# What happens when the frequency of light propagating through a solid equals the resonance frequency of the electrons in the atoms? [closed]

During the propagation of light through a solid, the photons collide with the atom making the electrons vibrate. What happens when the frequency of the light equals the resonance frequency of the electrons? Do all electrons have the same resonance frequency?

## closed as unclear what you're asking by Kyle Oman, ACuriousMind♦, Ryan Unger, Martin, Kyle KanosAug 29 '15 at 14:21

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• Welcome to Physics.SE! I removed the second link as it doesn't seem to add anything to the question. Also, it's a small stylistic thing, but the quote block (>) is meant for quoting other text rather than highlighting your question. – Kyle Oman Aug 26 '15 at 16:59
• Also, the article you link seems to answer your question reasonably clearly. What is it you didn't understand? – Kyle Oman Aug 26 '15 at 17:00
• I understand that when light passes trough a solid that passage is delayed by the interactions between the photons and the atoms. That interaction is basicly the vibration of eletrons at a given frequency (is it the frequency of the radition?) right? The text said that if the frequency of the light did not match the ressonance frequency of the eletron, photons would be reemited. So what i still don't understand is what if the frequency is equal? Does the photon imprisioned within the athom making the eletron vibrate permanently? – Gonçalo Couto Aug 27 '15 at 10:58

When there is a resonance in electron response, both refractive index and absorption change rapidly: the refractive index has a "jiggle" in the vicinity of the resonance, like this sketch (adapted from this earlier answer by John Rennie - but I disagree with the "n=1" label so I cut it off...:

As you can see there is higher refractive index at the low frequency end of the resonance).

At the same time, there is a peak in absorption at the resonance (since the electrons move more vigorously there is more coupling of the energy of photons with the solid).

Not all electrons have the same resonant frequency - it depends on how they are bound, and what their environment looks like. Also there is the problem that no two electrons can be in exactly the same state (Fermi exclusion) which also implies a (very) small amount of energy splitting.

Why does the refractive index depend on wavelength?

Why do prisms work (why is refraction frequency dependent)?

• There is the possibility that the electrons have a collective resonance frequency: Plasma oscillations in conductors. (I did not read the linked article, but this seems relevant to me for a complete answer to the question). – Sebastian Riese Aug 26 '15 at 21:03
• The change in the refraction index will simply make light "bend" more (the angle of refraction will increase in that particular area)? The peak in absortion will elevate the eletrons in level of energy locally and or cause eletron removal ? – Gonçalo Couto Aug 27 '15 at 11:08