Contact Information
Department of Physics525 Northwestern Avenue
West Lafayette, IN
47907-2036
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Telephone:
(765) 494-2970
Fax:
(765) 494-0706
Past Colloquia: Prof. Andre' Authier
Special Physics Colloquium
April 5, 2004
Prof. Andre' Authier
Laboratoire de Mineralogie et Cristallographie
Universite' Pierre et Marie Curie
Paris (France)
Title: The Major Steps in the Development of the Dynamical Theory of
X-ray Diffraction: from the Early Days to Modern Times
The dynamical diffraction theory is used to describe the diffraction
by perfect or nearly perfect crystals, such as those used in high-
technology materials (semiconductors, piezoelectric, ferroelectric,
magnetic crystals, crystals for non-linear optics etc.) or in
optical elements for synchrotron radiation, in contrast to the
approximate kinematical theory used for structure determinations
or powder analysis. Its bases were laid by Ewald in his thesis
before the discovery of x-ray diffraction in 1912 and actually
led to it. At first the dynamical theory of Ewald, Darwin and
von Laue dealt only with plane waves and perfect crystals. It was
checked with two-beam rocking curves for a very few nearly perfect
samples of minerals such as calcite, quartz, diamond or rock salt.
Then came the proofs of the physical existence of the wavefields,
a concept introduced by Ewald in 1913, rediscovered by Bloch in 1928
and known in solid state physics as "Bloch Waves".
The rapid development of the dynamical theory and its applications
in the late fifties and early sixties is to be associated with the
availability of higly perfect crystals of silicon and germanium.
It has not relented since and has been encouraged by the advent of
synchrotron radiation.