A Precision Grazing-incidence Angle Error Measurement of a Hard X-ray Condenser Mirror Using Single-grating Interferometry
A Precision Grazing-incidence Angle Error Measurement of a Hard X-ray Condenser Mirror Using Single-grating Interferometry
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单光栅干涉法精密测量硬X射线聚光镜掠入射角误差
DOI：
10.1080/08940886.2013.832585
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发表时间：
2013
影响因子：
--
通讯作者：
and K. Yamauchi
中科院分区：
文献类型：
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作者：
R. Fukui;J. Kim;S. Matsuyama;H. Yumoto;Y. Inubushi;K. Tono;T. Koyama;T. Kimura;H. Mimura;H. Ohashi;M. Yabashi;T. Ishikawa;and K. Yamauchi
第三代同步辐射设备使我们能够使用极高亮度和低发射度的x射线，这些x射线通过聚焦装置有效地集中在纳米级区域。这一进展大大提高了基于扫描显微镜的x射线分析的吞吐量。另一方面，扫描显微镜的空间分辨率直接取决于焦点光斑的大小。许多衍射[，]，折射[，]和反射[，]聚焦装置目前可用于产生小焦斑。反射光学在足够长的工作距离下实现了最高的吞吐量。此外，在上述聚焦装置中，反射装置在硬x射线区域产生的焦斑尺寸最小。全反射镜可达到30 nm以下的焦斑尺寸，而多层反射镜可达到10 nm以下的焦斑尺寸。镜形误差和掠射角度的不对准会显著降低可实现的焦斑尺寸。在硬x射线区域，聚焦镜表面要求的精度分别低于2nm PV和1nm PV，用于sub- 30nm和sub- 10nm聚焦。在sub-30 nm和sub-10 nm聚焦时，掠射入射角误差分别不超过0.5 × 10 - 6rad和0.1 × 10 - 6rad。当前的制造和镜像测试技术的进步已经实现了高度精确的确定性计算过程，可以满足这些要求。制造技术包括离子束计算[，]和弹性发射加工（EEM），而图形测试是使用光学干涉仪[，]或坡度剖面仪[，，]来实现的。相比之下，对准精度仍然是通过传统的光束剖面方法，如刀口扫描方法来评估的。通过光束轮廓和上光入射角调整的迭代过程来优化对准。这个过程非常耗时，并且经常会由于被扫描物体的形状缺陷和/或振动而导致显著的轮廓误差。因此，掠射对准往往决定了可实现的焦斑大小。掠射入射角的误差产生一种彗差，本质上是一种三次函数波前畸变。因此，通过监测波前形状来调整掠射入射角是可能的。波前形状可以通过几种方法表征，如相位检索或平面图[，]。然而，要获得精度小于λ/4的波前形状，即瑞利准则所规定的极限，需要大量的强度信息。此外，这些方法不适合x射线自由电子激光器（XFEL）聚焦中逐射测量的要求。
Third-generation synchrotron radiation facilities enable us to use X-rays of extremely high brightness and low emittance, which are efficiently concentrated into a nanoscale area by a focusing device. Such progress has significantly enhanced the throughput of X-ray analyses based on scanning microscopy. On the other hand, the spatial resolution of scanning microscopy directly depends on the focal spot size. Many diffractive [, ], refractive [, ], and reflective [, ] focusing devices are currently available for producing small focal spots. Reflective optics realize the highest throughput with a sufficiently long working distance. Furthermore, among the above-listed focusing devices, reflective devices produce the smallest focal spot size in the hard X-ray region. A total reflection mirror may attain sub-30 nm focal spot size , while a multilayer mirror may attain sub-10 nm focal spot size . The achievable focal spot size is significantly degraded by errors in the mirror shape and misalignment of grazing-incidence angle. In the hard X-ray region, the focusing mirror surface requires accuracies below 2 nm PV and 1 nm PV for sub-30 nm and sub-10 nm focusing, respectively. The error in the grazing-incidence angle must not exceed 0.5 × 10−6rad and 0.1 × 10−6rad for sub-30 nm and sub-10 nm focusing, respectively. Current advances in fabrication and mirror testing technologies have realized highly accurate deterministic figuring processes that can meet these requirements. Fabrication techniques include ion beam figuring [, ] and elastic emission machining (EEM) , while figure testing is achieved using optical interferometers [, ] or slope profilers [, , ]. In contrast, alignment accuracy is still evaluated by conventional beam profiling methods such as knife-edge scanning methods. The alignment is optimized by an iterative procedure of beam profiling and glazing-incidence angle adjustment. This procedure is very time-consuming and frequently introduces a significant profiling error from shape imperfections and/or vibration of the object to be scanned. Accordingly, the grazing-incidence alignment often determines the achievable focal spot size. The error in the grazing incidence angle generates a coma aberration, which is essentially a wavefront distortion with a cubic function. Hence, adjusting the grazing-incidence angle by monitoring the wavefront shape is possible. The wavefront shape can be characterized by several methods, such as phase retrieval or ptychography [, ]. However, to obtain a wavefront shape of accuracy smaller than λ/4, the limit imposed by Rayleigh's criterion, large amounts of intensity information are required. In addition, these methods are unsuitable for the shot-by-shot measurements demanded in X-ray free-electron laser (XFEL) focusing.