Ziming Meng <mengzm_m...@yahoo.cn> wrote:
> ???????? I want to output the backwardly reflected field
> pattern for normal incidence. However, it is usually superimposed
> with the backward propagation of the light source. Then just using
> the output-field function fails to do that. In calculating reflection
> spectrum? there is a tricky way to separate incident and the
> reflected field as is indicated in the tutorial. So how can I just
> output the backwardly reflected field pattern subtracted from the
> background of the light source? Can anyone give me an example?
Make a uni-directional light source. This is easy if it is located
in a dispersionless medium. If you want it propagating along the
z-axis in a vacuum, create two sources that are identical except
that one is (component Ex) and the other (component Hy).
Changing the sign of one amplitude wrt the other reverses the direction.
Using a fixed refractive index means that Hy (or Ex) will need to
change size. You want:
sqrt(epsilon) Ex \pm sqrt(mu) Hy = 0
... with sign depending on direction.
If you to embed a directional source in a dispersive medium you
will have to live with it being approximate; likewise if you want
to specify a direction the isn't along a lattice direction I think
(I haven't tried it yet) you'll get small, resolution dependent,
and remarkably persistent imperfections.
More generally (but for spatially propagated, not time-propagated FDTD), see
Phys. Rev. A72, 063807 (2005) doi:10.1103/PhysRevA.72.063807
or the newer
Phys. Rev. A81, 023808 (2010) doi:10.1103/PhysRevA.81.023808
--
---------------------------------+---------------------------------
Dr. Paul Kinsler
Blackett Laboratory (Photonics) (ph) +44-20-759-47734 (fax) 47714
Imperial College London, dr.paul.kins...@physics.org
SW7 2AZ, United Kingdom. http://www.qols.ph.ic.ac.uk/~kinsle/
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