Tamtögl Anton, Davey Benjamin, Ward David J, Jardine Andrew P, Ellis John, Allison William
Cavendish Laboratory, J. J. Thompson Avenue, Cambridge CB3 0HE, United Kingdom.
Rev Sci Instrum. 2018 Feb;89(2):023902. doi: 10.1063/1.5017276.
Spin-echo instruments are typically used to measure diffusive processes and the dynamics and motion in samples on ps and ns time scales. 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.
自旋回波仪器通常用于测量扩散过程以及样品在皮秒和纳秒时间尺度上的动力学和运动。自旋回波技术的一个关键方面是确定粒子束的极化。我们提出了两种在自旋回波实验中测量自旋极化的方法。目前使用的方法基于进行多次离散读数。新方法的实施涉及连续旋转自旋并在其从样品散射后测量其极化。运行在微控制器上的控制系统用于执行自旋旋转，并基于锁相放大器计算散射束的极化。在氦自旋回波光谱仪上对该方法进行的首次实验测试表明，它显然是有效的，并且相对于离散方法具有优势，即它可以在整个实验过程中跟踪束特性的变化。此外，我们表明实时数值模拟可以完美地描述复杂的实验，并且可以很容易地用于在首次硬件实现之前开发改进的实验方法。
