On Wed, 8 Nov 2006, Loïc Le Guyader wrote:
In order to have frequency-dependent permittivity in meep, we have to
decompose it in a sum of Lorentzian.
But it's not always possible. One material I want to use is transparent in a
certain region and I can't fit it with Lorentzian because there feet doesn't
disapears in this region.
Enough Lorentzians should form a complete basis, so you should be able to
fit any function given enough Lorentzians.
(I suspect that harminv's algorithm could be adapted to the purpose of
finding the best fit, but I've never tried this. Probably some work would
be required since right now harminv is oriented only towards finding the
well-defined resonances rather than to fitting the whole spectrum. You
can refer to the papers by Mandelshtam on the harminv web site if you want
to play with this yourself.)
I guess gaussian would work, at least it has been reported in litterature. Is
it possible to have gaussian sum supported in meep ?
Currently it doesn't support anything other than Lorentzians.
I haven't heard of a way to implement Gaussian material dispersion in
time-domain, do you have a reference? Normally, material dispersion is
implemented in the time-domain by integrating auxiliary differential
equations, and a linear differential equation can only implement a
rational polynomial frequency response.
Steven
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