Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
Results of coherent diffractive imaging experiments performed with soft X-rays (1-2 keV) at the Linac Coherent
Light Source are presented. Both organic and inorganic nano-sized objects were injected into the XFEL beam
as an aerosol focused with an aerodynamic lens. The high intensity and femtosecond duration of X-ray pulses
produced by the Linac Coherent Light Source allow structural information to be recorded by X-ray diffraction
before the particle is destroyed. Images were formed by using iterative methods to phase single shot diffraction
patterns. Strategies for improving the reconstruction methods have been developed. This technique opens
up exciting opportunities for biological imaging, allowing structure determination without freezing, staining or
Diffraction from the individual molecules of a molecular beam, aligned parallel to a single axis by a strong electric field
or other means, has been proposed as a means of structure determination of individual molecules. As in fiber diffraction,
all the information extractable is contained in a diffraction pattern from incidence of the diffracting beam normal to the
molecular alignment axis. We present two methods of structure solution for this case. One is based on the iterative
projection algorithms for phase retrieval applied to the coefficients of the cylindrical harmonic expansion of the
molecular electron density. Another is the holographic approach utilizing presence of the strongly scattering reference
atom for a specific molecule.
We have designed and commissioned an apparatus for serial crystallography of hydrated proteins at the Advanced Light
Source. Serial crystallography is a recently proposed method of imaging uncrystallized proteins at a third generation
synchrotron source. This paper describes the design of the apparatus and results from the first experiment, which
recorded x-ray diffraction patterns from 8 micron droplets containing photosystem 1 protein molecules.