Geckeler Ralf D, Just Andreas, Krause Michael, Schnabel Olaf, Lacey Ian, English Damon, Yashchuk Valeriy V
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
Schnabel Elektronische Messtechnik, Rosengarten 10, 22880 Wedel, Germany.
J Synchrotron Radiat. 2024 Jul 1;31(Pt 4):670-680. doi: 10.1107/S1600577524003552. Epub 2024 Jun 5.
Deflectometric profilometers are used to precisely measure the form of beam shaping optics of synchrotrons and X-ray free-electron lasers. They often utilize autocollimators which measure slope by evaluating the displacement of a reticle image on a detector. Based on our privileged access to the raw image data of an autocollimator, novel strategies to reduce the systematic measurement errors by using a set of overlapping images of the reticle obtained at different positions on the detector are discussed. It is demonstrated that imaging properties such as, for example, geometrical distortions and vignetting, can be extracted from this redundant set of images without recourse to external calibration facilities. This approach is based on the fact that the properties of the reticle itself do not change - all changes in the reticle image are due to the imaging process. Firstly, by combining interpolation and correlation, it is possible to determine the shift of a reticle image relative to a reference image with minimal error propagation. Secondly, the intensity of the reticle image is analysed as a function of its position on the CCD and a vignetting correction is calculated. Thirdly, the size of the reticle image is analysed as a function of its position and an imaging distortion correction is derived. It is demonstrated that, for different measurement ranges and aperture diameters of the autocollimator, reductions in the systematic errors of up to a factor of four to five can be achieved without recourse to external measurements.
偏折轮廓仪用于精确测量同步加速器和X射线自由电子激光的光束整形光学元件的形状。它们通常使用自准直仪，通过评估探测器上标线片图像的位移来测量斜率。基于我们对自准直仪原始图像数据的特殊访问权限，讨论了通过使用在探测器不同位置获得的一组标线片重叠图像来减少系统测量误差的新策略。结果表明，诸如几何畸变和渐晕等成像特性可以从这组冗余图像中提取出来，而无需借助外部校准设备。这种方法基于标线片本身的特性不会改变这一事实——标线片图像的所有变化都是由于成像过程引起的。首先，通过结合插值和相关性，可以以最小的误差传播确定标线片图像相对于参考图像的偏移。其次，对标线片图像的强度作为其在电荷耦合器件（CCD）上位置的函数进行分析，并计算渐晕校正。第三，对标线片图像的大小作为其位置的函数进行分析，并得出成像畸变校正。结果表明，对于自准直仪的不同测量范围和孔径直径，无需进行外部测量即可将系统误差降低多达四到五倍。
