fEnergy = energy() - assuming pulse is in vacuum
 fEnergy = energy(fMaterialRefractiveIndex) -
 1D-T (XY Gauss assumed)
 2D-TX (Y Gauss assumed)
  the energy in Joules contained in the grid
 
 
  TODO: in future go to \int |sqrt(n(omega))E(omega)|^2 dt and
  use the Perseval theorem so that the energy is estimated
  better.