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

Yang Yang,Andrey A Sokolov,Qiushi Huang,Yingyu Liao,Zhuangzhuang Zhang,Igor V Kozhevnikov,Zhong Zhang,Runze Qi,Zhanshan Wang

doi:10.1117/1.jatis.6.4.044001

Abstract

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 −550 MPa.

Highlights

Advancements in x-ray space astronomy are essentially based on progressive increases in the performance of x-ray telescopes’ effective area, angular resolution, and field of view.[1,2,3]
The calculations were carried out using bulk density of the mirror materials, the optical constants being taken from the Centre for X-Ray Optics (CXRO) database.[12]
The layers were deposited onto glass substrates (Schott D263 glass, 40 mm × 20 mm in size) by a direct current (DC) magnetron sputtering technique using a dedicated sputtering system designed at the Institute of Precision Optical Engineering of Tongji University.[23,24]

Summary

Introduction

Advancements in x-ray space astronomy are essentially based on progressive increases in the performance of x-ray telescopes’ effective area, angular resolution, and field of view.[1,2,3] The effective area characterizes the ability of a telescope to collect incident radiation. It is determined by the geometrical size of the open entrance aperture and the reflectance of the telescope mirrors. The XMM-Newton telescope[5] has a larger effective area of 1400 cm[2] at 1 keV and a moderate angular resolution of 15 arc sec. The Athena telescope,[7] which is under development for launch in ∼2030, will have an unprecedented effective area of 14;000 cm[2] at 1 keV

Methods

Results

Conclusion