X-Ray Burning Lens: Why Can't it Focus?

[lufc88]

I know that High-energy (hard) X-ray light cannot be focused as easily as visible light by using a burning glass. But why is this? If there was x ray light spread over a normal sized lens with the same intensity as sun light why couldn't it focus? would the material needed for say 50cm^2 magnifying glass light focuser object need to be special?
could very intense radio waves in the same manner be focused over the same area or any other em waves?
whats special about sunlight?

 

[UltrafastPED]

The index of refraction for x-rays in glass is very close to 1; thus you cannot form a converging lens for this case.

A common technique is to use a crystal that is bent - the x-rays that are diffracted by the crystal structure are "captured" along the selected crystal paths ... and exit where you want them.

You can also use glancing incidence reflection, but the angles are very low ... both techniques are used in this paper which discusses the theory and experiment:
https://www.uni-due.de/agbovensiepen/Publikationen/REVSCI99.pdf

 

[UltrafastPED]

whats special about sunlight?

Glass is transparent for only part of the electromagnetic spectrum; for ordinary glass it absorbs starting in the UV at one end, and the infrared at the other.

You need to select the correct materials for part of the spectrum. Even then each wavelength will have a slightly different focal length: http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/aber2.html

 

[sophiecentaur]

There is not, ifaik, any substance that will behave, for X rays, the same as glass does for light - i.e. have a high enough refractive index without high transmission loss. X ray telescopes use the oblique reflection on the surface of a metal surface. Rays hitting the metal at near normal incidence will penetrate the surface. The surface is part of a paraboloid, way off axis (up on one side of the paraboloid surface). This link shows how an image can be focussed, using several paraboloid surfaces. To get the image focussed correctly, they also incorporate hyperboloid reflectors.