Development of lightweight x-ray mirrors using carbon fiber reinforced plastic and ultra-precision machining technology

Lightweight X-ray telescopes with high-angular resolution and a large effective area are essential for elucidating the physical mechanisms behind the evolution of super-massive black holes. To achieve such X-ray telescopes, we are developing X-ray mirrors using carbon fiber reinforced plastic (CFRP); CFRP is a lightweight but strong material that can be processed into a variety of shapes. However, CFRP has a finely textured surface, known as print-through, which is too rough to reflect X-rays effectively. To mitigate the print-through issue, we developed a method to form a thin amorphous nickel phosphide (NiP) layer on the surface of CFRP. The NiP surface was then finished using ultra-precision machining technology to achieve the required surface roughness for X-ray reflection. We fabricated a CFRP plane mirror, and an X-ray reflectivity measurement for the plane mirror using the ISAS X-ray beam line confirmed that the surface roughness was approximately 1.5 nm. Additionally, we made a Wolter-I type mirror and demonstrated that it could focus X-rays. However, the half-power width of the reflected X-ray image was 9.6 arcmin.