Distance between photons?

Photons are bosons, which means that you can have as many photons in the same state as you want. This means that an arbitrary number of photons can be in the exact same place, moving in the exact same direction with the same polarization.

In a laser, we try stack as many photons on top of each other in as small a space as we can. The density of photons that we get depends mostly on the technical limitations of the laser.

 

A laser disperses because of the motion of a single photon* not because photons bump into each other. Photons can pass right through each other and lie on top of each other without feeling each other at all (they only interact through gravity as far as we can tell)

* a laser disperses because a single photon is a wave... it also has a definite position - those are very vague statements, do not ponder them for too long, they will drive you mad unless you learn more about them

 

The point LukeD is trying to make, is that if you have a strong enough beam e.g. laser light, there is zero distance between them - they overlap. You can in principle even have what "looks" like a single photon, that actually is 2 photons overlapping completely - just twice as "strong".