If we shoot to photons to a surface, in which conditions we can differentiate the points where the photons collided with the surface?

Question

Now, I heard this example from one of my professor 4 years ago when I first entered university, and at that I had some objections (and I still do), because, I think, if we flick our wrist fast enough, the spot on the moon will not be a continuous spot, but that spot will be like "$. \quad .\quad . \quad . \quad .$", as if we as turning on and off the light while moving it, and these ideas led me to the following question:

Lets shoot a two photon onto a reflective surface, and observe where the photons hit the surface;

What conditions should be satisfied so that we can differentiate the points where the photons collided with the surface ?

score 1 · Accepted Answer · answered Jan 23 '19 at 12:40

Look at this experiment where photons hit a sensitive "screen".

On the left it is the footprints of individual photons in a dxdy interval. The condition that is satisfied is that the individual photon's energy raises a photosensitive interaction which can be recorded. The accumulation gives the usual classical interference pattern of light in this geometry.

In this experiment the photon energy is absorbed. One could use a different one where the photon would compton scatter and again leave a foot print but there is no reason to do so.

Light is composed out of zillions of photons and forms a continuum . To get at your ". . ." on the moon one would have to use single photons as in the experiment above

If we shoot to photons to a surface, in which conditions we can differentiate the points where the photons collided with the surface?

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