> Can anyone tell me, why the 'measured' spectra seems to be shifted in
frequency?
I take it that is because the emitted flux depends not only on the
spectrum of the dipole source, but also on frequency.
For a planar source (or in 1d simulation) this is not so, there is no
frequency dependence. But for a point dipole in 3d or a line dipole in
2d the situation is more complicated. Look up 'dipole radiation' in
wikipedia, and you will get the idea.
Best,
Mischa
[email protected] wrote:
Dear Meep users:
I set up a simple 2D simulation with a Gaussian source (frequency=2,
fwidth=2) for reference purposes. The whole cell consist of one
material with refractive index n=1.5. Around the source in the center
I've built two 'boxes' as sets of flux-regions (four 1D lines each) to
calculate the flux spectra via add-flux (see attached sketch). The
simulation runs until Ez reaches a certain limit of its peak value.
From the results I sum up the four fluxes for the inner and the outer
'box', respectively. When I check the resulting flux spectra, I
observe a Gaussian-like shaped flux distribution (see attached pic).
Both inner and outer box yield the same spectrum -> the orange line in
the plot. However, the peak frequency is shifted to higher frequencies
w.r.t. to the center frequency of 2. The dashed line shows the
theoretical spectrum of the source (Fourier transform of the the
Gaussian pulse according to the Meep reference), normalized in a way
that both curves have the same integral.
Can anyone tell me, why the 'measured' spectra seems to be shifted in
frequency?
Thanks in advance,
Johannes
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