The Vlasov susceptibility for two interacting electromagnetic waves is derived by using an extended version of the ‘‘κ–χ theorem.’’ The plasma is relativistic and magnetized. It is allowed for arbitrary k⊥ρ, ω/Ω, k⊥/k∥, and v/c. Nonuniformities in the background quasistatic magnetic field are also included. As an application, a general expression for the free‐electron laser susceptibility is derived.
Grebogi, C., & UHM, H. S. (1986). Vlasov susceptibility of relativistic magnetized plasma and application to free‐electron lasers. Physics of Fluids, 29(5), 1748-1749. https://doi.org/10.1063/1.865646