Dear all,
I am trying to simulate scattering/ extinction spectra of a silicon torus on a substrate (n = 1.5, k = 0). The thickness of substrate is 250 nm. I try to observe extinction, scattering and absorption cross-sections for visible wavelength range (550 nm - 800 nm). We have done multi-polar analysis following the approach depicted in [1].
For 130 nm major radius, I got extinction cross-section (normalized by lambda^{2}/2*pi) more than 200, which is great amount of deviation from the theoretical values.
I am modelling my simulation as per the COMSOL standard model "scatterer_on _substrate.mph" [2].
I will be really thankful if you could help me to find out reason of these anomalous results.
[1] R. Alaee, C. Rockstuhl, and I. Fernandez-Corbaton, "An electromagnetic multipole expansion beyond the long-wavelength approximation," Opt. Commun. 407, 17–21 (2018).
[2] https://www.comsol.com/model/scatterer-on-substrate-14699
I think that k = 0 is not possible for your substrate system (I assume soda-lime glass or similar). Try a non-zero component such as 0.001 and note the effect. Have you the correct optical properties for the silicon at the wavelengths you use?
Dear Alan, I have collected the complex refractive index of Si from [1,2]. I have put zero values for k of substrate as I have assumed no loss is occurring in the substrate in the visible region. Does loss occur in glass/ SiO2 substrate in visible spectrum?
[1] D. E. Aspnes and A. A. Studna. Dielectric functions and optical parameters of Si, Ge, GaP, GaAs, GaSb, InP, InAs, and InSb from 1.5 to 6.0 eV, Phys. Rev. B 27, 985-1009 (1983)
[2]https://refractiveindex.info/?shelf=main&book=Si&page=Aspnes
Any interface or optical heterogeneity in a system will incur loss of light - modeled by an increase in k.
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