Mo/Si multilayers used for the EUV normal incidence solar telescope

This paper first reviews an EUV normal incidence solar telescope that we have developed in our lab. The telescope is composed of four EUV telescopes and the operation wavelengths are 13.0 nm, 17.1 nm, 19.5 nm, and 30.4 nm. These four wavelengths, fundamental to the research of the solar activity and the atmosphere dynamics, are always chosen by the EUV normal incidence solar telescope. In the EUV region, almost all materials have strong absorption, so optics used in this region must be coated by the multilayer. The Mo/Si multilayers used for the EUV normal incidence solar telescope are designed and fabricated by the magnetron sputtering coating machine. The characteristics of these multilayers, such as reflectivity and thermal stability at wavelengths of 13.0 nm, 17.1 nm, 19.5 nm and 30.4 nm, are also described. All the multilayers were measured by a hard X-ray diffractometer (XRD) and an EUV/soft X-ray reflectometer (EXRR) before and after heating (in a vacuum chamber) at 100°C for 24 hours and at 200°C for 1 hour and 4 hours. The results show that Mo/Si multilayers have high reflectivity at 13.0 nm, 17.1 nm, and 19.5 nm but low at 30.4 nm. We found no change in the reflectivity and center wavelength of these multilayers by comparing the reflectivity curves before and after heating. This suggests the thermal stability of Mo/Si multilayers may meet our requirement in future solar observation missions.