Editing Zone plate (section)

===Physics===
There are many [[wavelength]]s of light outside of the visible area of the [[electromagnetic spectrum]] where traditional [[Lens (optics)|lens]] materials like glass are not [[transparency (optics)|transparent]], and so lenses are more difficult to manufacture.  Likewise, there are many wavelengths for which there are no materials with a [[refractive index]] significantly differing from one.  [[X-rays]], for example, are only weakly refracted by glass or other materials, and so require a different technique for focusing.  Zone plates eliminate the need for finding transparent, refractive, easy-to-manufacture materials for every region of the [[spectrum]].  The same zone plate will focus light of many wavelengths to different foci, which means they can also be used to filter out unwanted wavelengths while focusing the light of interest.

Other waves such as sound waves and, due to [[quantum mechanics]], matter waves can be focused in the same way.  Wave plates have been used to focus beams of neutrons and helium atoms.<ref name="wmm" />