Thanks for the reply.
My trouble with this is that it isn't compatible with the periodic plane
wave excitation:
I can create a planewave with oblique incidence and periodic boundaries,
but only if the source is very narrowband (df is small). A large df
doesn't work because the periodic boundaries are frequency specific.
For a gaussian source, a small df practically makes it a continuous
source, producing the same results.
The reason you'd want this is to be able to calculate the scattering
properties for a particular angle of incidence.
Kind Regards,
Matt
On Tue, 27 Mar 2007, Steven G. Johnson wrote:
On Tue, 27 Mar 2007, matt wrote:
My simple meep example is coming up with an incorrect result.
I found some posts on the list regarding similar problems (incorrect
reflection coefficient calculation), where the recommendation was to move
the flux planes away from the source, by at least a wavelength. This did
not solve the problem for me.
In my example, I have a 2D simulation, with periodicity in X, and PML in
Y. The scatterer is a dielectric slab with epsilon 9. The source is a
plane wave source at the upper PML interface (the angle of incidence is 30
degrees).
code:
http://www.pastebin.us/19072
This code is using a continuous-src, which is not appropriate. You need to
use a gaussian-src for a flux-spectrum calculation. More generally, you need
to use some current source that goes to zero as t -> infinity.
Think about how Meep computes a flux spectrum, as described in the manual
(see e.g. the introduction section). It computes the Fourier transform of
the fields in the flux plane, and then computes the flux of the
Fourier-transformed fields. This doesn't make (much) sense for a
continuous-src, because the fields are not integrable---their Fourier
transform will not converge as you run for longer and longer, because the
source doesn't stop. So, you end up chopping off the fields at some point
arbitrarily. But this "windowing" does different things to the normalization
and computation runs, because the spectra are different in the two cases. In
contrast, if you use a Gaussian source, then the fields are L2-integrable and
everything is well-defined and convergent if you run for long enough to let
the fields decay away.
Steven
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