Are Photons Reflected Directly from Surfaces or Re-emitted by Atoms?

[JR Wakefield]

Simple question. Are photons reflected as is from a surface like a mirror, or is the reflecting surface atoms capturing the photons and re-emitting them?

 

[haruspex]

Simple question. Are photons reflected as is from a surface like a mirror, or is the reflecting surface atoms capturing the photons and re-emitting them?

Certainly not capturing and re-emitting in the sense of electrons changing energy levels. In that process, the new direction would be random.
Reflection is more easily envisioned with the wave nature of light.

 

[Dale]

Are photons reflected as is from a surface like a mirror, or is the reflecting surface atoms capturing the photons and re-emitting them?

There are surfaces called diffraction gratings. They can cause photons to reflect at an angle different from the angle of incidence. They are used to show that reflection is not an interaction of a photon with a single atom, but with the entire surface. The photon doesn’t just take one path and interact with the one atom at the apex of that one path. The photon takes all of the possible paths and interacts with all of the atoms in a way that cannot be identified with any single atom of the diffraction grating.

 

[haruspex]

There are surfaces called diffraction gratings. They can cause photons to reflect at an angle different from the angle of incidence. They are used to show that reflection is not an interaction of a photon with a single atom, but with the entire surface. The photon doesn’t just take one path and interact with the one atom at the apex of that one path. The photon takes all of the possible paths and interacts with all of the atoms in a way that cannot be identified with any single atom of the diffraction grating.

But how can we know that this is the same mechanism as reflection from a mirror?

 

[Dale]

But how can we know that this is the same mechanism as reflection from a mirror?

A diffraction grating is just a mirror with blacked out stripes. The same laws of QED that describe the behavior of a diffraction grating also describe the behavior of a mirror without the black stripes.

 

[haruspex]

A diffraction grating is just a mirror with blacked out stripes.

Ok.

 

[ZapperZ]

Simple question. Are photons reflected as is from a surface like a mirror, or is the reflecting surface atoms capturing the photons and re-emitting them?

It is always problematic if you take a solid, but then start to consider its behavior in terms of the individual atoms. This is why solid state physics is different than atomic physics. There are no energy bands in an atom, but there are such bands in a solid.

There are several things to consider in the typical specular reflection of visible light off a typical mirror:

1. Angle of incidence = angle of reflection

2. There is a π phase shift of the reflected light

3. The "reflector", i.e. the mirror, is typically a smooth metal surface. A dielectric does not make a very good mirror.

Here's what we know:

1. An atom that absorbs a photon and then re-emits it, typically will not re-emit in a specific direction. So accounting for "angle of incidence = angle of reflection" will be extremely difficult. So that explanation that it is due to surface atoms absorbing and re-emitting is not very plausible.

2. Metals have conduction electrons, as opposed to dielectric/insulator. They should play a role in this optical process (and they do).

Zz.

 

[jtbell]

A diffraction grating is just a mirror with blacked out stripes.

Or a mirror with a “sawtooth” profile.

 

[JR Wakefield]

Thanks to all for replying. I already knew the answer. But simple things like your reflection in a window, or the road reflection off the asphalt at very low angles, and even prisms, shows photons bounce off surfaces.

 

[haruspex]

the road reflection off the asphalt at very low angles

Are you referring to the mirage produced by the thermal gradient of the air?

 

[ZapperZ]

Thanks to all for replying. I already knew the answer. But simple things like your reflection in a window, or the road reflection off the asphalt at very low angles, and even prisms, shows photons bounce off surfaces.

You started off by asking for a smple reflection off a mirror! Now you're changing the parameters.

I didn't say that ALL types of reflection are governed by the same process. The case for Bragg reflection off crystal lattice planes has already been mentioned. You asked for a specific case, you got a specific answer relevant to that case. It was not meant to be used where it doesn't apply.

Zz.