Source of SiO2 Dielectric Function

[BradenCzapla]

Hi Homer,

You provided a Julia code on your documentation page concerning heat transfer between two SiO2 spheres. In that code you wrote a function which calculates the dielectric function, which I've copied below. Can you tell me the source of those parameters? I've been unable to find them in the literature.

Thank you!

`function EpsSIO2_Krueger(u)

w=3.0e14*u; A1 = 8.2736e+13; w01 = 8.54484e+13; G1 = 8.46448e+12; A2 = 1.58004e+14; w02 = 2.029e+14; G2 = 1.06449e+13; A3 = 3.39786e+13; w03 = 1.51198e+14; G3 = 8.33205e+12; EpsInf = 2.03843;

EpsInf + A1A1/(w01w01 - ww - imwG1) + A2A2/(w02w02 - ww - imwG2) + A3A3/(w03w03 - ww - imw*G3); end`

[HomerReid]

I got these parameters from Matthias Kruger, who (I believe) got them from the Handbook of the Optical Constants of Solids.

Feel free to ask more questions, or close the issue if satisfied.

[BradenCzapla]

Hi Homer,

Thanks for getting back to me. I had checked Palik's handbook but it seems the optical properties do not quite line up. I'm attaching a comparison plot below of the real and imaginary components of the refractive index to show you what I mean.

[HomerReid]

Actually, those fits don't look bad at all to me! It's hard to think of any broadband quantity that would be particularly sensitive to the difference between the red and green curves here, and certainly in a Casimir or heat-transfer calculation any discrepancy should be negligible. Of course, if you are doing something narrowband at a very specific frequency then you might want to use a different fitting function that is optimized for that particular frequency, but for broadband physics I would say your plots confirm the usefulness of the parameterization.

[BradenCzapla]

I don't disagree that the fit is representative of silica. Truthfully, I'm hoping to use the function in my work but need to cite a peer-reviewed source for the parameters.