Optical design of X-ray focusing telescope

Abstract

X-ray focusing telescope is one of the most important equipment for X-ray space observation, which is designed based on the grazing incidence principle. The purpose of x-ray observation is to detect the black holes of various sizes in outer space, and the data obtained by X-ray telescope conduces to investigating the basic physical law under the condition of extreme gravity and magnetic field, In this article, multi-layer telescope is designed to satisfy the demand for enhanced X-ray timing and polarimetry mission. in which the telescope is designed based on Wolter-I telescope. The Monte Carlo method and power spectral density are used when the relationship between mirror profile and roughness with angular resolution is investigated. We analyze the relationship between angular resolution and mirror profile, and the result shows that the higher mirror profile possesses higher angular resolution. When the root mean square(RMS) of mirror profile is 0.04 μm, PV is 0.2 μm and roughness is 0.4 nm, the mirror angular resolution is 6.3" and it will change to 30.6" when the RMS of mirror profile is 0.2 μm, PV is 1 μm and roughness is 0.4 nm. The angular resolution out of focus is also investigated in this article, and the more defocusing amount gives rise to the worse angular resolution because defocusing spot will be larger than that of focal plane. So the maximum defocusing amount of 5 mm is required when the focal plane detector is installed. The relationship between effective area with film structure and layers number is also investigated. The film with Au mixed with C has a higher reflectivity than the film with only Au, because the mixed film will generate an interference effect and enhance the intensity of reflecting X-ray. When the telescope layers increase, the effective area and telescope weight are both improved, the requirement for effective area of satellite can be satisfied when the number of nesting layers is 45. However, when the number of nesting layers further increase, the effective area will be improved with a low speed, but the weight of telescope will increase with a high speed. The field of view of this telescope is 16′, which is more than the required value of 12′. Finally, the X-ray focusing telescope with 5.25 m focal length, 45 nesting layers, effective area 842 cm<sup>2</sup> at 2 keV, 563 cm<sup>2</sup> at 6 keV is obtained.