning molecules, advancing molecular rotation control and detection.

Findings

Measured RDS orders of magnitude greater than previous methods

Provided explicit evidence of unidirectional molecular rotation

Enabled potential for monitoring and controlling molecular rotational direction

Abstract

When circularly polarized light is scattered from a rotating target, a rotational Doppler shift (RDS) emerges from an exchange of angular momentum between the spinning object and the electromagnetic field. Here, we used coherently spinning molecules to generate a shift of the frequency of a circularly polarized probe propagating through a gaseous sample. We used a linearly polarized laser pulse to align the molecules, followed by a second delayed pulse polarized at 45{\deg} to achieve unidirectional molecular rotation. The measured RDS is orders of magnitude greater than previously observed by other methods. This experiment provides explicit evidence of unidirectional molecular rotation and paves the way for a new class of measurements in which the rotational direction of molecular reagents may be monitored or actively controlled.