Tutorial: Scattering by a metallic sphere

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This tutorial is an extension of the prior scattering by a dielectric sphere tutorial. In it, the prior tutorial will be repeated, but for a silver particle. As discussed in the prior tutorial, looking forward to later tutorials, the solution will be purposefully not converged.

You will learn:

Note again that the geometries file will not be created for this problem[1]. The files for this tutorial (input and expected output) can be obtained here: Tutorial2.tgz

Note also that this tutorial assumes that you are thoroughly familiar with the scattering by a dielectric sphere tutorial.

Preparing the work directory

Create a work directory, work/. Copy the input files from the scattering by a dielectric sphere tutorial, param, mat, and geom.unv, to this directory.

Geometries file

The geometries file from the scattering by a dielectric sphere tutorial, geom.unv, will be used in this tutorial.

Materials file

The primary task in this tutorial is to modify the materials file from the scattering by a dielectric sphere tutorial, replacing glass with silver. Recall that the sphere is assigned a material number 1.

Open mat in a text editor, and replace:

material 1
{
    epsr 2.25
}

with the following model for silver:

material 1
{
    epsr 3.189

    Drude
    {
        omegap 9.183
        gamma 0.0179
    }

    Lorentz
    {
        depsr 0.4323
        omegap 4.668
        delta 0.207
    }

    Lorentz
    {
        depsr 0.2237
        omegap 4.240
        delta 0.186
    }
}

Save this file.

Parameters file

The parameters file from the scattering by a dielectric sphere tutorial, param, will be used in this tutorial.

Running FDTD++

Now that the relevant files have been created, the simulation can be performed.

Open a terminal in your work directory, and since this simulation is to be run in serial, type:

FDTDxx param mat geom.unv

Output

Once the simulation has finished, the following output should exist:

  • work/FDTDxx.log
  • work/FDTDxx.err
  • work/output/cross_sections.dat

First, check work/FDTDxx.err to ensure that no errors were generated during the simulation.

Next, check work/FDTDxx.log for any important notes. Also, double check the definition of materials and simulation parameters, as reported.

Finally, work/output/cross_sections.dat contains the cross sections, which can be plotted, etc.

Notes and references

  1. The creation of a 10 nm radius sphere is covered in the tutorial Creating a sphere with SALOME