In this paper (Link: http://aip.scitation.org/doi/abs/10.1063/1.4886409), the authors simulate third harmonic generation of gold by Lumerical FDTD solution.

They compare the third harmonic emission of different wavelength.

However, in the nonorm setting, the unit of the power after integrating the poynting vectors over the 2D monitor supposes to be W/Hz^2, so what I should do before I can compare the power of harmonic generation of different wavelength, like the case in this paper?

Thanks for any kind of help.