Guilin Sun
Ansys Employee

It seems such material and physics can be included in FDTD. thus the simulation accuracy depends on the mesh, PML and other settings.

For higher orders unexpected, it is because the amplitude of the origial signal is too high. you can either reduce the source amplitude, or reduce non-linear coefficient. Theory usually have assumptions. even with perturation chi*E2 is small, it does not guarantee no higher orders can occur.