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The Laue method

Laue in his very first experiments used white radiation of all possible wavelengths and allowed this radiation to fall on a stationary crystal. The crystal diffracted the X-ray beam and produced a very beautiful pattern of spots which conformed exactly with the internal symmetry of the crystal. Let us analyse the experiment with the aid of the Bragg equation. The crystal was fixed in position relative to the X-ray beam, thus not only was the value for d fixed, but the value of $\theta$ was also fixed (see Fig. 20).

 

Figure 20: Transmission Laue camera.

The only possible variables therefore are the integer n and wavelength $\lambda$, with the result that in the Laue photograph each observed reflection corresponds to the first order of reflection of a certain wavelength, the second order of half the wavelength and a third order of a third of the wavelength, and so on. The Laue photograph which is obtained from a single crystal is simply a stereographic projection of the planes of the crystal.

Copyright © 1981, 1997 International Union of Crystallography