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We describe a liquid jet injector system developed to deliver fully solvated microscopic target species into a probe beam under either vacuum or ambient conditions. The injector was designed specifically for x-ray scattering studies of biological nanospecies using x-ray free electron lasers and third generation synchrotrons, but is of interest to any application in which microscopic samples must be delivered in a fully solvated state and with microscopic precision. By utilizing a gas dynamic virtual nozzle (GDVN) to generate a sample-containing liquid jet of diameter ranging from 300 nm to 20 μm, the injector avoids the clogging problems associated in this size range with conventional Rayleigh jets. A differential pumping system incorporated into the injector shields the experimental chamber from the gas load of the GDVN, making the injector compatible with high vacuum systems. The injector houses a fiber-optically coupled pump laser to illuminate the jet for pump-probe experiments and a hermetically sealed microscope to observe the liquid jet for diagnostics and alignment during operation. This injector system has now been used during several experimental runs at the Linac Coherent Light Source. Recent refinements in GDVN design are also presented.

We consider a monodispersed Rayleigh droplet beam of water droplets doped with proteins. An intense infrared laser is used to align these droplets. The arrangement has been proposed for electron- and x-ray-diffraction studies of proteins which are difficult to crystallize. This paper considers the effect of thermal fluctuations on the angular spread of alignment in thermal equilibrium, and relaxation phenomena, particularly the damping of oscillations excited as the molecules enter the field. The possibility of adiabatic alignment is also considered. We find that damping times in a high-pressure gas cell as used in x-ray-diffraction experiments are short compared with the time taken for molecules to traverse the beam and that a suitably shaped field might be used for electron-diffraction experiments in vacuum to provide adiabatic alignment, thus obviating the need for a damping gas cell.