Frontiers of Engineering Reports on Leading-Edge Engineering from the 2009 Symposium (2010) / Chapter Skim
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Optical Antennas: A New Technology That Can Enhance Light-Matter Interactions--Lukas Novotny
Optical Antennas: A New Technology That Can Enhance Light-Matter Interactions--Lukas Novotny
Pages 45-56
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From page 45... ...
In contrast, radio wave and microwave technology predominantly uses antennas to manipulate electromagnetic fields, controlling them on the subwavelength scale and interfacing efficiently between propagating radiation and localized fields. Recent research in nano-optics and plasmonics has generated considerable interest in optical antennas, and several current studies are exploring ways of translating established radio wave and microwave antenna theories into the opti cal frequency regime.
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From page 46... ...
Analogous to its radio wave and microwave counterparts, we define an optical antenna as a device designed to efficiently convert free propagating optical radiation to localized energy, and vice versa (Bharadwaj et al., 2009)
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From page 47... ...
Most of these differences arise because metals are not perfect conductors at optical frequencies, but are strongly correlated plasmas described as a free electron gas. Optical antennas are also not typically powered by galvanic transmission lines; instead, localized oscillators are brought close to the feed point of the antennas, and electronic oscillations are driven capacitively (Pohl, 2000)
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From page 48... ...
Figure 2a shows the experimentally recorded photon emission rate of a single dye molecule as a function of its separation from an 80nm silver nanoparticle. The superimposed curve is a theoretical calculation based on a simple electromagnetic model in which the molecule is treated as a classical oscillating dipole (Bharadwaj and Novotny, 2007)
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From page 49... ...
(b) Fluorescence rate image recorded by raster scanning of a sample with dispersed dye molecules in a plane z ≈ 5nm underneath a nanoparticle antenna.
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From page 50... ...
For a near-field optical image, the optical antenna is guided over the sample surface in close proxim ity, and an optical response (e.g., scattering, fluorescence, antenna detuning) is detected for each image pixel.
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From page 51... ...
The notion of an effective wavelength can be used to extend familiar design ideas and rules into the optical frequency regime. For example, the optical analog of the λ/2 dipole antenna becomes a thin metal rod of length λeff/2.
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From page 52... ...
Near an optical antenna, the photon momentum is no longer defined by its free space value. Instead, localized optical fields are associated with a photon momentum defined by the spatial confinement, D, which can be as small as 1 to 10nm.
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From page 53... ...
This is the case in semiconductor nanostructures, for example, where the low effective mass gives rise to quantum orbitals with large spatial extent. CONCLUSIONS AND OUTLOOk Research in the field of optical antennas is currently driven by the need for high field enhancement, strong field localization, and large absorption cross sec tions.
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From page 54... ...
2007a. Effective wavelength scaling for optical antennas.
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From page 55... ...
2007. Surface plasmon enhanced silicon solar cells.
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