Photon interaction with atoms in transparent medias

In summary: Snell's law and forward scattering. In summary, forward coherent scattering only occurs for the light which obeys Snell's law while traveling through the material; Snell's law depends upon the angle of incidence, and the index of refraction for the materials (e.g., air-glass-air). So for any wave propagation passing from one material to another there is a "Snell's Law"; it is a property of waves, and the change in speed of wave propagation is a measure of "impedance" of the material. This impedance is due to "forward coherent scattering" which delays the phase-front due to interference effects from the different scattering sources (the Huyghens' wavelet mechanism). All
  • #1
Milad H
2
0
Dear All,
I have read many posts on this forums about the interaction of photons with the atoms of transparent materials. The point that I was searching for in particular was "why is the speed of light in transparent material less than c".
The explanations given by many about the absorption and re-emission of photons by the atoms are quite elaborate. However, there is no mention of scientific references for that theory.
Can anyone, please, provide me with some references where this theory is explained.
Thank you in advance for your help.
Milad H.
 
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  • #2
The book by Born and Huang, "Dynamical theory of crystal lattices" is one of the most careful and thorough discussions, but quite high brow. Seems to be available online:

http://www.chem.elte.hu/departments/elmkem/szalay/szalay_files/KvantKemSzemin/Max%20Born%20%20K%CA%BBun%20Huang%20Dynamical%20theory%20of%20crystal%20lattices%20%201954.pdf
 
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  • #4
Milad H said:
The explanations given by many about the absorption and re-emission of photons by the atoms are quite elaborate.

"absorption and re-emission" would result in missing spectral lines, and random loss of coherence because emission occurs at random times and directions. So let's start over:

For transparent substances (glass, air) we know that an image is propagated by the light passing through that material. For this to happen several things have to be true:

1. The waves must retain their relative phases (coherence)
2. The waves must travel in the forward direction (forward scattering)

Forward coherent scattering only occurs for the light which obeys Snell's law while traveling through the material; Snell's law depends upon the angle of incidence, and the index of refraction for the materials (e.g., air-glass-air).

For any wave propagation passing from one material to another there is a "Snell's Law"; it is a property of waves, and the change in speed of wave propagation is a measure of "impedance" of the material. This impedance is due to "forward coherent scattering" which delays the phase-front due to interference effects from the different scattering sources (the Huyghens' wavelet mechanism). All directions which are not the "forward" direction described by Snell's law result in destructive interference; in the forward direction you get constructive interference.

So inside the material the light travels at c, but due to the "forward coherent scattering" a geometric analysis shows that the effective speed of the phase front is reduced ... but once the light crosses out of that material the effects are determined by the new material (air after coming from the glass), and the light has a new characteristic speed. But all along it is traveling at c.

Richard Feynman explains this in more detail in "QED: The Strange Theory of Light and Matter".

You can find some more detailed information here:
http://www.ece.rice.edu/~daniel/262/pdf/lecture11.pdf

http://www.scribd.com/doc/27753743/C...ght-Scattering
 
  • #5
UltrafastPED said:
The section "45. Local treatment of optical effects", starting on p. 339?

No, it starts already in chapter 8 and basically, the whole book is dedicated to wave propagation in matter.

Not at variance with your scattering theoretic explanation of the problem I think that it is easiest to understand the problem in a purely classical setting. Namely a dipole driven by an electric field will lag behind the field and the radiation emitted by it will be somewhat out of phase. Hence repeated scattering will lead to a softening of the wave (i.e. a smaller wavelength than in vacuo).
 
  • #6
DrDu said:
No, it starts already in chapter 8 and basically, the whole book is dedicated to wave propagation in matter.

Not at variance with your scattering theoretic explanation of the problem I think that it is easiest to understand the problem in a purely classical setting. Namely a dipole driven by an electric field will lag behind the field and the radiation emitted by it will be somewhat out of phase. Hence repeated scattering will lead to a softening of the wave (i.e. a smaller wavelength than in vacuo).

I agree with above, that index of refraction is easiest to understand classically.
I would like to see a QM explanation also for the index of refraction.
 
  • #7
DrDu said:
The book by Born and Huang, "Dynamical theory of crystal lattices" is one of the most careful and thorough discussions, but quite high brow. Seems to be available online:

http://www.chem.elte.hu/departments...ynamical theory of crystal lattices 1954.pdf

Thank you all for your help. I already have Born's book, but to be honest it's quite complicated.
I found in Feynman's lectures a "gentler to the mind" version.
 
  • #8
morrobay said:
I agree with above, that index of refraction is easiest to understand classically.
I would like to see a QM explanation also for the index of refraction.

The QM version is similar to the classical ... the wave function interfers following the scattering events.
 

1. How do photons interact with atoms in transparent media?

When photons (particles of light) enter a transparent medium, they may interact with the atoms in several ways. The most common interaction is absorption, where the photon is absorbed by an atom and its energy is transferred to the atom's electrons. Another possible interaction is scattering, where the photon changes direction after interacting with an atom. Lastly, photons may also pass through the medium without interacting at all, which is known as transmission.

2. What determines the likelihood of a photon interacting with an atom in a transparent medium?

The likelihood of a photon interacting with an atom in a transparent medium depends on a few factors. One factor is the energy of the photon, which must match the energy required for the atom to absorb or scatter it. Another factor is the density of atoms in the medium, as more atoms means a higher chance of interaction. Additionally, the type of atom and its electronic structure also play a role in determining the likelihood of interaction.

3. How does the interaction of photons with atoms in transparent media affect the speed of light?

The interaction of photons with atoms in transparent media can affect the speed of light in that medium. When a photon is absorbed by an atom, it is temporarily stored as energy in the atom's electrons. This slows down the overall speed of light through the medium. However, when the atom releases the absorbed energy and re-emits the photon, the speed of light returns to its original value.

4. Can the interaction of photons with atoms in transparent media be controlled?

Yes, the interaction of photons with atoms in transparent media can be controlled in various ways. One method is by changing the properties of the medium, such as its temperature or density, which can affect the likelihood of interaction. Another method is by using external fields, such as electric or magnetic fields, to manipulate the energy levels of the atoms and therefore control their interaction with photons.

5. Can the interaction of photons with atoms in transparent media be used for practical applications?

Yes, the interaction of photons with atoms in transparent media has many practical applications. For example, it is the basis for technologies such as laser technology, fiber optics, and solar cells. Understanding and controlling photon interactions with atoms in transparent media is crucial for developing and improving these technologies, as well as for advancements in fields such as telecommunications, medicine, and renewable energy.

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