Optical diffraction-dielectric foil radiation interferometry diagnostic for low energy beams

We have developed and used a novel optical diffraction-dielectric foil radiation interferometer to measure the divergence of the low energy (8 - 14 MeV) ANL-AWA electron beam. Our interferometer employs an electro-formed micromesh first foil to overcome the inherent limitation due to scattering in the solid first foil of a conventional OTR interferometer (OTRI) and an optically transparent dielectric foil. The interferences of forward directed optical diffraction radiation (ODR) from the mesh and radiation from the dielectric foil is observed in transmission. This geometry allows a small gap between the foils (1 - 2 mm), which is required to observe fringes from two foils at low beam energies. Our measurements indicate that a single Gaussian distribution is sufficient to describe the angular phase space of the measured beam.