Optical imaging of coherent molecular rotors

TL;DR

This paper introduces a novel non-destructive optical imaging technique to visualize and record real-time coherent rotational dynamics of molecules in a gas, enabling new insights into ultrafast molecular processes.

Contribution

The work presents a new optical method for direct visualization of molecular rotation dynamics, using polarization imaging, which is non-destructive and applicable to various rotational phenomena.

Findings

Successfully visualized alignment-antialignment cycles.

Demonstrated unidirectional molecular rotation imaging.

Potential to study ultrafast chemical transformations.

Abstract

Short laser pulses are widely used for controlling molecular rotational degrees of freedom and inducing molecular alignment, orientation, unidirectional rotation and other types of coherent rotational motion. To follow the ultra-fast rotational dynamics in real time, several techniques for producing molecular movies have been proposed based on the Coulomb explosion of rotating molecules, or recovering molecular orientation from the angular distribution of high-harmonics. The present work offers and demonstrates a novel non-destructive optical method for direct visualization and recording of movies of coherent rotational dynamics in a molecular gas. The technique is based on imaging the time-dependent polarization dynamics of a probe light propagating through a gas of coherently rotating molecules. The probe pulse continues through a radial polarizer, and is then recorded by a camera. We illustrate the technique by implementing it with two examples of time-resolved rotational dynamics: alignment-antialignment cycles in a molecular gas excited by a single linearly polarized laser pulse, and unidirectional molecular rotation induced by a pulse with twisted polarization. This method may open new avenues in studies on fast chemical transformation phenomena and ultrafast molecular dynamics caused by strong laser fields of various complexities.