In my Universe Today article Magnetic Fields in Inter-cluster Space: Measured at Last, I said:Leaving aside the TeV gamma-infrared or microwave part, for the moment, have any photon-photon collisions resulting in pair-production been observed (in a particle collider instrument perhaps)?A very neat [trick], one that relies on physics not directly tested in any laboratory, here on Earth, and unlikely to be so tested during the lifetime of anyone reading this today – the production of positron-electron pairs when a high energy gamma ray photon collides with an infrared or microwave one (this can't be tested in any laboratory, today, because we can't make gamma rays of sufficiently high energy, and even if we could, they'd collide so rarely with infrared light or microwaves we'd have to wait centuries to see such a pair produced).
I've found references to reports of such, using LEP, involving GeV photons, but the collisions seem to be "quasi-real". How do these results relate to the real collisions between TeV gammas (from blazars) and microwave (the CMB) or infrared (EBL) photons? And what does "quasi-real" mean anyway??
And what would you say are the prospects of observing pair-production from TeV-IR or TeV-microwave photon collisions, in a laboratory here on Earth?