With finite-difference time-domain (FDTD) simulation, it is possible to calculate both scattering and absorption cross-section of metal nanoparticles using total-field scattered-field (TFSF) source method.
In our work, we introduced Ag nanoparticle in an absorbing medium and it is essential to compare its scattering and absorption cross-section.
If the Ag NP is situated in non-absorbing media, we can easily calculate absorption cross-section of Ag NP using TFSF source method, as in the case of Mie 3D example ( lumerical FDTD).
However, when Ag NP is it in the absorbing medium, then the TFSF source method will give absorption cross-section of both Ag NP and absorbing medium together (Ag NP+absorbing medium).
My question is how can we able to calculate absorption cross-section of Ag NP if it is situated in an absorbing medium?
To get more idea about my question, please see the attached figure.
I am not so familiar with the computational method, but assuming that the NPs "dilute" the absorbing media, you may be able to deduce the Ag NP absorption by taking the difference between the absorption of the NPs + absorbing medium and the absorption of the absorbing media with air holes instead of the NPs.
Hi
I think it is the same... easily, you change the medium and compare the results... you should see the difference.
BR
MOhammad
@Mohamed Elkabbash and Mohammad Tavakkoli Yaraki
Thanks for your response.
But, the explanations may not be suitable in the reported question.
Here,
Abs(Ag + absorbing medium) not equal to Abs(Ag) + Abs(absorbing medium)
This is due to the plasmonic effects of Ag NP. The plasmonic effects lead to light absorption enhancement of the absorbing medium through high angled scattering and near-field concentration of incident light.
Thus, the recommended method is not useful to calculate absorption cross-section of Ag NP introduced in an absorbing medium.
Yes Shamjid, you are absolutely correct. I did not consider the absorption enhancement. In fact a similar problem was mentioned in the attached paper, here the absorbing medium is dye surrounding Au NPs. check how he produced figure 5 and the discussion before it. I am not of much help, simulations are not my forte.
Best wishes
Mohamed
Dear Shamjid
pls check the lumerical, before start the simulation you can indicate the medium... it means that the software will solve based on it!
I think a solution to your problem would require you to export the filed profiles form the simulation containing both the Ag nanoparticle and the absorbing medium and introducing them into another simulation containing just the absorbing medium with an air hole at the location of the Ag nanoparticle.
This is a comment to keep the discussion alive ;)
The absorption of the material depends on the travel distance through the medium. Due to the particle the Poytning-vector changes drastically, increasing the path length of many light rays through the material, That should add up to the absorption and without taking the time to test it, it should hold: absorption(medium + particle) > absorption(medium) + absorption(particle).
So it might be tedious, but try to numerically evaluate the pathlength of all light paths in the simulation. Then use the known absorption coefficient of the material to calculate its absorption using the evaluated light path lengths. Substract this from the absorption(medium + particle) and you should have the absorption you search for.
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