fotonfotonsamverkan

fotonfotonsamverkan refers to the interaction between two photons, a process that is forbidden in classical electrodynamics but permitted in quantum electrodynamics (QED). In this framework, the interaction proceeds via virtual electron–positron pairs that temporarily emerge due to vacuum fluctuations. The lowest–order contribution to photon–photon scattering is encoded in the Euler–Heisenberg effective action, which describes nonlinear corrections to Maxwell’s equations at energies much lower than the electron mass.

The cross‑section for photon–photon scattering is extremely small; for visible light photons the predicted value is on the order of 10⁻⁵⁹ cm². As a result, the phenomenon has not yet been observed directly in ordinary optical experiments. However, high‑intensity laser facilities, such as those employing petawatt‑class beams, are approaching the regime where the probability of photon–photon scattering could be measurable. Experiments using intense gamma‑ray beams from synchrotrons and free‑electron lasers in combination with ultra‑intense laser pulses have set increasingly stringent experimental upper limits on the cross‑section.

Besides elastic scattering, photon–photon interactions give rise to phenomena such as photon splitting, photon merging, and the generation of photon pairs in strong electromagnetic fields. These processes are relevant for astrophysical environments with extreme magnetic fields, like magnetars, where QED vacuum birefringence and photon–photon scattering can modify radiative transfer and polarization signatures.

Theoretical investigations extend beyond QED, exploring photon–photon interactions in theories with extra dimensions, supersymmetry, or non‑commutative spacetime. In these extensions, additional virtual particle loops or modified dispersion relations can alter the effective coupling between photons, providing potential windows into physics beyond the Standard Model.