Xray refraction and UV refraction border?

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    Refraction Uv Xray
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SUMMARY

The discussion centers on the refraction indices of X-rays and ultraviolet (UV) light, highlighting that X-rays have a refraction index slightly below one, while certain materials exhibit a refraction index above one for UV light. The threshold for this transition is linked to the material's permittivity and its polarization response, particularly electronic polarization, which is effective up to approximately 1015 Hz. The relationship between plasma frequency and transparency to X-rays indicates that materials become transparent above their plasma frequency, resulting in a refraction index of less than one. The conversation suggests that further exploration of dielectric mechanisms and plasma frequency is essential for understanding these phenomena.

PREREQUISITES
  • Understanding of permittivity and its role in material response to electromagnetic fields.
  • Familiarity with plasma frequency and its implications for material transparency.
  • Knowledge of dielectric mechanisms, particularly electronic polarization.
  • Basic concepts of refraction indices and their significance in optics.
NEXT STEPS
  • Research the relationship between plasma frequency and refraction indices in various materials.
  • Study the mechanisms of electronic polarization and their frequency limits.
  • Examine the effects of different wavelengths of UV light on material transparency and refraction.
  • Explore advanced optics techniques for focusing short-wavelength UV light.
USEFUL FOR

Physicists, optical engineers, and materials scientists interested in the behavior of light in different spectral regions, particularly those studying X-ray and UV interactions with matter.

Artlav
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Xray in any matter have a slightly below one refraction index.
Ultraviolet still have materials with above 1 refraction index.

Where in the spectrum between them does >1 index cease to be possible, and what is the nature of this threshold?
 
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I think I've found some clues.

First thing is about permittivity.
A material can not polarize instantaneously in response to an applied field, which suggest that there should be a maximum frequency at which it would be able to.
This seems to be related to plasma frequency, but i can't find much on the values and cross-reference.

Then, there are several kinds of dielectric mechanism - electronic polarization seems to be centred around visible and UV, with nothing else above it, and it loses its response at around 10^15 Hz, which seems to be close to the right zone.
With no polarization response there would be no slowing phase velocity, and thus no >1 refraction.

Now, since the materials seem to become transparent to x-rays above their plasma frequency, and that waves in electron plasma can have phase velocity higher than c, we would see <1 refraction index.

However, 300nm seems to be a little too long a limit - well in the UV, while much shorter UVs can still be focused by regular optics.

Needless to say, I'm quite out of my depth already.
Does that make any sense, and is it the right direction to look in for the answer?
 

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