This article's lead section may be too long for the length of the article. Please help by moving some material from it into the body of the article. Please read the layout guide and lead section guidelines to ensure the section will still be inclusive of all essential details. Please discuss this issue on the article's talk page.(August 2017)
X-ray Photon Correlation Spectroscopy (XPCS) is a novel technique that exploits a coherentX-raysynchrotron beam to measure the dynamics of a sample. By recording how coherent speckle fluctuations in time, one can measure a time correlation function, and thus measure the timescale processes of interest (diffusion, relaxation, reorganization, etc.). XPCS is used to study the slow dynamics of various equilibrium and non-equilibrium processes occurring in condensed matter systems.
XPCS experiments have the advantage of providing us with the information of dynamical properties of materials (e.g. vitreous materials), while other experimental techniques can only provide information about the static structure of the material. This technique is based on the generation of a speckle pattern by the scattered coherent light originating from a material where some spatial inhomogeneities are present. A speckle pattern is a diffraction limited structure factor, and is typically observed when laser light is reflected from a rough surface, or from dust particles performing Brownian motion in air. The observation of speckle patterns with hard X-rays has just been demonstrated in the last few years. This observation is only possible now because of the development of new synchrotron radiation X-ray sources that can provide sufficient coherent flux.