1：Experimental Design and Method Selection:

The simulation of the electric field was performed using a conventional FDTD method (FDTD Solutions, LumericalTM). A

2：5 μm × 5 μm metal film of a thickness of 200 nm was prepared with a nanohole of 10 nm positioned at its center. A five groove structure with a depth of 5 nm and having the form of a bull’s eye pattern was prepared surrounding this nanohole. Sample Selection and Data Sources:

A simulation volume having a width and a length of

3：5 μm to completely cover the metal film and a depth of 20 μm was prepared. A light source having a plane wave form and having dimension of 5 μm × 5 μm with parallel polarization was positioned 10 μm away from the film. List of Experimental Equipment and Materials:

FDTD Solutions software by LumericalTM was used for simulations.

4：Experimental Procedures and Operational Workflow:

Monitors having dimensions of

5：5 μm × 5 μm were positioned at the film surface and at distance from 1 μm to 10μm from the surface 1 μm steps. For precise the measurement, minimum mesh size was set as 1 nm. For the transmission spectra, the wavelength of the source was varied from 400 nm to 800 nm in steps of 5 nm. Data Analysis Methods:

The amplitudes of the Poynting vector spectrum was obtained at different monitor positions to investigate how the spectrum evolves while moving on the transmission side.