Hello All, My question is "What is the relationship between nonlinearity and dispersion?" I know that all materials are dispersive in nature, but keeping that aside for a moment and thinking of an ideal material, can I have a nonlinear (2nd order to be exact) material which is nondispersive? (Refractive index does not change with frequency)? Iv been trying to implement such a material in a simulator, but Im not getting any second order nonlinear interactions such as SHG or OR when I use this material. The same simulation with dispersive materials gives SHG and OR. Can some one please tell me the reason for this? Thank you very very much.