[Users] How to add external fields to a simulation?

All,   I have been stydying the par files that are provided, but can't seem to figure out how to add an external scalar, spinor, or vector field to the simulation.  Specifically, I am interested in periodically sweeping a polarized electromagnetic plane wave across a simulation volume, from a source point that is outside the simulation volume.  I am also curious about permeating a volume with a bispinor field.  Is there a package that I would have to add?   Regards,   Ben Bernard