The EXAFS family tree: a personal history of the development of extended X-ray absorption fine structure.

This paper reviews the history of X-ray absorption spectroscopy (XAS) beginning with the first observation of an absorption edge, through the development of the modern theory and data inversion by the Fourier transform. I stop with my first trip to a synchrotron X-ray source. The study of XAS began at an exciting time for science. Wave mechanics, X-ray diffraction, X-ray scattering from non-crystalline materials experiments developed in parallel with XAS. However, the difficulty of obtaining data from conventional X-ray tubes limited the field to a potentially interesting minor subject. Only with the advent of synchrotron radiation and arrival of modern theory in the 1970s did XAS become widely applicable to fields ranging from environmental to biological sciences. Early developments in experimental technique and theory are emphasized. Since I worked in both the before-synchrotron and after-synchrotron time frames, I had the opportunity to meet some of the early scientists. A number of historical vignettes and photographs of the scientists involved in the development of EXAFS are presented.