SPP at plane interfaces, dispersion curve. confused by textbook?

[iLIKEstuff]

the link below should take you to a google book called "principles of nano-optics" by novotny and hecht. my question is on the dispersion curve plot they have on page 388/389 figure 12.5 and 12.6. it is describing the surface plasmon polaritons. the part i don't get is this excerpt which can be found on page 389 about half way down...

"However, as the disperion curve approaches this line the losses start to increase drastically. As a consequence, as \omega is further increased the dispersion curve bends back and connects to the upper branch." (you'll have to look at page 388 fig 12.5 to see both branches they're talkin about)

the bolded part is the part i don't get. what does "bend back" mean? how is it connecting to the upper brancH? the two lines are separated throughout the whole kspace? can someone explain to me what this is and also where the "connecting region" they mention can be found on the plot?

also, at the bottom of pg 389, it says
"the physical reason for the increased momentum of the SPP is the strong coupling between light and surface charges. the light field has to drag the electrons along the metal surface"
i don't get this either. wouldn't dragging the electron cause it to lose speed? and therefore momentum? i know that momentum here is p = \hbar k but it seems that dragging would cause it to lose momentum. and what does the first sentence mean? what is exactly the meaning/usage of the word coupling in this context? how does coupling allow it to have more momentum?http://books.google.com/books?id=Qr...&hl=en&sa=X&oi=book_result&resnum=1&ct=result

thanks guys.

 

[BiBByLin]

I think the \varpi coordinate should be normalized, if you want to have a good comprehension. When \varpi increase, it can not obey the SPPs but the free gas plasmons dispersion in upper band.

 

[BiBByLin]

secondly, I do not think dragging is a good term. If you use resonance, you could have a good comprehension. (In my opinion)