Resonant generation of high-order harmonics in nonlinear electrodynamics

We study the process of resonant generation of high-order harmonics in a closed cavity in the model of vacuum nonlinear electrodynamics. Concretely, we study the possibility of resonant generation of the third harmonic induced by a single electromagnetic mode in a radiofrequency cavity, as well as resonant generation of a combined frequency mode induced by two pump modes ($\omega_1$ and $\omega_2$). We explicitly show that the third harmonic as well as the $2\omega_1+\omega_2$ combined frequency mode are not resonantly amplified, while the $2\omega_1-\omega_2$ signal mode is amplified for certain cavity geometry. We discuss the process from the point of view of quantum theory.