# Acoustic funnel and buncher for nanoparticle injection

## TL;DR

This paper proposes an acoustic method to focus and bunch nanoparticle beams, improving synchronization with x-ray pulses in XFEL experiments, potentially reducing data collection times significantly.

## Contribution

It introduces a simple, mechanically based acoustic technique for nanoparticle manipulation that can be integrated into existing XFEL setups, enhancing particle beam control.

## Key findings

- Achieved sub-micrometer transverse focusing of nanoparticles.
- Demonstrated bunching of particles at x-ray pulse repetition rates.
- Potential to reduce data collection times by a factor of 10,000.

## Abstract

Acoustics-based techniques are investigated to focus and bunch nanoparticle beams. This allows to overcome the prominent problem of the longitudinal and transverse mismatch of particle stream and x-ray beam in single-particle/single molecule imaging at x-ray free-electron lasers (XFEL). It will also enable synchronised injection of particle streams at kHz repetition rates. Transverse focusing concentrates the particle flux to the (sub)micrometer x-ray focus. In the longitudinal direction, focused acoustic waves can be used to bunch the particle to the same repetition rate as the x-ray pulses. The acoustic manipulation is based on simple mechanical recoil effects and could be advantageous over light-pressure-based methods, which rely on absorption. The acoustic equipment is easy to implement and can be conveniently inserted into current XFEL endstations. With the proposed method, data collection times could be reduced by a factor of $10^4$. This work does not just provide an efficient method for acoustic manipulation of streams of arbitrary gas phase particles, but also opens up wide avenues for acoustics-based particle optics.