The curvature of this energy density form creates a "virtual lens". By considering the mass~energy relationship, the "matter wave density" will be in an inverse form. The "matter waves" (or the advanced wave) will be the most dense at the slit edge, and the least in the center of the slit.
One is "energy-wave density", which would be our groundhog, in "photons' clothing"; the other is "matter-wave density" which
could be real, or we could just say that this form takes the opposite/inverse symmetry.
It is simply a container, and the "air" that it contains. (analogy) The air takes the form that the box allows. We are "quite sure" that the box is made of straight lines, but we KNOW that this is not true when we "crank up" the magnification. It would look much more like a sponge network of cavities.
Now, that analogy does not explain the whole picture, but I think you can see the point better with that picture in mind?
At this point, I will have to offer something "new", and "untested", AFAIK. That is why I saved it for last. It should not deter in understanding the basic phenomenon that I have described above.
Before, I do, let me also re-state why I don't think that the "interference" is happening at the slits, and that the slits just "set the stage" for that effect "on the way" to the screen.
The surface polaritons that you mention are in the lattice of the slit material, and move at MUCH slower velocities than light. I stated before that I don't think that there is reaction time (zone) for those waves to effect our passing light wave.
There is also the matter of coupling energies (frequency) being too far from each other to have "strong coupling" (fast).
Last, the polaritons behave (or not exist at all) differently in different materials. Just when we had made the painstaking calculations for the material in our experiment, we would have to start over for each different material. Atomically, all of the elements are different, having different energy, mass, absorption/emission, etc. and would couple differently (or not at all) to certain frequencies.
So, this "other" point (that was caught by both of you) is I left off a bit of the "geometry".
Two slits would, as LL pointed out, restore the "phase question" of C2, and also create the following (poor ASCII art):
...l..l...
...\./...
.........
.../.\...
...l..l...
...l..l...
...\./...
.........
.../.\...
...l..l...
[the ".." represent nothing, they are just for spacing of characters]
The "tooth" that I am always referring to, takes the FORM of a biconvex lens. The slits always (even in 3D, or aperture) take the form of biconcave lens.
We might think of the tooth being a lens for
dark energy; alternatively, for the phase nodes (zero amplitude). (*there is something measurable there)
We also could think of the "dual" affects of the density forms that I mentioned, and LL questioned.
The energy-wave density-form, being convex for the reasons I gave, would converge the anti-node elements of the wave. At the same time (and slit), the "matter-wave density form", being concave for the reasons I gave, would diverge the node elements.
Because of the distance to slit parameter, these 2 causes could combine, and help understand why we have the different phenomenon of 1. The Talbot length "revivals", 2. The near field Fresnel model, and 3. The far field Fraunhoffer model. This is in addition to basic lens characteristics like focal length, the Abbe number (another place where the line is blurred between "human perception", and theoretical Physics). The Abbe number makes (inadvertent) use of the triad, and the working of the eye to set these parameters:
http://en.wikipedia.org/wiki/Abbe_numberQUOTE
nD, nF and nC are the refractive indices of the material at the wavelengths of the Fraunhofer D-, F- and C- spectral lines (589.2 nm, 486.1 nm and 656.3 nm respectively).
[note: colors are yellow, cyan, and orange, respectively]
in this equation

I am trying to make use of virtual positive and negative lenses, to spread our positive and negative phased wave. The intensity does not matter; it is always focused to the center of the pattern. The intensity parameter is shaped by the energy-wave density-form (well known self-focusing). The bands of light and dark however, are all about "phases". Compare the 2 photos, and imagine a specific distance range, and the combined affect of the 2 phenomena that I am proposing:


Here is a link to a very good article on Talbot.
Quantum CarpetsMichael Berry, Irene Marzoli and Wolfgang Schleich (June, 01)
This is very important, because it "carries through" the other 2 models (Fres/Fraun), even though they are not "complimentary" to each other (in their limits). It also measures the "russian doll ~ harmonics" at
fractional revival lengths.
"On the way" is full of surprises!
regards,
T.Roc