Pincelli T, Grasselli F, Petrov V N, Torelli P, Rossi G
Dipartimento di Fisica, Università degli studi di Milano, Via Celoria 16, 20133 Milano, Italy.
Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Via Campi 213/a, Modena, Italy.
J Synchrotron Radiat. 2017 Jan 1;24(Pt 1):175-187. doi: 10.1107/S1600577516017513.
In this work the experimental uncertainties concerning electron spin polarization (SP) under various realistic measurement conditions are theoretically derived. The accuracy of the evaluation of the SP of the photoelectron current is analysed as a function of the detector parameters and specifications, as well as of the characteristics of the photoexcitation sources. In particular, the different behaviour of single counter or twin counter detectors when the intensity fluctuations of the source are considered have been addressed, leading to a new definition of the SP detector performance. The widely used parameter called the figure of merit is shown to be inadequate for describing the efficiency of SP polarimeters, especially when they are operated with time-structured excitation sources such as free-electron lasers. Numerical simulations have been performed and yield strong implications in the choice of the detecting instruments in spin-polarization experiments, that are constrained in a limited measurement time. Our results are therefore applied to the characteristics of a wide set of state-of-the-art spectroscopy facilities all over the world, and an efficiency diagram for SP experiments is derived. These results also define new mathematical instruments for handling the correct statistics of SP measurements in the presence of source intensity fluctuations.
在这项工作中，从理论上推导了在各种实际测量条件下与电子自旋极化（SP）相关的实验不确定性。分析了光电子电流SP评估的准确性与探测器参数和规格以及光激发源特性之间的函数关系。特别地，探讨了在考虑源强度波动时单计数器或双计数器探测器的不同行为，从而对SP探测器性能给出了新的定义。结果表明，广泛使用的品质因数这一参数不足以描述SP偏振仪的效率，尤其是当它们与诸如自由电子激光等具有时间结构的激发源一起运行时。已经进行了数值模拟，其对自旋极化实验中检测仪器的选择具有重要影响，这些实验受到有限测量时间的限制。因此，我们的结果被应用于世界各地广泛的一系列先进光谱学设施的特性研究，并得出了SP实验的效率图。这些结果还定义了新的数学工具，用于在存在源强度波动的情况下处理SP测量的正确统计数据。
