XPP Science Goals

Biological, chemical, and physical processes involve the time-dependent transformation of matter on the atomic scale. Examples of these processes with technological and environmental significance are the photosynthetic generation of chemical energy, the catalytic production of fertilizer, the chemical degradation of pollutants, and the melting of ice. These structural transformations involve the motion of electrons, atoms, and molecules over very short distances (10^-9 m) and very short time scales (10^-12 s). Though much has been learned about these dynamical processes from previous work, particularly studies using X-rays and optical lasers, no existing technology can provide direct observation of atomic motions on ultrafast time scales.

The LCLS provides transversely-coherent hard X-rays with unprecedented flux and time resolution. These attributes of the LCLS revolutionize the experimental investigation of structural dynamics with X-ray techniques by directly following the time evolution of the electron density during the course of a photo-induced biological, chemical, or physical transformation.

The XPP diffraction instrument enables the study of stimulated changes in the structures of molecules and condensed matter systems. The changes are stimulated by a short pulse of optical laser light, and observed using X-ray scattering techniques. Femtosecond-level synchronization between the optical laser and the LCLS X-ray pulse allows sub-picosecond time resolution. 

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