  Neutron grating interferometry is an advanced method in neutron imaging that
allows the simultaneous recording of the transmission, the differential phase
and the dark-field image. Especially the latter has recently received high
interest because of its unique contrast mechanism which marks ultra-small-angle
neutron scattering within the sample. Hence, in neutron grating interferometry,
an imaging contrast is generated by scattering of neutrons off micrometer-sized
inhomogeneities. Although the scatterer cannot be resolved it leads to a
measurable local decoherence of the beam. Here, a report is given on the design
considerations, principles and applications of a new neutron grating
interferometer which has recently been implemented at the ANTARES beamline at
the Heinz Maier-Leibnitz Zentrum. Its highly flexible design allows to perform
experiments such as directional and quantitative dark-field imaging which
provide spatially resolved information on the anisotropy and shape of the
microstructure of the sample. A comprehensive overview of the nGI principle is
given, followed by theoretical considerations to optimize the setup performance
for different applications. Furthermore, an extensive characterization of the
setup is presented and its abilities are demonstrated on selected case studies:
(i) dark-field imaging for material differentiation, (ii) directional
dark-field imaging to mark and quantify micrometer anisotropies within the
sample and (iii) quantitative dark-field imaging, providing additional size
information on the sample's microstructure by probing its autocorrelation
function.
