Concentration of evanescent/surface waves

[Karthiksrao]

Hello,

At the interface between dielectrics and vacuum, there is always evanescent waves present (you can consider them as being generated due to total internal reflection of electromagnetic waves being generated by thermal fluctuation of charges inside the dielectric). In some cases you can have surface waves like surface polaritons as well, which greatly enhances thermal energy transfer when you bring two dielectric surfaces closely apart (due to coupling of these waves)


I was wondering, if there is any way to concentrate these waves to a tiny spot.. Can we use lenses, the way we use to concentrate any other light wave ?


Thanks!

 

[Bobbywhy]

“Surface Phonon Polaritons Mediated Energy Transfer between Nanoscale Gaps”
Sheng Shen †, Arvind Narayanaswamy *‡ and Gang Chen *†
Nano Lett., 2009, 9 (8), pp 2909–2913

Abstract
"Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such surface waves can lead to breakdown of the Planck’s blackbody radiation law in the near field. Here, we experimentally demonstrate that surface phonon polaritons dramatically enhance energy transfer between two surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies."

http://pubs.acs.org/doi/abs/10.1021/nl901208v

Also, see this Wiki page:
"The Plasmonic Lens is intended to manipulate and focus stimulated surface plasmon polaritons (SPP), resulting in a focus beyond the limitations of conventional lenses."

Note the four references to papers, "Surface plasmon subwavelength optics”, "Focusing Surface Plasmons with a Plasmonic Lens", "Plasmonic Lenses", and "Plasmonic lens in the near field for high-speed nanolithography”.

http://en.wikipedia.org/wiki/Plasmonic_lens

 

[Karthiksrao]

Thanks for the reply. On a related note, I am aware that the momentum of surface polaritons are higher than that of incident light from vacuum and hence cannot be excited by just impinging light on a surface of a metal/dielectric.

In the paper you described above (SPP mediated energy transfer between nanoscale gaps), how are these SPPs activated ? Is it the evanescent waves from one object activating the SPP on the surface of the adjacent object or is it something else that I'm missing ? If it is indeed so, then the momentum of evanescent wave is limited by (\omega*n/c) where 'n' is the refractive index. So why is it that as the gap becomes smaller and smaller, higher modes (with higher momentum) start contributing more and more to the energy transfer?