4
$\begingroup$

In Young's double slit experiment I put a convex lens after double slit and direct interference pattern on to a fibre. Then I expose the other end of fibre to a screen. What will I observe - the interference pattern (slightly jumbled) or a dot? Will photons behave as wave or particle?

$\endgroup$
1
$\begingroup$

This is not a particularly clean experiment. Be careful.

First, study up on Fourier Optics: http://www.amazon.com/Introduction-Fourier-Optics-Joseph-Goodman/dp/0974707724 . This tells you that you can't just put an arbitrary lens in front of the double slit.

I assume you are putting the fiber at the back focal plane of the lens. This is essentially the Fourier transform of the double slit and the fiber samples this irradiance pattern.

Next, is this a SMF (Single Mode Fiber) or a MMF (Multimode Fiber)? See http://www.amazon.com/Fundamentals-Optoelectronics-Clifford-R-Pollock/dp/0256101043/ref=sr_sp-atf_title_1_1?s=books&ie=UTF8&qid=1400043557&sr=1-1&keywords=pollock+optoelectronics. I assume based upon your question it is a SMF. In which case, it only captures light that matches the mode of the fiber. In other words, only a diffraction limited focused spot (roughly 8 um in diameter depending upon the fiber).

Finally, this is done all the time without any fun quantum effects. Everything from AWG's to non-diffraction limited coupling optics, to guided wave to fiber coupling encounters something like this. The confinement of a SMF is not sufficient to be relevant in a quantum mechanical sense. There are many quantum states and many photons involved.

If you used a photonic crystal or single photon emitter, you might be able to see something interesting. However, I doubt you'll see any particle / wave duality at home or in a standard research lab; it'll be all wave optics.

| cite | improve this answer | |
$\endgroup$
0
$\begingroup$

I believe you will observe a dot. The reason for this is that you interfered way too much with the photon's wavefunction, and essentially forced it to behave classically. This phenomenon is known as Quantum Decoherence.

| cite | improve this answer | |
$\endgroup$
  • $\begingroup$ Are you sure Quantum Decoherence is relevant here? I don't understand how. $\endgroup$ – user42733 Apr 5 '14 at 11:18
  • $\begingroup$ You essentially couple the photon's wavefunction with the wavefunction of the lens, and then the wavefunction of the fibre. You do not talk about just photons and environment anymore, but photons + environment + lens + fibre which alters you initial wavefunction substantially. $\endgroup$ – Constandinos Damalas Apr 5 '14 at 11:24
  • $\begingroup$ Right. So the fibre will alter it too, I didn't consider that. But finally, we'll still get an interference pattern right? A concentrated one, so it looks like a dot. $\endgroup$ – user42733 Apr 5 '14 at 11:28
  • $\begingroup$ It is hard to know without doing the experiment, but I believe you won't have an interference pattern $\endgroup$ – Constandinos Damalas Apr 5 '14 at 11:32
  • $\begingroup$ If it is concentrated one we can put a concave lens and observe it. Or simply record it on CCD without lens to know what happened in the end. If I get a chance to do this experiment I will definitely put the result here. It will be interesting because I am not sure wavefunction will get affected by glass or fibre. $\endgroup$ – user43794 Apr 5 '14 at 12:07
0
$\begingroup$

I think you will observe something which will look like a dot because the interference pattern will become too small to be observable (but it will be there). This doesn't mean that the photons will behave as particles.

| cite | improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.