XPP: X-ray Pump Probe

The XPP hutch is a versatile machine that can work with many types of samples.

The hutch has the same type of robotic arm that’s used to assemble cars in factories. The arm moves the XPP detector to get the best angle for viewing a particular sample.

XPP is used to create molecular movies. One movie featured 1,3-cyclohexadiene, a ring-shaped molecule that serves as a model for studying what happens when sunlight hits our skin and triggers the synthesis of vitamin D. In the experiments, laser light hit the molecule and broke open its ring, while X-rays made snapshots of the ultrafast movements of the atoms. Those snapshots were compiled into a molecular movie of the ring opening.

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The XPP (X-ray Pump Probe) instrument predominantly uses a fast optical laser to generate transient states of matter, which are probed with hard X-ray pulses from LCLS. This reveals changes in the sample’s structure initiated by the laser excitation.