Oscillations of the X-ray absorption coefficient beyond an absorption edge. The physical cause of EXAFS is the modification of the final state of a photoelectron wave function caused by back-scattering from atoms surrounding the excited atom due to internal diffraction. EXAFS is used to determine structure in chemical, solid state, or biological systems; it is especially useful in those systems in which it is not possible to use diffraction techniques. EXAFS experiments are usually performed using synchrotron radiation. It is possible to interpret EXAFS experiments using single-scattering theory for short-range order.

Relatedly, there is another type of inner diffraction at lower photon energies than EXAFS. This involves more surrounding atoms than EXAFS. Internal diffraction of this type gives rise to X-ray absorption near-edge structure (XANES). It is necessary to use multiple-scattering calculations to interpret XANES. Like EXAFS, XANES is used in structure determinations. XANES is also called NEXAFS (near-edge X-ray absorption fine structure).