An instrument used to focus X-rays into an image. Most X-ray telescopes are grazing-incidence telescopes, based on a technique first developed in the 1940s and 1950s. A complete unit may combine a number of individual mirrors mounted concentrically, inside one another. The most commonly used types are Wolter telescopes. Since the mid-1980s normal-incidence X-ray telescopes have been developed, exploiting the reflecting properties of multi-layer coatings on conventional mirrors. However, their efficiency is restricted to only a very narrow wavelength range, determined by the particular coating used. More recent research has led to the development of micropore optics, which consist of a large array of small holes in a silicon wafer, with one wall of each hole being an X-ray reflecting surface. In all designs of telescope, the X-rays are focused on to an X-ray detector, such as a gas scintillation proportional counter, a proportional counter, a CCD spectrometer, or a microchannel plate detector.
Subjects: Astronomy and Astrophysics.