In classical electrodynamics, light waves propagating in vacuum do not interact. However, in quantum electrodynamics (QED), physical vacuum possesses a weak nonlinearity described by the Euler-Heisenberg (EH) effective Hamiltonian, allowing photons to interact with each other. Furthermore, some of the well-motivated theories accounting for the dark matter content of the universe predict additional nonlinear terms with a distinct polarization dependence. Quantitative characterization of photon-photon interactions would therefore provide a window onto dark matter physics.
We use high-intensity laser fields to probe the electromagnetic nonlinearity of physical vacuum. This project takes advantage of the high-power focusing cavities originally developed for phase retardation of free electrons. The cavities resonantly enhance the interaction, potentially enabling detection of the EH nonlinearity in a tabletop experiment.