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SURFACE PLASMON POLARITONS
SPPs
• Pioneering work of Ritchie (1957)
• Propagate along the surface of a conductor
• Trapped on the surface because of their interaction with the
free e• photons
plasmons
manipulate the original light wave properties
plasmons
photons
SPs have a combined
electromagnetic wave and surface
charge character
Evanescent field reflects non-radiative nature
of SPs, prevents power from propagating away
from the surface
For propagation along the x-direction and homogeneity in the y direction
This system allows two sets of self-consistent solutions with
different polarization properties of the propagating waves.
For TM
For TE
Look for propagating wave solutions confined to the interface, with
evanescent decay in the perpendicular z-direction.
look at TM solutions
For z>0
For z< 0
For continuity of Hy and Ez at the interface
A1 = A 2
Confinement to the surface demands Re [ε1] < 0 if ε2 > 0
The surface waves exist only at interfaces between materials with opposite signs of the
real part of their dielectric permittivities
Expression for Hy has to fulfill the wave equation
Interaction between the surface
charge density and the
electromagnetic field results in
the momentum of the SP mode
being greater than that of a
free-space photon of the same
frequency.
Three main techniques:
1. Prism coupling to
enhance the
momentum of the
incident light
2. Scattering from a
topological defect on
the surface, such as
a subwavelength
hole
3. Use of a periodic
corrugation in the
metal’s surface
The propagation length sets the upper size limit for any
photonic circuit based on SPs
The decay length in the dielectric material dictates
the maximum height of any individual features
The decay length in the metal determines the minimum feature size
that can be used thus highlighting the need for
good control of fabrication at the nanometer scale.
Surface plasmon band structure and
periodic surfaces
PBG: Using wavelength-scale periodic structures to manipulate the
interaction between light and matter
Periodically structured insulating and semiconducting materials
Making use of SPs,
metals too can be used as PBG materials
a, equal to half the wavelength of the SP
Two SP standing wave solutions
Within a bandgap,
the density of SP modes is zero
At the band edges,
dispersion is flat and the associated
density of SP modes is high
Kall et al. Nanoletters 2005
Sensitivity of SPR sensors:
The shift per refractive index unit (RIU)
References
•
Plasmonics: Fundamentals and Applications, by Stefan Maier
•
Nature insight review articles: Surface Plasmon subwavelength optics, by Barnes et
al.
•
Applied Physics Reviews- Focused Review: Plasmonics: Localization and guiding of
electromagnetic energy in metal/ dielectric structures, Maier et al.
•
Nano Letters: Plasmonic Sensing Characteristics of Single Nanometric Holes, by Kall
et al.
•
IEEE Journal of Selected Topics in Quantum Electronics: Plasmonics: Metal
Nanostructures for Subwavelength Photonic Devices, by Stefan A. Maier
•
Sensors and Actuators B: Surface plasmon resonance sensors: review, Homola et al.