MAX VON LAUE (1879 - 1960). Interferenzerscheinungen bei Röntgenstrahlen. (Sitzungsberichte der Königlich Bayerischen Akademie der Wissenschaften, Mathematische-Physische Klasse 1912, 42, 303-322.)

Laue received his doctorate in theoretical physics under Max Planck (1856 - 1947) in 1903 from the University of Berlin, and his early research focused on optics and Einstein's theory of special relativity. Laue became a Privatdozent at the University of Munich in 1909, an associate professor at Zurich in 1912, and a full professor at Frankfurt in 1914. In 1921, he was elected to membership in the Prussian Academy of Sciences. In the 1930s, he was one of the few who protested the dismissal of Albert Einstein and other Jewish physicists following the Nazi seizure of power. Active up to the end, Laue died in his eighty-first year following an automobile accident.

After Wilhelm Roentgen's (1845 - 1923) discovery of X-rays in 1895, scientists speculated that the rays were actually composed of very short electromagnetic waves, but this hypothesis resisted proof, as it was impossible to construct a diffraction grating with intervals small enough to measure the wavelength. In 1912, Laue came up with the idea of sending X-rays through crystals, arguing that the supposed regular structure of their atoms would approximate the intervals of a diffraction grating.

Laue's associate Walter Friedrich (1883 - 1968), together with student Paul Knipping (1883 - 1935), began experimenting on 12 April 1912, and found that the irradiation of a copper sulfate crystal with X-rays produced a regular pattern of dark points on a photographic plate placed behind the crystal. The dark points were the result of diffraction, which simultaneously proved two ideas that had hitherto been speculative: first, that X-rays are electromagnetic waves rather than particles and, second, that crystals consisted of periodic arrangements of atoms.

In addition to the observation of diffraction, Laue's paper contains his mathematical explanation of diffraction by a crystal, which is embodied in a set of three related equations now known as the Laue equations.

Laue's discovery was of dual importance: it made it possible to measure the wavelengths of X-rays, and it provided the means for the Braggs' structural analysis of crystals, for which they received the Nobel Prize in 1915.

Complete Dictionary of Scientific Biography. Detroit: Charles Scribner's Sons, 2008, v8, p50-53.

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