# Single photon double slit experiment: why they don't get absorbed in the separation?

1. Feb 13, 2010

### alex440

hi
maybe i'm asking a stupid question, i'm a layman, and i didn't succeed to google out the answer.

while performing single photon double slit experiment,
why the photons don't just get absorbed in the separation between the slits, like they do in the screen behind.

and consequently, what is the maximum width of the slit so we keep seeing interference pattern.

in typical experiment the wavelength is around 0.5 $$\mu$$m and the separation is around 25$$\mu$$m, which is 50 times wider.

the only answer i found on the topic is this: http://www.physforum.com/index.php?showtopic=7209", but it's hard to comprehend

thanks

Last edited by a moderator: Apr 24, 2017
2. Feb 13, 2010

### Staff: Mentor

Re: single photon double slit experiment: why they don't get absorbed in the separati

Most of them do get absorbed not only by the material that separates the slits, but also by the material surrounding the slits.

Take a laser beam and shine it on a wall. You get a bright spot on the wall. Now put into the beam an opaque slide with two narrow slits that are separated by less than the diameter of the beam. The resulting interference pattern is much fainter than the original spot.

3. Feb 13, 2010

### alex440

Re: single photon double slit experiment: why they don't get absorbed in the separati

hi jtbell

well, you mean that single photons are not going the same line, each one is going at a different angle, or in different parallel lines.

those of them who are absorbed, we "lose" them, but those who don't, their wavefunction appears at the both slits.

so that if we'd close the slits, we'd see it absorbed at the place of the left or the right slit, but not at the center.

or, if we'd manage to fire protons with exactness comparable to the slits geometry, we'd get the interference only when we fire them directly in the direction of one of the slits, but not into the the separation.

say, we fire a photon in the direction of the right slit. we fire it from the middle between the slits, at a considerable distance.

in this case, after we fire a photon, his wavefunction probability is 100% on the right slit and 0% on the left slit (as at each other point in space)

but the function itself exists, and does not collapse, since his state did not change.

so the left slit alters the function in such a manner, that it behaves like it has 2 sources now, and it can interfere with itself.

the function collapses only if it has a subject to contact in a nonzero probability location. and it will collapse only in a number of cases predicted by a probability in this location.

thanks a lot.

Last edited: Feb 13, 2010