Prof. Dr. André Authier (✝︎)

André Authier was a specialist of the dynamical theory of X-ray diffraction by crystals and X-ray topography. He was the first to make a direct observation of the propagation of X-ray wave fields in a crystal at the Bragg reflection and was one of the early contributors to the theory of the diffraction of X-rays by highly deformed crystals.
With co-worker F. Balibar, he determined the limit above which ray theory is no longer applicable. He analysed and explained the formation of the various parts of the image of the defects in X-ray topography. He applied X-ray topography to the characterization and study of crystal defects, such as growth defects as well in synthetic crystals and in minerals, ferroelectric domains and electrical defects in semiconductors. He was interested in the history of Crystallography.
He was the first President of the European Crystallographic Association (1972-1975) and President of the International Union of Crystallography (1990-1993).