Polarisation in Spin-Echo Experiments: Multi-point and Lock-in Measurements

TL;DR

This paper introduces a continuous spin polarisation measurement method in spin-echo experiments using lock-in detection, demonstrating advantages over traditional discrete readings and enabling real-time experiment modeling.

Contribution

It presents a novel continuous measurement technique for spin polarisation in spin-echo experiments, utilizing lock-in detection and real-time simulations for improved accuracy and tracking.

Findings

The new method successfully measures polarisation in helium spin-echo experiments.

It can track changes in beam properties throughout the experiment.

Real-time simulations accurately model complex experimental setups.

Abstract

Spin-echo instruments are typically used to measure diffusive processes and the dynamics and motion in samples on ps and ns timescales. A key aspect of the spin-echo technique is to determine the polarisation of a particle beam. We present two methods for measuring the spin polarisation in spin-echo experiments. The current method in use is based on taking a number of discrete readings. The implementation of a new method involves continuously rotating the spin and measuring its polarisation after being scattered from the sample. A control system running on a microcontroller is used to perform the spin rotation and to calculate the polarisation of the scattered beam based on a lock-in amplifier. First experimental tests of the method on a helium spin-echo spectrometer, show that it is clearly working and that it has advantages over the discrete approach i.e. it can track changes of the beam properties throughout the experiment. Moreover, we show that real-time numerical simulations can perfectly describe a complex experiment and can be easily used to develop improved experimental methods prior to a first hardware implementation.