Coherence Properties of Third-Generation Synchrotron Sources and Free-Electron Lasers

Coherence and interference phenomena are the fundamental properties of light. Synchrotrons andx-ray free-electron lasers (XFEL) are nowadays the principal sources of high-brilliance hard x-rayradiation. In this chapter we present an overview of theoretical developments and experimentalresults on measurements of coherence properties of synchrotron radiation and XFEL sources. Westart with an overview of the basic principles of the theory of optical coherence and apply thisgeneral theory to the description of coherence properties of third-generation synchrotron sourcesas well as XFELs. We then describe propagation of partially coherent x-ray radiation throughthe beamline optics, especially focusing optics. We next proceed with the experimental methodsof coherence measurements based on amplitude correlation measurements (e.g. Young’s doublepinholeexperiments). Then we focus on the intensity correlation measurements (Hanbury Brownand Twiss experiments) demonstrating their advantages and complications. Finally, we give a shortoverview of the coherence properties of the new-generation x-ray sources that are in the planningstage. With the construction of the next-generation x-ray facilities aiming to reach the diffractionlimit, the necessity to study and understand the coherence properties of the x-ray sources willbecome even more important. This knowledge will pave the way for new applications of coherentx-rays to study structure and dynamics of matter at various conditions