When the trajectory of an incident beam is oriented parallel to the grooves of a periodic grating structure the radiation beam is diffracted off‐plane orthogonal to the plane of incidence. The diffraction efficiency in this condition is very high and in a grating with a sawtooth profile it can approach the reflection coefficient for a simple mirror, when the diffraction order of interest follows the direction for specular reflection at the flat part of the steps. When this concept is used in a plane grating in a monochromator for synchrotron radiation sources, the incident beam is almost always collimated in order to minimize any deterioration of the beam properties due to aberrations, which will be introduced in the diffraction process when an uncollimated beam is used. These aberrations are very severe when the groove density is constant. It will be shown that the effect of these aberrations can be corrected after the diffraction by the use of astigmatic focusing. The latter can be provided by a crossed mirror pair with different focal lengths in the corresponding orthogonal directions. Then a monochromator based on this concept can provide source size limited spectral resolution in an uncollimated incident beam. This is identical to the spectral resolution that can be provided by the same grating when operated at the same position in a collimated incident beam. The source size limited spectral resolution in this case corresponds to a high spectral resolving power of better than ΔE/E = 10 000 for photon energies around 300 eV in the soft X‐ray range.

中文翻译：

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在发散的入射光束中进行离面衍射的极端紫外/软X射线单色仪中获得高光谱分辨率时

当入射光束的轨迹平行于周期性光栅结构的凹槽定向时，辐射束会在与入射平面正交的平面外衍射。在这种情况下，衍射效率非常高，在具有锯齿形轮廓的光栅中，当感兴趣的衍射级次在台阶的平坦部分处遵循镜面反射的方向时，它可以达到简单反射镜的反射系数。当此概念用于单色仪中用于同步加速器辐射源的平面光栅中时，入射光束几乎总是被准直，以最小化由于像差引起的光束特性的任何劣化，当非准直光束出现在衍射过程中时，会在衍射过程中引入这种光束。用来。当凹槽密度恒定时，这些像差非常严重。将显示出，在衍射之后，可以通过使用像散聚焦来校正这些像差的影响。后者可以由在相应的正交方向上具有不同焦距的交叉镜对提供。然后，基于此概念的单色仪可以在未准直的入射光束中提供光源尺寸受限的光谱分辨率。这与在准直的入射光束中的相同位置上操作时，同一光栅可以提供的光谱分辨率相同。在这种情况下，受源尺寸限制的光谱分辨率对应于优于Δ的高光谱分辨能力 后者可以由在相应的正交方向上具有不同焦距的交叉镜对提供。然后，基于此概念的单色仪可以在未准直的入射光束中提供光源尺寸受限的光谱分辨率。这与在准直的入射光束中的相同位置上操作时，同一光栅可以提供的光谱分辨率相同。在这种情况下，受源尺寸限制的光谱分辨率对应于优于Δ的高光谱分辨能力 后者可以由在相应的正交方向上具有不同焦距的交叉镜对提供。然后，基于此概念的单色仪可以在未准直的入射光束中提供光源尺寸受限的光谱分辨率。这与在准直的入射光束中的相同位置上操作时，同一光栅可以提供的光谱分辨率相同。在这种情况下，受源尺寸限制的光谱分辨率对应于优于Δ的高光谱分辨能力对于在软X射线范围内大约300 eV的光子能量，E / E = 10000。