Diffraction-grating neutron interferometers

Aberration distortions of wavefronts in a very cold neutron interferometer using diffraction gratings are analyzed. Aberrations that considerably reduce the efficiency of a two-grating interferometer are shown to be fully compensable by adding a third diffraction grating, which also permits the interferometer to operate with a non-collimated and non-monochromatized illuminating beam thereby raising its efficiency. A fourth diffraction grating additionally permits compensation of effects of the terrestrial rotation that affect performance of a large interferometer in which the spatial separation of beams can be of the order of a few meters. It is demonstrated to be practically possible to implement an interferometer for neutrons having a wavelength λ = 20 Å and to use it in experiments aimed at finding the electric charge of the neutron at the level of 10 ^-23 to 10 ^-22 of the electronic charge.