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SURFACE PLASMON POLARITONS

SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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Page 1: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

SURFACE PLASMON POLARITONS

Page 2: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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 plasmonsmanipulate the original light wave properties

plasmons photons

Page 3: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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

Page 4: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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.

Page 5: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

For TM

For TE

Look for propagating wave solutions confined to the interface, with evanescent decay in the perpendicular z-direction.

Page 6: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

look at TM solutions

For z>0 For z< 0

For continuity of Hy and Ez at the interface

A1 = A2

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

Page 7: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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.

Page 8: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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

Page 9: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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.

Page 10: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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

Page 11: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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

Page 12: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

Sensitivity of SPR sensors: The shift per refractive index unit (RIU)

Kall et al. Nanoletters 2005

Page 13: SURFACE PLASMON POLARITONS. SPPs Pioneering work of Ritchie (1957) Propagate along the surface of a conductor Trapped on the surface because of their

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.