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Refractive index in the ultraviolet region

  1. Jul 29, 2015 #1
    When white light is refracted in a prism, we can see that blue color has the strongest refraction: the shorter the wavelength, the strongest the refraction. But the electromagnetic radiation with very short wavelength (X-rays) are not refracted by an amorphous solid such as glass: most part of the radiation goes straight through the glass with no interaction.

    Since the behaviour is so different in the optical and the X-ray regions, I wonder what happens between both, i.e, in the UV region. Does the refractive index increase with the frequency of the wave until some point and then fall quickly, or what happens exactly?

    Thanks in advance!
  2. jcsd
  3. Jul 29, 2015 #2


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    This is in most cases not true, X-rays are well known to be easily absorbed by common medium, the absorption is due to the electronic transition in the medium that typically takes place within XUV and X-rays region.
    The refractive index profile is determined by the structure (e.g. the bonding types, crystal properties etc) of the medium, where there are transitions in the level structure, there can be found strong absorption. One of such regions is the UV region as explained above. Now absorption and refractive index are mutually-dependent quantity, in particular it can be shown that whenever there is an absorption peak, there will also be a region where anomalous dispersion takes place. In the refractive index graph vs frequency, anomalous dispersion is shown as a negative slope region.
  4. Jul 30, 2015 #3
    OK, I was inaccurate when I said that "most part of the radiation goes straight through the glass with no interaction", but I meant that the part of the X-ray beam that is transmitted through the glass (not absorbed or scattered) goes straight, does not undergoes any "deflection" like the light refracted in the prism. But I have just found out that X-rays can be refracted in the boundary between two media, it's just only that the refractive index is typicaly very very close to unity in that region of the spectrum and the deflection is tiny compared to ordinary light refraction.

    Could you attach or link any example of these graphs?
    Thank you!
    Last edited: Jul 30, 2015
  5. Jul 31, 2015 #4


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