Coherent Cerenkov radiation and laser oscillation in a photonic crystal
  We demonstrate that photonic crystals can be used to generate powerful and highly coherent laser radiation when injecting a beam of free electrons. Using theoretical investigations we present the startup dynamics and coherence properties of such laser, in which gain is provided by matching the optical phase velocity in the photonic crystal to the velocity of the electron beam. 
T. Denis, M.V. van Dijk, J.H.H. Lee, R. van der Meer, A. Strooisma,   P.J.M. van der Slot, W.L. Vos, K.J. Boller
physics.optics