Light in a medium - Question about the FAQ

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SUMMARY

The discussion addresses the behavior of light in solid mediums, specifically regarding its speed relative to the phonon spectrum. It confirms that light does not travel at the speed of c within a medium when its frequency is outside the phonon spectrum, often resulting in absorption and energy dissipation as heat. The interaction with electronic excitations, particularly in the ultraviolet range, is more significant than phonon interactions in the infrared for visible light. Overall, light is consistently slower than its speed in a vacuum across various mediums.

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In the FAQ section 'Do Photons Move Slower in a Solid Medium?', it says that light is slower in a medium when its frequency is beyond the phonon spectrum. So do lights that have frequency within that spectrum move at the speed of c, not being slowed down by the medium?
 
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bubblewrap said:
In the FAQ section 'Do Photons Move Slower in a Solid Medium?', it says that light is slower in a medium when its frequency is beyond the phonon spectrum. So do lights that have frequency within that spectrum move at the speed of c, not being slowed down by the medium?

No. There can be several outcomes for this depending on the nature of the material. The simplest being that the light tends to be absorbed and its energy dissipated via heat, i.e the material is opaque to this light. This is because there are vibrational modes of the material that correspond to the same frequency.

Zz.
 
Light is almost always slower than the speed of light in vacuum, also above the phonon spectrum. Especially, for light in the visible range, the interaction with electronic excitations in the ultraviolet is much more important than the interaction with phonons in the IR.
 

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