Photon-Photon Coupling (Gamma-Gamma)

[sanman]

So I've read that at sufficiently high energies, photons will interact with each other rather than passing through each other in the usual ghostly ways.

So in these situations, is constructive/destructive interference still possible? What is the threshold where it might stop, for practical purposes? (ie. what frequency or photonic energy level?)

Is there some energy where 2 photons would collide like hadrons would?

Is this type of coupling purely due to EM potential, or is there anything analogous to Pauli Exclusion Principle that could happen?

 

[PeterDonis]

I've read

Can you give a specific reference? That always helps.

at sufficiently high energies, photons will interact with each other rather than passing through each other in the usual ghostly ways

More precisely, there is an amplitude for photons to interact with each other, but it's way too small to observe at everyday energies and only becomes significant at high energies. One way to think about what is going on is to think of the interaction as involving the temporary creation of an electron-positron pair: a pair of incoming photons turns into an electron-positron pair, then the pair annihilates and creates a pair of outgoing photons. To us this looks like two photons interacting with each other (because we don't observe the temporary electron-positron pair), but of course there has to be enough energy to create the electron-positron pair (more precisely, to have a significant amplitude for pair creation) for the interaction to be significant.

in these situations, is constructive/destructive interference still possible?

It's always possible; it's a fundamental feature of quantum amplitudes.

Is there some energy where 2 photons would collide like hadrons would?

I don't understand what you mean. The interaction involved is the electromagnetic interaction, not the strong interaction.

Is this type of coupling purely due to EM potential

I'm not sure what you mean here either. It's the quantum electromagnetic field.

is there anything analogous to Pauli Exclusion Principle that could happen?

No, because there are not multiple fermions of the same type present.