Analysis of Multi-Frequency Oscillating Magnetic Fields by Neutron Spin Interferometry

We have developed a methodology for analyzing multi-frequency oscillating magnetic fields using neutron spin interferometry. A theoretical formulation was derived of the contrast and the phase of the interference pattern for an input oscillating magnetic field consisting of a series of sine functions with multiple frequencies. According to the formulation, the contrast decays due to the dispersion of the Larmor precession induced by an oscillating field. The formulation also predicts that the phase of the interference pattern does not constant in contrast to single-frequency cases. We conducted an experiment in JRR-3 C3-1-2-2 beam port to confirm the formulation in the cases of two-frequency oscillating fields in the frequency range from 2500 Hz to 10000 Hz. The measured interference patterns showed reasonable agreement with the theoretical predictions.