The original X-ray diffraction experiment was based on an idea of von Laue and conducted by Friedrich and Knipping (Friedrich et al 1912). It earned von Laue the Nobel Prize for Physics in 1914. The basis of the idea was that if X-rays were electromagnetic waves then their wavelengths might be of the same order as the interatomic separation in crystals and diffraction would be observed. The original diffraction photograph was from a crystal of copper sulphate.

The essential feature of the Laue method, as it became called, is that the incident X-ray beam is polychromatic and the crystal sample is held stationary. All the X-rays emitted by the emission tube and passing through the tube exit window are allowed to impinge onto the sample; no special filtering or monochromatisation is employed. The Bremsstrahlung continuum and the characteristic emission lines constitutes the incident spectrum of X-rays. This beam hits the stationary crystal and the spots making up the diffraction pattern arise from the different wavelengths. A given reflecting plane in the crystal extracts from the beam the particular wavelength which allows constructive interference or reflection to occur. In contrast to the angular rocking width of a reflection in the monochromatic rotating crystal method, in the Laue method each reflection is stimulated by a small range of wavelengths whose mean wavelength lies somewhere in the broad range of incident wavelengths.