Optimization of the design for beamline with fast polarization switching elliptically polarized undulators

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• 作者：Jiefeng Cao ; Yong Wang ; Ying Zou ; Xiangzhi Zhang ; Yanqing Wu and Renzhong Tai
• 关键词：soft X-ray magnetic circular dichroism beamline ; fast polarization switching ; tandem twin elliptically polarized undulators ; energy resolution
• 刊名：Journal of Synchrotron Radiation
• 出版年：2016
• 出版时间：March 2016
• 年：2016
• 卷：23
• 期：2
• 页码：436-442
• 全文大小：1505K
• ISSN：1600-5775

文摘

Fast switching of X-ray polarization with a lock-in amplifier is a good method for acquiring weak signals from background noise for X-ray magnetic circular dichroism (XMCD) experiments. The usual way to obtain a beam with fast polarization switching is to use two series of elliptically polarized undulators (tandem twin EPUs). The two EPUs generate two individual beams. Each beam has a different polarization and is fast switched into the beamline. It is very important to ensure that the energy resolution, the flux and the spot size at the sample of the two beams are equal in XMCD experiments. However, it is difficult in beamline design because the distances from the two EPUs to the beamline optics are different and the beamline is not switchable. In this work, a beamline design without an entrance slit for fast polarization switching EPUs is discussed. The energy resolution of the two beams can be tuned to be equal by minor rotation of the optics in the monochromator. The flux of the two beams can be balanced through separation blades X, Y in the exit slit, and by adjusting the position of the X blades along the beam. The spot size of the two beams can be adjusted to be equal by shifting the sample as well.