Long-lasting field-free alignment of large molecules inside helium nanodroplets

TL;DR

This paper demonstrates long-lasting, field-free alignment of large molecules within helium nanodroplets, enabling advanced molecular imaging and dynamics studies without external field perturbations.

Contribution

It introduces a novel method for achieving sustained, field-free molecular alignment in large molecules using helium nanodroplets, extending capabilities beyond small molecules.

Findings

Achieved tens of picoseconds of field-free alignment of large molecules.

Demonstrated alignment-dependent strong-field ionization measurements.

Enabled potential for ultrafast molecular dynamics experiments.

Abstract

Molecules with their axes sharply confined in space, available through laser-induced alignment methods, are essential for many current experiments, including ultrafast molecular imaging. Most of these applications require both that the aligning laser field is turned-off, to avoid undesired perturbations, and that the molecules remain aligned sufficiently long that reactions and dynamics can be mapped out. Presently, this is only possible for small, linear molecules and for times less than 1 picosecond. Here, we demonstrate strong, field-free alignment of large molecules inside helium nanodroplets, lasting tens of picoseconds. Molecular alignment in either one or three dimensions is created by a slowly switched-on laser pulse, made field-free through rapid pulse truncation, and retained thanks to the impeding effect of the helium environment on molecular rotation. We illustrate the opportunities that field-free aligned molecules open by measuring the alignment-dependent strong-field ionization yield of a thiophene oligomer. Our technique will enable molecular-frame experiments, including ultrafast excited state dynamics, on a variety of large molecules and complexes.