Twisted Radiation by Electrons in Spiral Motion
  We theoretically show that a single free electron in circular/spiral motion radiates an electromagnetic wave possessing helical phase structure and carrying orbital angular momentum. We experimentally demonstrate it by double-slit diffraction on radiation from relativistic electrons in spiral motion. We show that twisted photons should be created naturally by cyclotron/synchrotron radiations or Compton scatterings in various situations in cosmic space. We propose promising laboratory vortex photon sources in various wavelengths ranging from radio wave to gamma-rays. 
M. Katoh, M. Fujimoto, N. S. Mirian, T. Konomi, Y. Taira, T. Kaneyasu,   M. Hosaka, N. Yamamoto, A. Mochihashi, Y. Takashima...
physics.optics physics.acc-ph