A tandem‐double‐slit optical system was constructed to evaluate the practical beam emittance of undulator radiation. The optical system was a combination of an upstream slit (S₁) and downstream slit (S₂) aligned on the optical axis with an appropriate separation. The intensity distribution after the double slits, I(x₁, x₂), was measured by scanning S₁ and S₂ in the horizontal direction. Coordinates having intensity were extracted from I(x₁, x₂), whose contour provided the standard deviation ellipse in the x₁–x₂ space. I(x₁, x₂) was converted to the corresponding distribution in the phase space, I(x₁, x₁′). The horizontal beam emittance was evaluated to be 3.1 nm rad, which was larger than the value of 2.4 nm rad estimated by using ray‐tracing. It was found that the increase was mainly due to an increase in beam divergence rather than size.

中文翻译：

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串联-双缝光学系统测量波动波辐射的水平光束发射率。

构造了一个串联-双缝光学系统，以评估波动波辐射的实际光束发射率。光学系统是在光轴上以适当间隔对准的上游缝隙（S ₁）和下游缝隙（S ₂）的组合。通过在水平方向上扫描S ₁和S ₂来测量双狭缝之后的强度分布I（x ₁，  x ₂）。从I（x ₁，  x ₂）中提取具有强度的坐标，其轮廓提供了标准偏差椭圆。x ₁ – x ₂空间。I（x ₁，  x ₂）转换为相空间I（x ₁，x ₁ '）中的相应分布。评估的水平光束发射率为3.1 nm rad，它大于使用射线追踪估计的2.4 nm rad的值。发现增加的主要原因是光束发散的增加而不是尺寸的增加。