Yan J, Qiao S
Department of Physics, Laboratory of Advanced Materials, and Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433, People's Republic of China.
Rev Sci Instrum. 2010 May;81(5):056101. doi: 10.1063/1.3385661.
Here, a new operational mode of an electromagnetic elliptical undulator, called leaf undulator, is proposed and studied. It can provide linearly polarized radiation at an arbitrary polarization direction depending on the magnitude and polarity of the horizontal and vertical magnetic fields. The polarization direction becomes 45 degrees when the horizontal and vertical magnetic fields are equal in strength. It is also able to switch the operational mode to purely circular or elliptical one. To lower the on-axis power density generated by undulators operating in linear mode, different designs have been presented in the past. Leaf undulator can suppress the on-axis power density by an order of magnitude compared to the so-called Knot and Figure-8 undulators, while maintaining comparable photon flux of the fundamental harmonic. Furthermore, it is possible to reach a lower fundamental energy under linear mode than by any other design using comparable magnetic field strengths.
在此，我们提出并研究了一种电磁椭圆波荡器的新运行模式，称为叶片波荡器。它可以根据水平和垂直磁场的大小和极性，在任意极化方向上提供线偏振辐射。当水平和垂直磁场强度相等时，极化方向变为45度。它还能够将运行模式切换为纯圆偏振或椭圆偏振模式。为了降低线性模式下波荡器产生的轴上功率密度，过去已经提出了不同的设计方案。与所谓的纽结和8字形波荡器相比，叶片波荡器可以将轴上功率密度抑制一个数量级，同时保持基波的可比光子通量。此外，在线性模式下，使用可比磁场强度时，它有可能达到比任何其他设计更低的基波能量。
