Neutron Interferometry Using a Single Modulated Phase Grating

Abstract

Neutron grating interferometry provides information on phase and small-angle scatter in addition to attenuation. Previously, phase grating moir\'e interferometers (PGMI) with two- or three-phase gratings have been developed. These phase-grating systems use the moir\'e far-field technique to avoid the need for high-aspect absorption gratings used in Talbot-Lau interferometers (TLI) which reduce the neutron flux reaching the detector. We first demonstrate through theory and simulations a novel phase grating interferometer system for cold neutrons that requires a single modulated phase grating (MPG) for phase-contrast imaging, as opposed to the two- or three-phase gratings in previously employed PGMI systems. The MPG theory was compared to the full Sommerfeld-Rayleigh Diffraction integral simulator. Then we compared the MPG system to experiments in the literature that use a two-phase-grating-based PGMI with best-case visibility of around 39%. An MPG with a modulation period of 300 micron, pitch of 2 micron, and grating heights with a phase modulation of (pi,0), illuminated by a monochromatic beam, produces a visibility of 94.2% with comparable source-to-detector distance (SDD) as the two-phase-grating-based PGMI. Phase sensitivity, another important performance metric of the grating interferometer, was compared to values available in the literature, viz. the conventional TLI with phase sensitivity of 4.5 x 10E+3 for an SDD of 3.5 m and a beam wavelength of 0.44 nm. For a range of modulation periods, the MPG system provides comparable or greater theoretical maximum phase sensitivity of 4.1 x 10E+3 to 10.0 x 10E+3 for SDDs of up to 3.5 m. This proposed MPG system can provide high-performance PGMI that obviates the need to align two phase gratings.