Calculating scattering cross sections in the near field: Analytic proof and numerical verification

Highlights: ► Currently scattering cross section (SCS) is often calculated in the far-field. ► We proved analytically that the SCS can be calculated in the near-field. ► We carried out numerical simulations to verify our theory. ► We verified the SCS calculated in the near-field is equal to that calculated in the far-field. - Abstract: The scattering cross section (SCS) is a key property in plasmonic studies that carries valuable information on the scattering dynamics. Due to the complexity of fields and the interference from evanescent waves in the near-field region, the SCS is currently calculated in the far-field, which makes the computation costly. In this study we prove analytically that the total SCS is independent of the distance between the closed surface used to calculate the SCS and the scattering structure, hence introducing a numerically inexpensive approach to computing the total SCS, based solely on near-field information. We carry out also two numerical tests of this analytical proof in discretized spaces, verifying its applicability in computations