Comparative study of single layer, bilayer, and trilayer mirrors with enhanced x ray reflectance in 0.5 to 8 keV energy region

Effective area is one of the most important parameters of x ray telescopes. It can be increased by enlarging the entrance aperture or maximizing the reflectivity through the proper designing and optimization of the reflecting coating. A method to increase the reflectivity of grazing incidence x ray mirrors in the 0.5 to 8 keV energy region is analyzed. The idea consists in the use of a trilayer reflecting coating instead of single layer one e.g., C Ni Pt mirror instead of Pt one . Deposition of low absorbing medium Z and low Z layers onto the top of strongly absorbing high Z material results in essential increase in the reflectivity while keeping the same width of the reflectivity plateau. In particular, C Ni Pt trilayer mirror demonstrates enhancement of the double reflection coefficient by a factor achieving 1.5 to 3.5 compared to that of Pt coated mirror. The effective area of a telescope is also considerably increased. The experimental results are in a very good agreement with the theoretical predictions. In addition, the C Ni Pt trilayer mirror exhibits a reasonable thermal stability and a relatively low compressive stress of about amp; 8722;550 amp; 8201; amp; 8201;MP