PerspectiveImaging Techniques

Mapping bond orientations with polarized x-rays

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Science  30 May 2014:
Vol. 344, Issue 6187, pp. 969-970
DOI: 10.1126/science.1254902

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Good sunglasses eliminate glare because their surfaces have filters that pass only vertically polarized visible light. Reflected light from outdoor horizontal surfaces (a wet street or snow-covered ground) is horizontally polarized, and the crossed filter blocks this light. Many other interactions of light with materials depend on polarization. A birefringent material is an optically active substance that has a refractive index that depends on the polarization and propagation direction of light relative to the crystallographic axes of the material. Such a material can rotate the polarization direction of the incident light, and this effect can be used for identification of crystals in polarized light microscopy. On page 1013 of this issue, Palmer et al. (1) use an analog of this method that exploits the shorter wavelength of x-rays to identify regions of order and disorder on a smaller scale, the orientation of bonds in a crystal.