Abstract
Imaging biological molecules in the gas-phase requires novel sample delivery methods, which generally have to be characterized and optimized to produce high-density particle beams. A non-destructive characterization method of the transverse particle beam profile is presented. It enables the characterization of the particle beam in parallel to the collection of, for instance, x-ray-diffraction patterns. As a rather simple experimental method, it requires the generation of a small laser-light sheet using a cylindrical telescope and a microscope. The working principle of this technique was demonstrated for the characterization of the fluid-dynamic-focusing behavior of 220 nm polystyrene beads as prototypical nanoparticles. The particle flux was determined and the velocity distribution was calibrated using Mie-scattering calculations.
Highlights
Knowledge of the structure of biological molecules, such as proteins or viruses, is fundamental for understanding their function
In order to achieve this within the limited amount of time available at central x-ray free-electrons lasers (XFELs) facilities, requires a high particle flux in the gas-phase
An example of a measured full particle beam profile is shown in Figure 2 b, recorded 6 mm below the aerodynamic lens stacks (ALS) injector
Summary
Knowledge of the structure of biological molecules, such as proteins or viruses, is fundamental for understanding their function. As the samples investigated get smaller in size, approaching the limit of single proteins, the necessary x-ray intensity for recording a single-shot diffraction pattern increases. This higher intensity is typically achieved by focusing the x-ray beam to a smaller spot, in the most extreme cases to sizes of only ∼100 nm. This places stringent demands on the employed sample delivery methods, typically aerodynamic lens stacks (ALS) [5,6,7], and requires their characterization and optimization prior to XFEL experiments with laboratory-based methods
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