Aberration-free diffraction-grating neutron interferometer

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 compensatable by adding a third diffraction grating, which also permits the interferometer to operate with an uncollimated and unmonochromatized illuminating beam thereby raising its efficiency. A fourth diffraction grating additionally permits compensation of effects of the terrestrial rotation that affect the performance of a large interferometer in which the spatial separation of beams can be as great as a few meters. It is demonstrated to be practically possible to implement an interferometer for neutrons having a wavelength λ = 20 A 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. (orig.)