Theoretical question about electromagnetic radiation...

[Jonsy123]

mezarashi wrote:

diffuse reflection is the one where you get an absorption followed by a re-emission.

 

Why is it called "diffused reflection" ?, maybe because the direction of the momentum is lost in the process ?, so the photons emitted come out in all directions, and hence cause a "diffused" effect (I know you said the momentum is conserved in both diffused and specular reflection, but maybe in "diffused" reflection, the direction of the momentum isn't conserved... otherwise, what does the word "diffused" stands for ?.).

 

mezarashi also said:

As for specular reflection... But it is true that (in this case) the photon isn't absorbed, and interacts with the mirror "from a distance" you can say.

(In this case I can understand how the direction of the momentum is conserved).

 

DQW wrote:

The photon is actually absorbed and re-emitted. It is absorbed by one of the conduction electrons..

So, I guess DQW talked about diffused reflection ?...

[DQW]

I'm not sure what mezarashi means by this interaction "from a distance". I am talking about specular reflection - which, if I'm not mistaken (and I could be), is not empirically different from diffuse reflection at the microscopic scale. Diffuse reflection, in my opinion, is merely a macroscopic effect arising from surface topographical features.

 

For a metal, the Fresnel reflectance is essentially a constant (angle independent), and reduces to Snell's Law. Also, for a metal, one can easily derive Snell's Law from a simple calculation based on the Maxwell Equations (and angle conservation comes directly from requiring that the tangential component of the E-field be continuous at an interface). However, this classical explanation provides little intuition for the mechanism at a microscopic level. As you refine your models and go from a classical model to QM to QED..., you have different explanations that approximate the real phenomenon to different extents.

 

For a simple semiclassical treatment, see Feynman's Lectures Vol 2 Ch. 32.

Also see http://en.wikipedia.org/wiki/Plasmon