The dynamics of the SFG polarization sources, Visualization 4(e), can be very closely approximated by a combination of the first three modes of the nanorod excited in the linear regime, i.e. the modes (1,2), (2,2) and (3,2), Fig. 4 (a-c). This is obtained by summing the complex-valued distributions of the electric field just below the surface of each eigenmodes and then squaring the resulting fields. The time dependence is realized by varying the phase of the fields. The separate eigenmodes, their sum and their sum squared are shown in Visualization 4(a-e). The colors represent the magnitude and direction of normal electric field distribution associated with the eigenmodes of the sphere, blue for electric field pointing from background to metal and red for the opposite direction. For the Visualization 4(e), the electric field is squared leading to the polarization pointed always away from the nanostructure.