Crystalline undulator: Current status and perspectives

Abstract

Recent advances in the theory of novel sources of hard electromagnetic radiation,-a crystalline undulator (CU) and a Crystalline Undulator based Laser (CUL), are reviewed. The operating principle of CU is based on the channeling phenomenon. Channeling takes place if a particle enters a crystal at small angle to major crystallographic planes (or axes). The particle becomes confined by the planar or axial potential and move preferably along the plane or axis following its shape. If the planes or axes are periodically bent, the particles move along nearly sinusoidal trajectories. Similarly to what happens in an ordinary undulator, relativistic charged particles radiate electromagneticwaves in the forward direction. The advantage ofCU is that due to extremely strong electrostatic fields inside the crystal the particles are steered much more effectively than by the field of the most advanced superconductive magnets. This allows one to make the period of CU two or even three orders of magnitude smaller then that of the conventional undulator. As a result the frequency of the radiation can reach the hard X-ray and gamma ray range. Similarly as it takes place in an ordinary free electron laser (FEL), the radiation becomes more powerful and coherent if the density of the particle beam is modulated along the beam direction with the period equal to the wavelength of the produced radiation.