LaueDiffraction

Laue diffraction, also known as the Laue method, is an early X-ray diffraction technique used to study crystalline materials by irradiating a crystal with a polychromatic (white) X-ray beam. It was developed by Max von Laue and demonstrated in 1912 as a means to probe crystal structure and orientation without requiring a monochromatic source.

Principle and pattern formation: In Laue diffraction, constructive interference occurs when the difference between the incident and diffracted wavevectors matches a reciprocal lattice vector of the crystal. Because the incident beam contains many wavelengths, different lattice planes can diffract at different wavelengths, producing a set of discrete diffraction spots. The geometry and distribution of these spots reflect the crystal’s orientation, symmetry, and, to a limited extent, lattice parameters. The concept is often visualized with the Ewald construction, which helps explain which spots appear for a given crystal orientation and spectrum.

Experimental approach: A crystal is mounted on a goniometer and exposed to a stationary polychromatic X-ray beam. Diffraction spots are recorded on photographic film or a modern detector. By rotating the crystal and capturing multiple patterns, or by repositioning the detector, one can index the spots to specific lattice planes and determine the crystal’s orientation. The method is particularly valued for rapid qualitative assessment and for providing initial orientation without requiring a monochromatic source.

Applications and role: Laue diffraction is used to determine crystal orientation, diagnose crystal quality, and aid in structure determination, especially for single crystals where quick, non-destructive orientation information is advantageous. While largely supplanted in precision work by monochromatic Bragg methods, Laue techniques remain a foundational tool in crystallography and materials science.