the changing damping factor of material



hi, i simulated the effect of the damping factor of Al on the transmission spectra, however i didnot get a shift of resonance peaks, which does not make sense in physics.however, i do get a narrow resonance with decreasing damping factor. Is it because of the fitness of the material? the refractive index was obtained by changing the damping in the Drude-Lorentz model.

refractiveindex-0.1gamaD.txt (29.3 KB)
refractiveindex-2gamaD.txt (29.3 KB)
refractiveindex-gamaD.txt (29.3 KB)
ND100-0.1gamaD.fsp (363.1 KB)
ND100-2gamaD.fsp (347.0 KB)
ND100-gamaD.fsp (331.0 KB)


Dear @feng.tang

Sorry for my late reply. Material fitting seems reasonable to me. However, I am not quite sure what do you expect from the simulations and specifically what you mean by shift in resonance. My understanding is that transmission varies as you change the material (Al here) but the resonance is too wide that you probably won’t capture any shift as Al material behaves more or less similar. More clarification would definitely be useful.



Thanks for the reply.In my opinion, since the energy loss increase with the damping factor, the valley in the spectra should move to the longer wavelength. You said “More clarification would definitely be useful.”, could you give me a clue please? I totally have no idea.


Dear @feng.tang

My understanding is that since the maximum of damping factor occurs in the same wavelength for all these three materials, there shouldn’t be a shift in the valley. Can you please provide an evidence, such as a paper or physical effect, that explains why you should see a shift?



hi, sorry for this late reply. I have been thinking how to better reply your question. I think the meaning of damping in the Drude model decides there will be a shift when it changes. personally speaking, it is kind of like the bigger nanodisk will have longer wavelength peak of resonance than the smaller nanodisk. here is a experimental result for your consideration.
Encapsulated Annealing: Enhancing the Plasmon Quality Factor in Lithographically–Defined Nanostructures


dear@bkhanaliloo, do you think the distance of the source and monitor with the metal structure, the distance between the monitor and the source with the PML are suitable?


Dear @feng.tang

The way that you set up your simulation, it looks like you are having periodic structures. If this is not what you want to simulate, we need to adjust the boundary condition (such as x-min: Antisymmetric, x-max:PML and y-min: symmetric, y-max=PML), and then use a TFST source to avoid edge effects.

If you want to test and make sure that you have set your simulation properly, my advice would be to change the the FDTD simulation region, mesh size, as well as the monitor position and make sure that your results remain stable.


Dear @feng.tang

I modified the simulations (using TFSF and PML boundary conditions) and run the simulations for three different material that we have. Here is the simulation file: ND100-Gamma.fsp (366.8 KB)

Below is the transmission plot for different materials. While there are some shifts in the spectrum, but it is hard for me to understand them.

The best approach for you would be to replicate simple results of a paper. This will be quite useful for troubleshooting. Unfortunately, I am not still clear of what we are looking and the geometry/physics that we want to study.


dear@bkhanaliloo, my structure is periodic. But in the new file you give to me, it is isolated structure, right? I notice that the three material have different RMS, does this matter for the shift?


Dear @feng.tang

Yes, my simulation file is set for single cell/isolated structure. I thought that you want to do simulation similar to the paper that you sent me. However, if your structure is periodic your original file has the proper settings.

The RMS error value in the material fitting is the result of fit to experimental data. In the simulation, software will use the fit data. While these fits are reasonably OK, for the purpose of your work you might try to improve them.