Coherence properties of third-generation synchrotron sources and free-electron lasers

Abstract

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