Hand Matthew, Wang Hongchang, Maccherozzi Francesco, Apollonio Marco, Zhu Jingtao, Dhesi Sarnjeet S, Sawhney Kawal
Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
Institute of Precision Optical Engineering, Tongji University, Shanghai 200092, People's Republic of China.
J Synchrotron Radiat. 2018 Mar 1;25(Pt 2):378-384. doi: 10.1107/S1600577518001960. Epub 2018 Feb 22.
Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length λ = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes-Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 µm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes-Poincaré parameters for all linear angles would require alteration of both these aspects.
插入式设备因其能够提供高亮度X射线束而在世界各地的同步辐射设施中得到应用。APPLE-II型波荡器因其能够在多种光子束偏振态之间切换的能力而尤为重要。一台高精度软X射线偏振计已被用于研究安装在钻石光源I06光束线上的一台APPLE-II型波荡器（周期长度λ = 64 mm）的偏振校准。在一系列线性任意角度下对光束偏振态的系统测量结果已与根据理论计算的给定波荡器间隙和行相位参数集的预期结果进行了比较。从测量数据中确定相应的斯托克斯 - 庞加莱参数揭示了两者之间的差异。波荡器校准表中包含的能量/偏振组合数量有限，这使得对于缺失点需要使用插值，预计这会导致差异。然而，通过将电子束通过波荡器的轨道至少改变160 µm，发现对于某些线性偏振，差异可以得到校正。总体而言，建议对所有线性角度的斯托克斯 - 庞加莱参数进行完全校正需要改变这两个方面。
