FEMTOSECOND TIME RESOLUTION IN X-RAY-DIFFRACTION EXPERIMENTS

This paper presents the theoretical background for a synthesis of femt osecond spectroscopy and x-ray diffraction. When a diffraction quality crystal with 0.1-0.3 mm overall dimensions is photoactivated by a fem tosecond laser pulse (physical length = 0.3 mu m), the evolution of mo lecules at separated points in the crystal will not be simultaneous be cause a finite time is required for the laser pulse to propagate throu gh the body of the crystal. Utilizing this lack of global crystal sync hronization, topo-graphic x-ray diffraction may enable femtosecond tem poral resolution to be achieved from reflection profiles in the diffra ction pattern with x-ray exposures of picosecond or longer duration. S uch x-ray pulses are currently available, and could be used to study f emtosecond reaction dynamics at atomic resolution on crystals of both small- and macro-molecules. A general treatment of excitation and diff raction geometries in relation to spatial and temporal resolution is p resented.