Absorption cross-section of Ag nanoparticle situated in an absorbing medium

We know with total-field scattered-field (TFSF) source method both scattering and absorption cross-section of metal nanoparticles can be able to calculate.

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.

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 file.

Hi @sivaji,

There are basically two approaches available for absorption calculations:

  1. Use box monitors surrounding the structure of interest and then use the transmission values from the monitors to calculate the total absorbed power
  2. Calculate the absorbed power as a function of space and integrate it over the region of interest.

The Pabs analysis group for the Mie example takes the first approach and would not be suitable when multiple materials and/or structures are involved as in your case. In those situations, you will need to take the second approach, which involves integration of local absorption over the desired space. To calculate the absorption by the Ag nanoparticle only, you need an integration filter that can separate it from the surrounding material. Here again, you have two options available - spatial filter and index filter.
You can mathematically define the spatial region corresponding to the Ag particle, or if the background material has a different index from the Ag, then you can use a filter based on the index difference. Please have a look at the following pages for further information about calculating absorption in a filtered region.

https://kb.lumerical.com/en/index.html?layout_analysis_pabs_simple.html (See ‘Absorbed power in spherical region’ section)
FDE Solver - Modal Analysis - Power Integration over a Triangle

Thank you so much for your valuable and detailed explanations !

I will try to modify the simulation based on your suggestion.

Thanking you.