Characterizing gas flow from aerosol particle injectors

TL;DR

This paper introduces a laser-based imaging technique to measure and characterize gas flow from aerosol particle injectors with high spatial resolution, aiding optimization in single-particle imaging experiments at free-electron lasers.

Contribution

A novel laser-induced plasma imaging method for precise measurement of gas densities from aerosol injectors in vacuum environments.

Findings

Detected helium densities as low as 4×10^{16} cm^{-3}

Achieved micrometer spatial resolution in gas density imaging

Estimated low background scattering signals for imaging experiments

Abstract

A novel methodology for measuring gas flow from small orifices or nozzles into vacuum is presented. It utilizes a high-intensity femtosecond laser pulse to create a plasma within the gas plume produced by the nozzle, which is imaged by a microscope. Calibration of the imaging system allows for the extraction of absolute number densities. We show detection down to helium densities of $4\times10^{16}$~cm$^{-3}$ with a spatial resolution of a few micrometer. The technique is used to characterize the gas flow from a convergent-nozzle aerosol injector [Struct.\ Dyn.~2, 041717 (2015)] as used in single-particle diffractive imaging experiments at free-electron laser sources. Based on the measured gas-density profile we estimate the scattering background signal under typical operating conditions of single-particle imaging experiments and estimate that fewer than 50 photons per shot can be expected on the detector.