A quantum-mechanical description of Rotating Field Spin Echo

Abstract

Neutron Spin Echo (NSE) is a technique for quasi-elastic neutron scattering with very high energy resolution. The latter is achieved by comparing the Larmor precession angles of a polarized neutron beam in two well-known magnetic fields before and after scattering in a sample. This “spin encoding” or “Larmor labeling” can be implemented by different technical methods, the most established variants being conventional NSE and Neutron Resonance Spin Echo (NRSE). In this publication we discuss Rotating Field Spin Echo (RFSE), a technique for measurements in the low-resolution domain. The analogy to NRSE is demonstrated by deriving the working principle using the quantum-mechanical method of time-evolution operators, a technique that was developed for NRSE in previous publications. Furthermore, we give an estimation of the inherent upper frequency limit of RFSE based on our theory.