How to Correctly Obtain the Surface Plasmon Resonance of the object on Substrate

fdtd

#1

I’m currently researching on a nano-scale objects’ surface plasmon resonance when its on the substrate as a light shining on. However, I don’t know how to set the TFSF, scattering cross section, and the boundary condition correctly to obtain the result. Also, why does TFSF has a region unlike the plane wave? The simulation are indicated in the picture

In addition, when I was using the plane wave source with wavelength range to test the field enhancement result. I encountered 2 problems: 1. when I set different wavelength range, the field enhancement changes at every wavelength point, which is unphysical. 2. I follow the procedure to set the xy to periodic and z to PML, but the warning occurs?

Could someone help me figure it out? I will be very appreciated.


#2

Hi @z54gao,

The Total Field Scattered Field source is very specific, as it allows to separate the computation region into two distinct regions – one contains the total field, the other one the scattered field. The region defined by the TFSF source shows these 2 regions. Inside the TFSF box, you get the total field, outside you get the scattered field only.

To see how to set it up, you can check the correct usage page. In most case, when you use a TFSF source, you set the boundary conditions to PML. The plane wave is meant to be used with periodic boundaries. If you use a plane wave with PML, you will get some edge effects.

Regarding the problems you encountered:

  1. Changing the wavelength range can affect the simulation, as it can affect the mesh used in the simulation. If you are using the default setting (non uniform mesh defined by the mesh accuracy parameter, in the FDTD region), the mesh algorithm is trying to target a certain number of mesh cells per wavelength, so if you change the wavelength, it will change the target. Changing the wavelength range can also affect the material fit used in the simulation. You can visualize the fit in the material explorer.
  2. Can you share the file (in layout mode) and specify what warning you got?

#3

This post contains additional information on how the wavelength range can affect the simulation: