Controlled molecule injector for cold, dense, and pure molecular beams at the European x-ray free-electron laser

TL;DR

The paper introduces a new controlled molecule injector (COMO) for the EuXFEL that produces cold, dense, and pure molecular beams, enabling precise studies of molecules and clusters with x-ray free-electron lasers.

Contribution

A novel, versatile molecular-beam injection setup (COMO) with electrostatic deflector and cold source, designed for integration at EuXFEL instruments for high-precision molecular studies.

Findings

Produced rotationally cold ($T\,\approx1$ K) molecular beams with high density.

Demonstrated successful operation with optical and x-ray lasers.

Enabled controlled, pure, and size-selected molecular samples for XFEL experiments.

Abstract

A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A $b$-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold ($T\approx1$~K) and dense ($\rho\approx10^8$~cm$^{-3}$) molecular beam with pulse durations up to 100~\us generated by a new version of the Even-Lavie valve. Here, a performance overview of the COMO setup is presented along with characterization experiments performed both, with an optical laser at the Center for Free-Electron-Laser Science and with x-rays at EuXFEL under burst-mode operation. COMO was designed to be attached to different instruments at the EuXFEL, in particular at the small quantum systems (SQS) and single particles, clusters, and biomolecules (SPB) instruments. This advanced controlled-molecules injection setup enables XFEL studies using highly defined samples with soft and hard x-ray FEL radiation for applications ranging from atomic, molecular, and cluster physics to elementary processes in chemistry and biology.