I am quite confuse about how to assess the confinement of a SPP wave? Based on the literature have been reported, a short wavelength can achieve a good confinement but at the sacrifice of propagation length. For example, Ag can achieve a good modes confinement at 400nm, however the propagation length is only nano-meter scale at that wavelength. On the contrary, the propagation length can achieve tens of micron at 800nm, however the confinement is poor. Can anyone give me some suggestions about why a short wavelength can confine the SPP mode better than a large wavelength? Thanks a lot.
Chuan, it is always the trade-off between the mode localization and propagation length. Roughly speaking, if a (plasmonic) mode is weakly localized, it carries large energy flux and, therefore, it decays slowly. In contrast if the mode is tightly localized near the metal surface, then the Poynting vector is small leading to faster dissipation of energy. In other words, a localized SPP mode expenses its energy at a faster rate.
Also, there is an interesting paper by J Khurgin about fundamental limit to SPP confinement imposed by Landau damping:
http://pubs.rsc.org/en/content/articlelanding/fd/2015/c4fd00193a#!divAbstract
Hi Denis, yes, you are totally right, thanks for your answer and very interesting paper. I also want to ask is the confinement of a SPP wave varying with the wavelength? In J. A. Dionne's paper
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.72.075405
A shorter wavelength can confine the SPP wave better than a larger wavelength, do you have any idea why it is the case? Thanks a lot.
Hi Prof. Khurgin, thanks for you answer, but I cannot read them, maybe they are Russian. By the way, I've read lots of your publications on dealing with the loss in plasmonic waveguides and metamaterials, they are really good wrok. Losses in the plasmonic waveguides are the biggest issue I need to concern in my PhD project.
Yes, it was in Russian...all I did I expressed my pleasant surprise that "Faraday Transactions" paper had been read!
Chuan, what do you specifically mean by "better confinement"? Is it simply a smaller transverse width of an SPP mode at 400 nm, or smaller width normalized by free space wavelength?
Basically, Ag has another permittivity at 400 nm than at 800 nm, so it is no wonder that SPP mode has different field distribution and thus different propagation length and confinement.
Hello Denis, the "better confinement" I meant a smaller transverse width of an SPP mode. Yes, Ag has a smaller negative permittivity at 400 nm than at 800 nm., I think that's the case, thanks a lot.
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