X-ray lasers

One of the great barriers to improving our understanding of the molecular basis of life is that we do not yet have any way of examining individual macromolecules in living tissue. The progress made so far in unravelling the structures of biological macromolecules is based on painstaking chemical and x-ray crystallographic analyses of pure, crystalline samples of a given macromolecule.1 This situation could, however, be completely revolutionized if a source of coherent x rays were available. Although, as we shall show below, the realizaton of this goal is beset with difficulties, experiments aimed towards its accomplishments are under way, as shown in figure 1.