Nonlinear optical analogies in quantum electrodynamics
  Some of the basic notions of nonlinear optics are summarized and then applied to the case of the Dirac vacuum, as described by the Heisenberg-Euler effective one-loop Lagrangian. The theoretical and experimental basis for the appearance of nonlinear optical phenomena, such as the Kerr effect, Cotton-Mouton effect, and four-wave mixing are discussed. Further effects due to more exotic assumptions on the structure of spacetime, such as gravitational curvature and the topology of the Casimir vacuum are also presented. 
D. H. Delphenich