Phase correction method in a wide detector plane for MIEZE spectroscopy with pulsed neutron beams

Abstract

In this study, we propose a phase correction method for a type of neutron spin echo spectroscopy, known as modulation of intensity with zero effort using a time-of-flight method (TOF-MIEZE). The phase of the MIEZE signal sensitively varies with the neutron flight path lengths. The geometrical lengths from the sample position to the flat detector plane differ depending on the positions on the detector plane. Integrating the phase-shifted signals may decrease the signal contrast solely through the geometrical path-length deviations. To measure the decrement of contrast accurately, which corresponds to the intermediate scattering function, the position-dependent phase shifts must be corrected. The data correction is performed by shifting the MIEZE signal in time depending on path-length deviations, the MIEZE frequency, and neutron wavelengths. In the calculation of path-length deviations, the sample is assumed to be a point scatterer while a detector inclination is taken into account. We also discuss the relation between the frequency shift of TOF-MIEZE signal and path-length deviation, which is helpful to quantify phase shifts larger than 2π. The presented phase correction method is demonstrated with a 32 × 32 cm² area detector for a 200 kHz TOF-MIEZE signal scattered from an elastic sample.