Wolter telescope

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A Wolter telescope is a telescope for X-rays using only grazing incidence optics. Visible light telescopes are built with lenses or parabolic mirrors at nearly normal incidence. Neither works well for X-rays. Lenses for visible light are made of a transparent material with an index of refraction substantially different from 1, but there is no equivalent material for x-rays. Conventional mirror telescopes work poorly in the X-rays as well, since the light hits the mirrors at near-normal incidence, where the X-rays are transmitted or absorbed, not reflected.

X-rays mirrors can be built, but only if the angle of incidence is very low (typically 10 arc-minutes to 2 degrees)^[1]. These are called glancing incidence mirrors. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror.^[2][3]. Not surprisingly, these are called Wolter telescopes of type I, II, and III. Each has different advantages and disadvantages.^[4]

[edit] References

1. ^ Kulinder Pal Singh. "Techniques in X-ray Astronomy". http://www.iisc.ernet.in/academy/resonance/June2005/pdf/June2005p15-23.pdf. 
2. ^ Wolter, H. (1952). "Glancing Incidence Mirror Systems as Imaging Optics for X-rays". Ann. Physik 10: 94. 
3. ^ Wolter, H. (1952). "A Generalized Schwarschild Mirror Systems For Use at Glancing Incidence for X-ray Imaging". Ann. Physik 10: 286. 
4. ^ Rob Petre. "X-ray Imaging Systems". NASA. http://imagine.gsfc.nasa.gov/docs/science/how_l2/xtelescopes_systems.html. 

[edit] See also

• ROSAT Orbiting X-ray observatory
• Chandra X-ray Observatory Orbiting observatory using a Wolter X-ray telescope.
• XMM-Newton Orbiting X-ray observatory using a Wolter Type-I X-ray telescope.
• Swift Gamma-Ray Burst Mission Contains a Wolter Type-I X-ray telescope