What happens when photons interfere?

[big314mp]

In a recent SciAm article (last month, I think) there was an article on geo-engineering. One proposal was to use perforated disks of a clear material arranged in a cloud between the earth and the sun. The premise was that light passing through the perforations would travel slightly faster than light passing through the disk material. The light would then destructively interfere on the other side, thereby reducing the amount of light falling on the Earth.

 

My question is: What happens to the energy carried by the light? It obviously can't be destroyed, but where does it go?

[iNow]

My first thought is that it would heat the disk through which it passes, but I'm really not certain.

[swansont]

Destructive interference at one point will have constructive interference at some other point associated with it. Energy is conserved.

[thedarkshade]

My first thought is that it would heat the disk through which it passes, but I'm really not certain.

I think so too. Occasional collisions of pthtons with the material would result in transfering the energy to that material (heating hit), which energy of course would count in total energy.

[big314mp]

So I'm guessing the premise is to create a double slit type pattern of fringes, and then make sure a dark fringe lines up with the earth.

 

I found the article, btw:

 

http://www.sciam.com/article.cfm?id=geoengineering-how-to-cool-earth&page=5

 

The way it's described makes me think the physics is a bit faulty though.

[danny8522003]

Would it not just reflect off the sunny side of the disk?

[Norman Albers]

I'll guess "yes" with danny..., along with absorption in the disk. It should be somewhat like my "fizziks" thread of reflections in the window.

[Norman Albers]

The issue was stated as having a "clear material" which is a slightly absorbing medium of some higher index of refraction. This defining statement says that "not much energy" will be absorbed. Then consider the many holes (like a honeycomb pattern presumably) which are air environments, and the interference of different paths.

Edited January 16, 2009 by Norman Albers

[Pete]

What happens when photons interfere?

Photons don't interfere. Waves do. To understand why it would be illustrative to think of a similar device which works with electrons rather than photons.

[swansont]

Photons don't interfere. Waves do. To understand why it would be illustrative to think of a similar device which works with electrons rather than photons.

 

Electrons interfere, too. Single photons interfere with themselves. One issue is trying to separate the concept of waves from that of photons. You can't. Light exhibits properties of both. As do electrons.

[Norman Albers]

Single photons interfere with themselves.

Could you elaborate on this?

[Klaynos]

Could you elaborate on this?

 

A double slit experiment, set-up in the normal way. But instead of using a laser incident on the slits and creating an interference pattern, you have a single photon source, which emits a single photon at a time. You allow this to run for say 1000 single photons, and the pattern on the detection plate is an interferon pattern, the only way this is possible is if a photon interferes with itself and in fact travels through both slits at once.

[Norman Albers]

Doy, doy, I am just waking up. Thanks. In a faraway forum in a distant galaxy I learned that up to very high energies, two photons do not interfere or scatter. At some high energy they do and this puts a limit on their populations. Do folks here agree?

[swansont]

IIRC — photon scattering a second-order interaction, so it doesn't become important until high energy. But interference is not the same thing, and happens readily at all energies.

[Norman Albers]

You may recall me asking how far apart two "slits" may be? Along the same lines, what am I to make of the description (Feynman) of the probability of a photon to be emitted into a (small) differential solid angle?

[Norman Albers]

Could we create two entangled photons and then recombine them, with the same path length, to get interference?

[swansont]

Could we create two entangled photons and then recombine them, with the same path length, to get interference?

 

Yes

 

http://sciencelinks.jp/j-east/article/200314/000020031403A0470732.php

 

We have investigated the two-photon diffraction-interference of entangled photon pairs generated by optical parametric down-conversion.

[Norman Albers]

Verrrry niiiice, thank you! Hey big314mp, I read somewhere that if you are trying to shield noise like from a neighbor banging a gong, drilling holes in your otherwise solid wall can enhance the filtering of transmissions. This is what you were snooping after...

Edited February 28, 2009 by Norman Albers