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The Coherent X-Ray Imaging (CXI) instrument makes use of the unique brilliant hard X-ray pulses from LCLS to perform a wide variety of experiments utilizing various techniques. The primary capability of CXI is to make use of the high peak power of the focused x-ray beam using the “diffraction-before-destruction” method. This technique prevents damage to a sample during the measurement by performing the measurement faster than the damage or destruction process with ultrashort pulses. This is particular advantageous for biological samples that suffer from electronic and structural damage during long continuous exposures to x-rays.
While designed originally to image single sub-micron particles using Coherent Diffractive Imaging (CXI) techniques, the CXI instrument consists of a highly flexible instrumentation suite to make use of hard x-rays primarily in a vacuum sample environment. It is available for Serial Femtosecond Crystallography (SFX) measurements capable of determining the structure of biomolecules using nanocrystals. It is also suitable for any forward scattering experiment requiring or benefiting from a vacuum sample environment. A variety of tools and devices have been developed that allow CXI to make use of other techniques such as X-ray Emission Spectroscopy, back-scattering, small and wide angle scattering, ion and electron time of flight spectroscopy. A flexible pump laser system is available for time-resolved experiments in the femtosecond time scale. CXI is available for any scientific field requiring use of the LCLS beam, including structural biology, material science, materials in extreme conditions, atomic molecular and optical physics, chemistry, soft condensed matter and high field x-ray science. Samples can be introduced to the x-ray beam either fixed on targets or using a particle injector that can deliver free-standing particles or samples in a liquid jet to the beam. Experiments at atmospheric pressure are possible under certain limited circumstances. High quality focusing optics are available to generate three foci (10, 1 and 0.1 micron). The CXI instrument operates primarily in the 5-11 keV range with capabilities for operation under reduced performance above 11 keV with use of the harmonics of the beam.
The near complete transverse coherence of the LCLS beam is ideal for experiment requiring a coherent beam and could allow single particles to be imaged at high resolution while the short pulse duration will limit radiation damage during the measurement.
SLAC National Accelerator Laboratory, Menlo Park, CA
Operated by Stanford University for the U.S. Dept. of Energy