Molecular movie of ultrafast coherent rotational dynamics

TL;DR

This paper demonstrates the direct recording of high-resolution molecular movies capturing ultrafast rotational dynamics of molecules, revealing detailed quantum behavior and surpassing previous alignment limits.

Contribution

It introduces a novel experimental approach combining quantum-state selection and optimized pulse sequences to achieve unprecedented field-free molecular alignment.

Findings

Achieved a high degree of molecular alignment exceeding theoretical single-pulse limits.

Reconstructed the full quantum rotational wavepacket from experimental data.

Validated the quantum dynamics through solutions of the time-dependent Schrödinger equation.

Abstract

Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. We present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single-quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, $\langle \cos^{2}{\theta_{2D}}\rangle=0.96$ ($\langle \cos^{2}{\theta}\rangle=0.94$) was achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schr\"odinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalised the observed very high degree of alignment.