Figure 1.

Schematic illustration of a CBT experimental arrangement. X-ray photons incident upon the crystal laminar at x are Bragg scattered and recorded at x′_hkl. During a picosecond x-ray exposure a femtosecond laser pulse sweeps across the crystal laminar, exciting separated lattice points in turn. Because the crystal excitation is not instantaneous, the recorded images contain intensity gradients, Eq. 5, from which electron density maps for structural intermediates can be determined with near-femtosecond temporal resolution.