Spontaneous and Induced Radiation by Relativistic Particles in Natural   and Photonic Crystals. Crystal X-ray Lasers and Volume Free Electron Lasers   (VFEL)
  The mechanisms of spontaneous and induced radiation produced by relativistic particles passing through natural and photonic crystals are reviewed. The theory of Volume Free Electron Lasers based on spontaneous radiation in natural and photonic crystals is presented. 
V.G. Baryshevsky
physics.acc-ph physics.optics