The application of OTR-ODR interferometry to the measurement of the divergence of low energy electron beams

Optical transition radiation (OTR) interferometry has been shown to be a useful diagnostic to measure the divergence of electron beams with energies in the range of 15-100 MeV. A limitation of this method is due to beam scattering in the first foil of the interferometer. To mitigate this undesirable effect we propose to use a perforated first foil in the interferometer. In this case a substantial fraction of the unscattered beam electrons passing through the holes will produce optical diffraction radiation (ODR). The total radiation produced from the first and second foils will be coherent ODR and OTR from unscattered electrons and incoherent ODR and OTR from heavily scattered electrons in the first foil. Such an ODR-OTR interferometer is being designed to measure the divergence at the University of Maryland's Infrared Free Electron Laser (MIRFEL) experiment. Calculations show that the method is capable of measuring beam divergences of the order of one milliradian for beam energies less than 10 MeV.