A Laue diffraction pattern is produced in X-ray crystallography when a stationary crystal is illuminated with a continuous spectrum of X-rays. The first X-ray diffraction pictures were taken in this way by Friedrich, Knipping, and Laue in 1912 (1), but the technique has several disadvantages and was completely superseded by data collection with monochromatic radiation. One problem with Laue diffraction is that a single diffracted beam can be composed of reflections from more than one lattice plane. This multiplet problem can easily be explained by Bragg’s law (see Bragg Angle):
where d is the lattice plane distance, qthe reflection angle, and lthe wavelength. Although
it is also equal to
etc. This multiplet problem is most serious for the low angle reflections.
The availability of synchrotron radiation has given new impetus to the Laue technique. Its broad, smooth spectrum, combined with high intensity, allows extremely short exposure times and the possibility of time-resolved data collection. Moreover, an enormous number of reflections is registered with one exposure. In this way, very rapid reactions can be followed in protein crystals, if a way can be found to synchronize all of the protein molecules that make up the crystal (see Enzymes).
