Abstract
Image-forming focusing mirrors were employed to demonstrate their applicability to two different modalities of neutron imaging, phase imaging with a far-field interferometer, and magnetic-field imaging through the manipulation of the neutron beam polarization. For the magnetic imaging, the rotation of the neutron polarization in the magnetic field was measured by placing a solenoid at the focus of the mirrors. The beam was polarized upstream of the solenoid, while the spin analyzer was situated between the solenoid and the mirrors. Such a polarized neutron microscope provides a path toward considerably improved spatial resolution in neutron imaging of magnetic materials. For the phase imaging, we show that the focusing mirrors preserve the beam coherence and the path-length differences that give rise to the far-field moiré pattern. We demonstrated that the visibility of the moiré pattern is modified by small angle scattering from a highly porous foam. This experiment demonstrates the feasibility of using Wolter optics to significantly improve the spatial resolution of the far-field interferometer.
Highlights
Most existing neutron-imaging instruments can be described as pinhole cameras that measure the neutron shadow of a sample
We demonstrate how to exploit the advantages offered by Wolter optics to polarized imaging, which we refer to as Wolter optics, Helium-3 Neutron imaging of Magnetic Samples (WHIMS), and Wolter Optics Far-Field Interferometry (WOOFF)
We have demonstrated that Wolter optics can be used to obtain high spatial resolution images of the magnetic field distribution
Summary
Most existing neutron-imaging instruments can be described as pinhole cameras that measure the neutron shadow of a sample. In such cameras, the geometric blur, which fundamentally limits spatial resolution, is given by λg = z D/(L − z), where z is the sample to detector distance, D is the beam defining aperture, and L is the aperture to detector distance. Due to the inherent low intensity of neutron sources, D is of order 1 cm. This size limitation precludes the use of geometric magnification to improve spatial resolution, and currently achievable spatial resolutions reach ~10 μm. Neutron refractive lenses have very long focal lengths (~100 s of meters) and are strongly chromatic [1]
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