Delivering sub-micrometer particles to an intense x-ray focus is a crucial
aspect of single-particle diffractive-imaging experiments at x-ray
free-electron lasers. Enabling direct visualization of sub-micrometer aerosol
particle streams without interfering with the operation of the particle
injector can greatly improve the overall efficiency of single-particle imaging
experiments by reducing the amount of time and sample consumed during
measurements. We have developed in-situ non-destructive imaging diagnostics to
aid real-time particle injector optimization and x-ray/particle-beam alignment,
based on laser illumination schemes and fast imaging detectors. Our diagnostics
are constructed to provide a non-invasive rapid feedback on injector
performance during measurements, and have been demonstrated during diffraction
measurements at the FLASH free-electron laser.Comment: 15 page
