Giovanni,
It depends on what you are trying to do. If you are simply interested
in an integrated flux quantity e.g. total scattered flux, then all the
tools you need are already built into meep, as you quote from the
tutorial. Strictly speaking, this is sufficient to calculate
scattering and absorption cross sections. In fact, I haven't actually
tried to cook up scheme code to do this directly for an example
geometry, but it shouldn't be too difficult!
On the other hand, if you're interested in looking at spatially-
resolved spectra (e.g. electric field as a function of (omega, x, y,
z)) you'll have to (to my knowledge) crank these out the way I
described, by manually loading and manipulating data saved in a
collection of H5 files. While this "manual" method is less
straightforward, it allows maximum flexibility in data analysis. One
of the coolest applications of this method is computing radiation
patterns using the scattered field spectra.
Good luck,
Alex
On Dec 23, 2010, at 9:00 AM, [email protected]
wrote:
From: gpipc <[email protected]>
Date: December 23, 2010 7:48:21 AM PST
To: <[email protected]>
Cc: Alex McLeod <[email protected]>
Subject: Re: [Meep-discuss] Regarding Near field enhancement and
Scattering cross section
On Thu, 23 Sep 2010 18:38:22 -0700, Alex McLeod
<[email protected]>
wrote:
Hi Jack,
In regards to your questions about near-field enhancement and
scattering, I have some comments to make.
(cut)
Also, note that using flux regions will only let you compute
absorption, since fluxes won't let you spatially resolve the radiated
fields. The formula "E_scat=E_total-E_incident" is the conventional
way of "defining" the "scattered" part of the field distribution.
Since Maxwell's eqtns are linear, you know E_scat is induced only by
the charges in your geometry rather than by the source currents. But
to obtain this, you have to apply that formula using the spatially-
resolved field distributions in each of the incident faces to get
E_scat, etc. So, you need to output the in-plane fields in those
regions to HDF5 so you can load the data and do this calculation with
the spatially resolved fields. Then, calculate and integrate the
resulting Poynting vector fluxes. This is a NONTRIVIAL exercise, and
you will have to do some scripting to pull it off. I have written an
API to accomplish this, which I'll be publishing as part of an
interface to Meep at www.nanohub.org under the title "Molecular
Foundry Nanophotonics Toolkit" (crediting S. Johnson et al.), so keep
an eye out for that in the coming months.
Dear Alex and Meep users,
I have just read today this mailing list message posted last
September and
I have a question. Isn't the procedure you describe accomplished by
using
the save-flux and load-minus-flux commands (for each of the surfaces
of the
box which includes the scattering object) in the libcl interface to
Meep?
Let me quote from the Meep tutorial webpage
"Now, as described in the Meep introduction, computing reflection
spectra
is a bit tricky because we need to separate the incident and reflected
fields. We do this in Meep by saving the Fourier-transformed fields
from
the normalization run (no-bend?=true), and loading them, negated,
before
the other runs. The latter subtracts the Fourier-transformed incident
fields from the Fourier transforms of the scattered fields;
logically, we
might subtract these after the run, but it turns out to be more
convenient
to subtract the incident fields first and then accumulate the Fourier
transform. All of this is accomplished with two commands, save-flux
(after
the normalization run) and load-minus-flux (before the other runs). "
What is the difference with the procedure you describe? Thanks in
advance
for the answer,
Giovanni
--
================================================
Giovanni Piredda
Postdoc - AK Hartschuh
Phone: ++49 - (0) 89/2180-77601
Fax.: ++49 – (0) 89/2180-77188
Room: E2.062
----------------------------------------
Message sent by Cup Webmail (Roundcube)
_______________________________________________
meep-discuss mailing list
[email protected]
http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
