We are interested in probing CP Violation (CPV) in photon-photon interactions. Such interactions, effectively described by operators of the form FFFF ̃, have yet to be directly constrained experimentally, and could point to new sources of CPV beyond the Standard Model (SM). One possible mediator of CP-violating photon-photon interactions could be the relaxion, which is theoretically motivated within a dynamical solution to the Hierarchy problem, and is expected to interact with the SM both through axion-like and scalar Higgs-portal couplings. We propose a method for isolating CP-violating non-linear electrodynamics using Superconducting Radiofrequency (SRF) cavities, thus eliminating the main SM background, related to the CP-conserving Euler-Heisenberg (EH) Lagrangian.