I thought that this restricts one to a narrowband source:
(set! kx (* fcen (sin (deg->rad theta))))
(change-k-point! (vector3 kx 0 0))
(change-sources! (list
(make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Hz) (center 0 (+ top dpml)) (size sx 0)
(amp-func (lambda (p) (exp (* 0+2i pi kx (vector3-x
p))))))))
To wit,
http://ab-initio.mit.edu/pipermail/meep-discuss/2007-February/000700.html:
Third, because the magnitude of k depends on the frequency, you can't
make a single source that produces light with a single angle (other
than normal incidence) over a broad bandwidth, as your control file
attempts to do. You need to use a narrow-bandwidth source, and do
multiple simulations if you want a transmission spectrum at a given
angle.
I'd like to do what you describe; create a 2d dataset of scattering
properties over frequency and angle.
Best,
Matt
On Wed, 28 Mar 2007, Steven G. Johnson wrote:
On Wed, 28 Mar 2007, matt wrote:
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.
No, that's not true. A small-df Gaussian is still a Gaussian. It still goes
to zero at both the beginning and end of the simulation, unlike a CW source.
Note that, however, you would want to use stop-when-decayed to wait until the
fields die away, rather than running for a fixed time.
Moreover, a Gaussian is in some sense the optimal shape if you want to
maximize localization in both frequency and time.
However, it's still better to use a short pulse, as described below.
The reason you'd want this is to be able to calculate the scattering
properties for a particular angle of incidence.
Your reasoning is incorrect here.
Assuming you have linear materials, you should get the same results if you
put in a narrow-band Gaussian and look at only one frequency component of the
Fourier transform, or put in a broad-band Gaussian and look at only one
frequency component of the Fourier transform. The latter has the advantage
that it requires a shorter simulation for the fields to die away.
Morever, if you want the scattering properties as function of both frequency
and angle, then the short pulses have a further advantage. Each simulation
with a short pulse and fixed k gives you a broad spectrum result, each
frequency of which corresponds to a different angle. Then you repeat the
simulation for a range of k's, and at the end you'll have a 2d dataset of
transmission/reflection vs. both frequency and angle.
Steven
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