Laue crystallography: coming of age

A renewed interest in the Laue diffraction technique has been brought about by the development of new, more intense and brilliant synchrotron sources along with their insertion devices such as wigglers and undulators, and by the prospect of using these sources to study structural dynamics by time-resolved crystallography. Theoretical studies during the past decade have identified unique features of the polychromatic diffraction geometry and greatly improved our understanding of the Laue method. This led to innovative approaches to Laue data processing and its software implementation. Most of the problems in Laue data processing, considered for a long time to limit the applicability of the technique, have been solved. Significant advances have also been made in the development of synchrotron sources, beamline optics and instrumentation, and the X-ray detectors. Static Laue experiments yield structure amplitudes that equal those from monochromatic data in quality. When coupled with careful consideration of data-collection strategies and reaction initiation in crystals, a series of successful time-resolved Laue experiments on biological systems have been conducted. These have revealed information on structural dynamics inaccessible to any other conventional diffraction method. These static and time-resolved experiments demonstrate that the Laue method is coming of age. They also suggest avenues for future improvements: a correct treatment of finite mosaic spread and the associated energy width of Laue spots; consideration of diffuse scattering; and determination of intermediate structures in time-resolved experiments in which those intermediates do not attain a high concentration.