Suppose I want to try and guess the fields of a short laser pulse. We know that fields that satisfy Maxwell's equations minimize the action E^2 - B^2 (say far from charge and current)? For a plane wave E^2 - B^2 = 0? Will a general solution of maxwell's equations satisfy E^2 - B^2 = 0 If I have a set of fields (say the approximate solution given by Jackson above) can I be guaranteed that the action for the actual solution will be less then the action for the approximate solution? Can I consider E^2 the "kinetic" part of the energy and consider B^2 the "potential" part of the energy? Thanks for any help or suggestions!