Optics: Light and it's interaction with matter

[~enigma~]

Just double checked my Optics book. You failed.

Can you quote it or give us a reference as to how I am wrong?

 

[technoextreme]

Nobody can say it is the same or different photon but lets watch the mental gymnastics techno tries.

Really now why don't you tell me why I am wrong because you were wrong about detecting single photons.

 

[nathan]

If you are using a laser beam its easy because any sort of remission will whack the coherency out. Then again I don't even think you can actually detect a single photon alone so the question is a bit rhetorical.

Individual photons can be detected. (and thus proved the wavelike property of photons is individual to a photon by showing diffraction occurring at that level)

Reemission may preserve coherency in some circumstances, this happens inside a laser for instance.

However, the earlier question of 'can you distinguish one photon from another' is no, not if the two photons are identical.

 

[nathan]

My understanding is that "detecting" a photon takes it out of the race and "it" cannot be detected somewhere else later

Yes, that's pretty much the case. Any measure of detecting the photon will alter it in some way (most likely by destruction).

 

[G O R T]

You are using the wrong terminology. If the light reemitted then it has been in fact absorbed by the material.

True as far as that goes.
Photons are absorbed and reemitted constantly through matter, this is what effectively slows the transmission as given by the refractive index. Thermal absorbtion is terminal to the photon and adds energy to the atom. Some of this energy may be reemitted as a photon again but it will be somewhere in the infrared.

If you are using a laser beam its easy because any sort of remission will whack the coherency out. Then again I don't even think you can actually detect a single photon alone so the question is a bit rhetorical.

Reemission occurs in the rod, the air, the lenses, and even the surfaces of the mirrors. The only place it does not is in vacuum. Single photons can be detected, but not their path (see slit experiments).

Ignore that previous post. I was wrong. You can in fact detect a single photon and your question can be answered without detecting one photon. Namely there are two ways to figure out whether or not the photon was remitted. It either comes out at a completely weird direction or in fact the frequency shifts ever so slightly (It is detectable). My one professor actually uses a technique to detect the photons that get scattered the least in the human body in that the quickest path between two points is the most direct which means they get scattered the least.

Reemitted photons do not change frequency unless they contain enough energy to destabilize an atom, or the atom contains sufficient energy to add some to the reemitted photon. Think higher X-rays or gamma rays and look up Compton scatter.

Other scatter happens due to random refraction incidence in a material or polarization from the electric field of particles in gasses. Scatter is very wavelength dependant (higher wavelengths scatter first).

 

[nathan]

True as far as that goes.
Photons are absorbed and reemitted constantly through matter, this is what effectively slows the transmission as given by the refractive index.

Why is the reemitted photon coherent with the absorbed photon?

 

[~enigma~]

Really now why don't you tell me why I am wrong because you were wrong about detecting single photons.

In case haven't (and it seems you haven't), reread the original post you responded to and this time notice that it says TEST.

 

[sol invictus]

AFAIK you can't detect a single photon nor can you "tag" one for later identification.

It's very easy to detect single photons - it's done routinely in optics labs, particle physics experiments, etc. Hell, even the photoreceptors in the human eye can detect them (but the mind filters signals from bunches with less than 5 or 10, since otherwise there'd be too much noise).

As for "tagging", that's impossible, just as it's impossible for all elementary particles. All photons of the same frequency are absolutely indistinguishable.

 

[nathan]

It's impossible, just as it's impossible for all elementary particles. All photons of the same frequency are absolutely indistinguishable.

.. same frequency and polarization (though you can't tell the difference between a photon of say up polarization, and a different photon that has now been rotated to up polarization). Depends on the precise setup