Photon radius and affected energy in double-slit experiments

[gnarlan]

Hi all, these questions have nagged me for years and I have never found a text or a paper that even addresses them.

Regarding photon "radius", what is the maximum width that two slits can be spaced which still permits the double-slit phenomenon to occur? Would this be a valid method of determining photon "radius"? Additionally, is that maximum width dependent upon frequency or is it the same for all photons?

Relatedly, if at any point beyond the slits, we attempt to observe the photon, we of course lose our interference pattern. But, does the photon that arrives at the photosensitive sheet possesses the same energy-momentum as the "pre-split" photon?

I appreciate any insight from you experimenters our there :) Cheers.

 

[Bill_K]

A photon does not have a "radius". It is the quantized version of a classical wave packet, and its size depends on how close the wave is to a pure plane wave. To obtain coherence over a larger distance you want a smaller spread in frequency and propagation vector. Experimentally this is determined by the quality of your laser.

The photon, when it reaches the screen, has the same frequency it started with, and the same energy.