# Spectrally fluctuating result when calculating absorption cross-section

#1

Hello, Im chunho @ south korea.
I have encountered strange result that I cannot find a reason by myself.

Im calculating a absorption cross-section of Al nanosphere( radius 32nm) in ultraviolet spectrum.
I used TFSF source and default analysis library ‘cross-section’

Resulting scattering cross-section(Sca.) matches well with the Mie calculation, but
Absorption cross-section (Abs.) does not.
The Abs. has about twice larger value than Mie calculation and spectrally fluctuation.

At the very same condition, if I switch the material to dielectric nanosphere with (n.k.)=(3,1).
I got a good result with both of the Abs. and Sca.
Fitting of aluminum using material explorer was good.

Can anyone have an idea of what the problem is?

Below, I attach the link of my fsp files.
It took only a few minutes of time to calculate it.

#2

Hi @lch5717

Original Mie scattering example uses gold for the particle. When you change the material to aluminium which has different refractive index, you expect to see a change in the absorption. Can you please further clarify which part does not make sense?

Thanks