Measurement of electron beam divergence using OTR-ODR interferometry

Optical transition radiation (OTR) interferometry has been shown to be a useful diagnostic for measuring the divergence of electron beams over a wide range of beam energies (15 MeV-230 MeV). However, beam scattering in the first foil of the interferometer ultimately limits the useful range of such a device. To overcome this effect we have designed and tested a perforated front foil interferometer to measure divergence of electron beams in the range of 100-1000 micro radians. Unscattered beam electrons passing through the holes in the screen produce optical diffraction radiation (ODR), while those passing through the solid portion produce OTR. For the proper hole size, number and screen thickness, the ODR-OTR interferences are readily observable above an incoherent background produced by the scattered electrons. The fringe visibility provides a measurement of beam divergence. The results of proof of principle measurements are presented. In addition, we introduce a novel design for an interferometer useful for the diagnosis of low energy, low emittance beams.