Difference between revisions of "X-ray focusing"

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[[X-rays]] interact weakly with matter and are thus difficult to focus. The x-ray [[refractive]] index of most materials is extremely close to 1.0, which means that refraction is extremely weak and the conventional kinds of optics used in visible-light optics (glass lenses, metal mirrors, polarizers, etc.) are not applicable. Nevertheless, a variety of tricks can be used to direct and focus x-rays.
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[[X-rays]] interact weakly with matter and are thus difficult to focus. The x-ray [[refractive index]] of most materials is extremely close to 1.0, which means that refraction is extremely weak and the conventional kinds of optics used in visible-light optics (glass lenses, metal mirrors, polarizers, etc.) are not applicable. Nevertheless, a variety of tricks can be used to direct and focus x-rays.
  
 
For instance, since x-rays undergo [[Refractive_index#Total_external_reflection|total external reflection]] at very shallow angles (grazing-incidence), one can use extremely flat materials to slightly reflect x-rays. For instance, silicon wafers coated with metal stripes are typically used to achieved the required flatness, while having a sufficiently large electron density so that the [[critical angle]] is reasonably large. Because these mirrors are being used at grazing-angles, the [[beam projection]] is quite large: x-ray mirrors must typically be 100 mm to 2 m in length along the beam. An x-ray mirror can be very slightly bent, in which case the curvature effectively acts as a focusing optic. (Note that the radius of curvature is typically 6-30 km!)
 
For instance, since x-rays undergo [[Refractive_index#Total_external_reflection|total external reflection]] at very shallow angles (grazing-incidence), one can use extremely flat materials to slightly reflect x-rays. For instance, silicon wafers coated with metal stripes are typically used to achieved the required flatness, while having a sufficiently large electron density so that the [[critical angle]] is reasonably large. Because these mirrors are being used at grazing-angles, the [[beam projection]] is quite large: x-ray mirrors must typically be 100 mm to 2 m in length along the beam. An x-ray mirror can be very slightly bent, in which case the curvature effectively acts as a focusing optic. (Note that the radius of curvature is typically 6-30 km!)
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* [http://www.xradia.com/technology/basic-technology/focusing.php Xradia tutorial]
 
* [http://www.xradia.com/technology/basic-technology/focusing.php Xradia tutorial]
 
* [http://en.wikipedia.org/wiki/Compound_refractive_lens Wikipedia: Compound refractive lens]
 
* [http://en.wikipedia.org/wiki/Compound_refractive_lens Wikipedia: Compound refractive lens]
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* Figure 2 in: Gene E. Ice, John D. Budai, Judy W. L. Pang [http://www.sciencemag.org/content/334/6060/1234 The Race to X-ray Microbeam and Nanobeam Science] ''Science'' '''2011''', 334 (6060), 1234-1239. [http://dx.doi.org/10.1126/science.1202366  doi: 10.1126/science.1202366]
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* Yoshinobu Nozue, Yuya Shinohara and Yoshiyuki Amemiya [http://www.nature.com/pj/journal/v39/n12/abs/pj2007168a.html Application of Microbeam Small- and Wide-angle X-ray Scattering to Polymeric Material Characterization] ''Polymer Journal'' '''2007''', 39, 1221–1237 [http://dx.doi.org/10.1295/polymj.PJ2007077 doi:10.1295/polymj.PJ2007077]
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* Satoshi Matsuyama, Naotaka Kidani, Hidekazu Mimura, Yasuhisa Sano, Yoshiki Kohmura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi [https://www.osapublishing.org/oe/abstract.cfm?uri=oe-20-9-10310 Hard-X-ray imaging optics based on four aspherical mirrors with 50 nm resolution] ''Optics Express'' '''2012''', 20 (9), 10310-10319. [http://dx.doi.org/10.1364/OE.20.010310 doi: 10.1364/OE.20.010310]
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* Takashi Kimura, Satoshi Matsuyama, Kazuto Yamauchi, and Yoshinori Nishino [https://www.osapublishing.org/oe/abstract.cfm?uri=oe-21-8-9267 Coherent x-ray zoom condenser lens for diffractive and scanning microscopy] ''Optics Express'' '''2013''', 21 (8), 9267-9276. [http://dx.doi.org/10.1364/OE.21.009267 doi: 10.1364/OE.21.009267]

Latest revision as of 16:50, 24 September 2015

X-rays interact weakly with matter and are thus difficult to focus. The x-ray refractive index of most materials is extremely close to 1.0, which means that refraction is extremely weak and the conventional kinds of optics used in visible-light optics (glass lenses, metal mirrors, polarizers, etc.) are not applicable. Nevertheless, a variety of tricks can be used to direct and focus x-rays.

For instance, since x-rays undergo total external reflection at very shallow angles (grazing-incidence), one can use extremely flat materials to slightly reflect x-rays. For instance, silicon wafers coated with metal stripes are typically used to achieved the required flatness, while having a sufficiently large electron density so that the critical angle is reasonably large. Because these mirrors are being used at grazing-angles, the beam projection is quite large: x-ray mirrors must typically be 100 mm to 2 m in length along the beam. An x-ray mirror can be very slightly bent, in which case the curvature effectively acts as a focusing optic. (Note that the radius of curvature is typically 6-30 km!)

Focusing Optics

  • Mirrors: Grazing-incidence mirrors that are slightly curved in order to focus the x-ray beam.
    • Kirkpatrick-Baez Mirrors: Two mirrors oriented at right angles.
    • Wolter Mirrors: Can be used to form images of extended (non-point-source) objects. Cylindrically symmetric mirrors.
  • Capillary optics: Bundles of light-guiding pipes/capillaries can be used to focus.
  • Compound Refractive Lenses (CRL): Sequences of curved interfaces, to accumulate refractive effects and achieve focusing. (c.f. CRL)
  • Fresnel Zone Plates (FZP): Use diffraction effects (from rings of progressively different spacing/size) to focus beam.
  • Laue lens: Uses Bragg diffraction in order to focus beam (usually using a tilted crystal). Multilayer Laue lenses (MLL) can be used as effectively 1-D half-linear-zone-plates.
  • Kinoform lenses: Combine refractive and diffractive designs. (c.f. Detlef Smilgies presentation)

See Also

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