Optimized signal deduction procedure for the MIEZE spectroscopy technique

Abstract

A method is reported to determine the phase and amplitude of sinusoidally modulated event rates, binned into four bins per oscillation, based on data generated at the resonant neutron spin-echo spectrometer RESEDA at FRM-II. The presented algorithm relies on a reconstruction of the unknown parameters. It omits a calculation-intensive fitting procedure and avoids contrast reduction due to averaging effects. It allows the current data acquisition bottleneck at RESEDA to be relaxed by a factor of four and thus increases the potential time resolution of the detector by the same factor. The approach is explained in detail and compared with the established fitting procedures of time series having four and 16 time bins per oscillation. In addition the empirical estimates of the errors of the three methods are presented and compared with each other. The reconstruction is shown to be unbiased, asymptotic and efficient for estimating the phase. Reconstructing the contrast increases the error bars by roughly 10% as compared with fitting 16 time-binned oscillations. Finally, the paper gives heuristic, analytical equations to estimate the error for phase and contrast as a function of their initial values and counting statistics.

MIASANS at the longitudinal neutron resonant spin-echo spectrometer RESEDA

“…We have designed a MIEZE set-up as part of the spectrometer RESEDA at FRM II that is optimized for the requirements of small angle neutron scattering (MIASANS). This project builds upon major progress with the longitudinal neutron resonance spin-echo method, achieved in recent years at RESEDA [18,28,29,42,54,56,59]. We have so far demonstrated resonant spin flips up to 3.6 MHz, and established that our CASCADE detector is sufficiently sensitive to the highest frequency intensity modulations currently available.…”

“…In order to extract meaningful results from measurements, the phase difference contained within one detector pixel should be less than 20 • [45, 50]. For the case of a MIEZE frequency f M IEZE = 4.9 MHz (and time resolution of 20 MHz using the 4 point method [59]), then on the outermost edge of the detector where the phase rings are densest there will be a phase difference of 115 • within one pixel. Such an extreme phase difference in one pixel would result in severe reduction in the measured signal (contrast).…”

“…The 1.56 mm pixel size of the CASCADE detector is (much) smaller than the average pixel size of a typical SANS detector (8 mm), and therefore any effects due to the pixelated nature of the detector have not yet been observed in experiments. For example, given a MIEZE frequency of 2.5 MHz (time resolution of 10 MHz using the 4 point method [59]), and using 6 Å neutrons with L SD = 3340 mm, one estimates a phase variation in a single pixel of ∼15 • . This value is still below the threshold of 20 • given in [45,50].…”

Extending MIEZE spectroscopy towards thermal wavelengths

“…λ = 2 Å neutrons this will be reduced to 34 %. The introduction of the new superconducting static field coils requires a better detector than the CASCADE type currently used at RESEDA [38,29,30]. Therefore, we have started exploring different detector technologies for the application in MIEZE.…”