Coherent radiative decay of molecular rotations: a comparative study of terahertz-oriented versus optically aligned molecular ensembles

TL;DR

This study compares the decay of rotational dynamics in molecules induced by optical alignment and terahertz orientation, highlighting the significant role of coherent radiative emission in the decay process.

Contribution

It provides experimental evidence that coherent radiative emission accelerates decay in oriented molecular ensembles, a phenomenon not observed in aligned ensembles.

Findings

Oriented ensembles decay faster than aligned ones.

Coherent radiative emission significantly contributes to decay.

Decay rates vary with molecular species and pressure.

Abstract

The decay of field-free rotational dynamics is experimentally studied in two complementary methods: laser-induced molecular alignment and terahertz-field-induced molecular orientation. Comparison between the decay rates of different molecular species at various gas pressures reveals that oriented molecular ensembles decay faster than aligned ensembles. The discrepancy in decay rates is attributed to the coherent radiation emitted by the transiently oriented ensembles and is absent from aligned molecules. The experimental results reveal the dramatic contribution of coherent radiative emission to the observed decay of rotational dynamics and underline a general phenomenon expected whenever field-free coherent dipole oscillations are induced.