Large Angle MIEZE with Extended Fourier Time

Abstract

Modulation of Intensity Emerging from Zero Effort (MIEZE) is a neutron resonant spin echo technique which allows one to measure time correlation scattering functions in materials by implementing radio-frequency (RF) intensity modulation at the sample and detector. The technique avoids neutron spin manipulation between the sample and the detector, and thus could find applications in cases where the sample depolarizes the neutron beam. However, the finite sample size creates a variance in path length between the locations where scattering and detection happens, which limits the contrast in intensity modulation that one can detect, in particular towards long correlation times or large scattering angles. We propose a modification to the MIEZE setup that will enable one to extend those detection limits to longer times and larger angles. We use Monte Carlo simulations of a neutron scattering beam line to show that, by tilting the RF flippers in the primary spectrometer with respect to the beam direction, one can shape the wave front of the intensity modulation at the sample to compensate for the path variance from the sample and the detector. The simulation results indicate that this change enables one to operate a MIEZE instrument at much increased RF frequencies, thus improving the effective energy resolution of the technique. The simulations show that for an incident beam with maximum divergence of 0.33 • , the maximum Fourier time can be increased by a factor of 3.