Investigation on optical design of X-Ray focusing observatory

X-Ray focusing observatory is one of the most important equipments for X-Ray space observation, which is designed based on grazing incidence principle. The purpose of X-ray observation are detecting black hole of various size in outer space, and the data of observatory would help us investigate the basic physical law in condition of extreme gravity and magnetic field, In this article, Multi-layers telescope has been designed for the demand of enhanced X-Ray Timing and Polarimetry Mission. in which the observatory is designed based on Wolter-I telescope. Monte Carlo method and power spectral density had been used when the relationship between mirror profile and roughness with angular resolution are investigating, We have analysis the relationship between different angular resolution and different mirror profile, and the result shows that higher mirror profile shares higher angular resolution. When RMS of mirror profile is 0.04 μm, PV is 0.2 μm and roughness is 0.4 nm, the mirrors angular resolution is 6.3", and this value will change to 30.6" when RMS of mirror profile is 0.04 μm, PV is 0.2 μm and roughness is 0.4 nm. Angular resolution out of focus are also investigated in this article, and the more defocusing amount shares the worse angular resolution because focal spot out of focal will be larger than that of focal plane. So the maximum defocusing amount of 5 mm is required when the focal plane detector installed. The relationship between effective area with film structure and layers number are also investigated, film with Au mixed with C have higher reflectivity than film of Au only, because the mixed film will generate interference effect and enhance the intensity of reflecting X-ray. When observatory layers increase, effective area and observatory weight both improve, the effective area demand of satellite are satisfied when the layer of observatory is 45. However, when the layer of observatory continue increasing, effective area would improve with a low speed, but weight of observatory would increase with a high speed. The field of view of this observatory is 16', which is more than the demand of 12'. Finally, the X-Ray focusing observatory with 5.25 m focal length, 45 layers, effective area of 842cm2@2keV, 563cm2@6keV is obtained.