Calculating the extinction cross section of a dual-disk ring plasmonic nanostructure

Hello again,

Any idea why do i get oscillations or wriggles at the start of my results?

I have already increased my simulation time and also lowered the auto shutoff time.

extinction cross section.fsp (623.0 KB)

I realized that the wriggles or oscillations became smoother after i changed the refractive index to Palik (0-2um).
However, in the reference, it was mentioned that Johnson & Christy was used.

Is there a way to smoothen the plot in Lumerical FDTD?

Sorry, i am just reproducing a few papers work to familiarize myself with the workings of FDTD because i am learning on my own.

Hi @wxlim1,

Did you try increasing the simulation time? Is the auto-shutoff triggered? Small ripples in the frequency-domain results are usually due to an early termination of the simulation (before the fields in the simulation region have decreased enough).

It is possible that with a different material model, the simulation behaves slightly different and the fields decay faster.

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Yes, the simulation time is 3000 fs and from the log file,

“All processes are communicating and ready to proceed to simulation…
Starting 819878 total iterations

11% complete. Max time remaining: 4 hrs, 26 mins, 56 secs. Auto Shutoff: 2.03411e-006
Early termination of simulation, the autoshutoff criteria are satisfied.”

I supposed it was triggered.

I don’t think the problem is the simulation time. When I checked the file, I added a time monitor and the field actually dies after 800 fs. You are trying to reproduce the results of a paper, aren’t u? Would you show us the spectrum they published?

This is the spectrum. The x-axis is in energy (eV).
Notice that there is no wriggles in their results.

I tested the effect of decreasing the bandwidth of the plane wave source. As in the figure below, the smaller bandwidth results in less wiggles. This is a reproduction of (h)

Focusing the frequency span from 200 THz to 600 THz, mitigates the wiggles effect even more:

Hi @aya_zaki ,

Why does focusing the frequency span reduce the wriggles effect? I have no idea.
It should not affect the optical properties of the metal or plane wave source.

And, does that mean i should break the simulation into 2 parts of wavelength range?

Also, in the paper, they calculated the divergence of the electric field.

Could anyone enlighten me how should the analysis group be placed? It seems that it requires large memory to perform this.


I think you are using the charge and current density analysis group to calculate the divergence of E as described here:

The size of the group could be set to the same as the total analysis group in your file. Since as you mentioned, the memory required by the monitors is large since the monitors are 3D, you probably don’t want to have the size much larger than the resonator structure.

The analysis script used in this analysis group calculates not only the divergence of E, but it also calculates additional results such as current density and charge density. Since each of these results is over the full 3D volume, they can require a lot of memory to calculate. You might want to go through the analysis script and remove the portion of the calculation for the results that you are not interested in. Hopefully this helps!