Modulation of intensity emerging from zero effort (MIEZE) with extended Fourier time at large scattering angle

Abstract

Modulation of Intensity Emerging from Zero Effort (MIEZE) is a neutron resonant spin echo technique that allows one to measure time correlation scattering functions in materials by implementing radio-frequency (RF) intensity modulation at the sample and the 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 the path length between the locations where scattering and detection happen, which limits the contrast in intensity modulation that one can detect, in particular, toward 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 beamline 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. For the MIEZE instrument simulated, it shows that for an incident beam with the maximum divergence of 0.33°, the maximum Fourier time can be increased by a factor of 3.

MIASANS at the longitudinal neutron resonant spin-echo spectrometer RESEDA

“…Modulation of Intensity with Zero Effort (MIEZE) is a neutron resonant spin-echo technique variation where potential information loss via depolarization of the Larmor precessing spins prepared by the resonant flippers is preempted by placing a spin analyzer just before the sample position, which results in an intensity modulated neutron beam downstream of the analyzer [27][28][29][30][31][32][33]. No further beam manipulation components are placed between the sample and the detector in contrast to conventional NSE and NRSE.…”

“…However, the signal in MIEZE studies degrades for large scattering angles due to path length differences, for which there are currently no feasible compensation methods for the longitudinal configuration of RESEDA. (However, note that in the transverse MIEZE configuration there are multiple viable ways to do such compensation [33,43]) The strength of this signal reduction has been experimentally quantified for different momentum transfers [18] and agrees well with the calculated expectations [44]. Fortunately though, all commissioning and scientific studies clearly show that the low angle regime is favorable for the MIEZE technique, as flight path differences of neutron trajectories from the sample to the detector [45] play only a minor role [46,47] and the full resolution can be exploited without restrictions on the sample geometry.…”