Ruiz-Lopez Mabel, Mehrjoo Masoud, Keitel Barbara, Plönjes Elke, Alj Domenico, Dovillaire Guillaume, Li Lu, Zeitoun Philippe
Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany.
CNRS, Ecole Polytechique-IPP, ENSTA, Chemin de la Hunière, 91761 Palaiseau, France.
Sensors (Basel). 2020 Nov 10;20(22):6426. doi: 10.3390/s20226426.
Wavefront analysis is a fast and reliable technique for the alignment and characterization of optics in the visible, but also in the extreme ultraviolet (EUV) and X-ray regions. However, the technique poses a number of challenges when used for optical systems with numerical apertures (NA) > 0.1. A high-numerical-aperture Hartmann wavefront sensor was employed at the free electron laser FLASH for the characterization of a Schwarzschild objective. These are widely used in EUV to achieve very small foci, particularly for photolithography. For this purpose, Schwarzschild objectives require highly precise alignment. The phase measurements acquired with the wavefront sensor were analyzed employing two different methods, namely, the classical calculation of centroid positions and Fourier demodulation. Results from both approaches agree in terms of wavefront maps with negligible degree of discrepancy.
波前分析是一种快速且可靠的技术，可用于可见光以及极紫外（EUV）和X射线区域的光学元件的对准和特性表征。然而，当该技术用于数值孔径（NA）> 0.1的光学系统时，会带来一些挑战。在自由电子激光FLASH中使用了高数值孔径的哈特曼波前传感器来表征施瓦兹希尔德物镜。这些物镜在EUV中广泛用于实现非常小的焦斑，特别是用于光刻。为此，施瓦兹希尔德物镜需要高精度对准。使用波前传感器获取的相位测量结果采用两种不同方法进行分析，即质心位置的经典计算和傅里叶解调。两种方法得到的波前图结果在差异程度可忽略不计的情况下是一致的。
