Reflectance Test Method of X-ray Optics on the 100-m X-ray Test Facility

Abstract

Reflectance is a key topic in soft X-ray optics research and serves as the foundation for the study of X-ray astronomical satellites and payload performance. Since its establishment, the 100-m X-ray Test Facility (100XF) has been continuously developing various testing functionalities, including calibration of timing, imaging, and energy response. This paper provides a detailed description of the X-ray optics reflectance test method based on the 100XF, which is applicable to various grazing incident X-ray optics, including Wolter-I and lobster-eye types, significantly expanding the application scope of the 100XF. A flat mirror sample (SiO2 coated on Si wafer) are tested. Results of the variation of reflectivity with angle @ C-Kα (0.28 keV), Al-Kα(1.49 keV) and Ti-Kα(4.50 keV) are presented among the description. Additionally, reflectance test method has been applied to the coating reflectivity study of the enhanced X-ray Timing and Polarimetry Mission (eXTP) mirror. At the same time, a new method utilizing continuum spectrum of bremsstrahlung was carried out for studying the continuous variation of reflectivity with energy, greatly improving efficiency compared to traditional methods, and all the results show a good agreement with the theoretical values. The deviation between the test values and theoretical values in the low-energy range (1.5-8.0 keV) is less than 10%.