ABSTRACT
In this chapter, we discuss a relatively novel class of X-ray sources, collectively referred to as inverse Compton scattering (ICS) sources. The underlying physical process, namely the inverse of the Compton scattering process, involves the scattering of an electron off a photon beam, resulting in the creation of higher energy photons (see Section I, Chapter 1 of this book). In general, ICS sources (also sometimes simply called Thomson or Compton scattering sources, as we will clarify in the next Section) are, thus, based on the collision between a high brightness electron beam and a high intensity laser pulse, as schematically shown in Figure 16.1. The laser pulse e.m. wave induces the electrons of a colliding beam to oscillate, much in an analogous way to what an undulator or wiggler does. The striking difference, however, appears when one compares the electron energy required to get X-ray photons from the different classes of sources. For instance, an electron energy of about 5 GeV is required to get 1 Å wavelength radiation using a 2 cm period undulator, while only 25 MeV electrons are needed for the same final photon energy, when exploiting the Thomson scattering process with a 1 μm-wavelength colliding pulse.
