Centennial of X-ray diffraction: development of an unpromising experiment with a wrong explanation

Abstract

In February 1912 in Munich, P. P Ewald, one of A. Sommerfeld's Ph.D. students, consulted M. Laue on matters related to crystal optics, his thesis subject. During the conversation, Laue conceived the idea that a crystal might act as a three-dimensional diffraction grating to the X-rays. Despite the idea having met with scepticism among his colleagues, Laue succeeded in getting the help of two of W. C. Roentgen's doctorands: F. Friedrich, Sommerfeld's laboratory assistant, and P. Knipping: to undertake the, by now, legendary experiments that originated a new branch of Physics. The results solved two fundamental questions of the time: namely are the X-rays electromagnetic radiation (light) of very short wavelength? And also, do the crystals have spatial periodic arrangements? The affirmative answer to both questions was immediately followed in 1913 by the instrumentation and re-interpretation of the phenomenon through the pioneering work by W. H. Bragg and his son W. L. Bragg, who paved the way to the portentous development of structural crystallography by X-ray diffraction that took place during the last hundred years.