Radiation Engineering of Optical Antennas for Maximum Field Enhancement

Seok, Tae Joon; Jamshidi, Arash; Kim, Myung‐Ki; Dhuey, Scott; Lakhani, Amit; Choo, Hyuck; Schuck, P. James; Cabrini, Stefano; Schwartzberg, Adam M.; Bokor, Jeffrey; Yablonovitch, Eli; Wu, M.C.

doi:10.1021/nl2010862

Cited by 188 publications

(191 citation statements)

References 27 publications

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“…The regime of high energy storage (II) occurs when the radiative and non− radiative losses exactly compensate each other (γ c = γ i ), which is analogous to the impedance matching condition in the design of antennas. 10 This condition which we will refer to as the critical coupling, corresponds to b = 1/4 and can thus be deduced from the far-field pattern. The quantitative relations between modulation damping and energy storage drawn from this model are valid for any linear wave-propagating system with coupled radiative and nonradiative channels.…”

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confidence: 99%

Plasmonic Radiance: Probing Structure at the Ångström Scale with Visible Light

et al. 2013

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Plasmonic modes with long radiative lifetimes combine strong nanoscale light confinement with a narrow spectral line width carrying the signature of Fano resonances, making them very promising for nanophotonic applications such as sensing, lasing, and switching. Their coupling to incident radiation, also known as radiance, determines their optical properties and optimal use in applications. In this work, we theoretically and experimentally demonstrate that the radiance of a plasmonic mode can be classified into three different regimes. In the weak coupling regime, the line shape exhibits remarkable sensitivity to the dielectric environment. We show that geometrical displacements and deformations at the Ångstrom scale can be detected optically by measuring the radiance. In the intermediate regime, the electromagnetic energy stored in the mode is maximal, with large electric field enhancements that can be exploited in surface enhanced spectroscopy applications. In the strong coupling regime, the interaction can result in hybridized modes with tunable energies. KEYWORDS: Fano resonances, electromagnetically induced transparency, plasmonic nanosensors, surface enhanced Raman scattering (SERS), extraordinary optical transmission W ith their ability to concentrate light at a deepsubwavelength scale by excitation of surface plasmons, metallic nanostructures play a major role in current nanoscience. 1 In particular, optical tweezers, 2 antennas, 3,4 lasers, 5 photodetectors, 6 or biochemical sensing platforms 7,8 have been scaled down to the nanometer range. However, their performance are limited by the short lifetimes of surface plasmon resonances. 9 Recently, it has been shown that the use of plasmonic modes with long radiative life times (subradiant modes) can drastically enhance the performance of nanophotonic devices. 10−12 Their spectral response carry an asymmetric line shape with sharp spectral features, characteristic of Fano resonances. 13−22 The coupling of subradiant modes to radiation, their radiance, is directly controlled by the geometrical configuration of the nanostructures, 19 and also governs their optical response and the location and amplitude of light confinement. 20 Despite the fact that the use of subradiant modes for nanophotonic applications critically depends on the coupling strength, the choice of an optimal regime has so far never been addressed.In this work, we use a universal model for interacting radiative and localized channels to investigate the radiance of a plasmonic mode. We demonstrate that the radiance of a plasmonic mode can be classified into three different regimes. In the weak coupling regime, the radiance of the mode is small and extremely sensitive to perturbations in the coupling. We introduce a novel sensing concept, radiance sensing, which is based on the sensitivity of the radiance to the environment, rather than conventional plasmon sensing relying on the wavelength shift of plasmon modes. 8 In the intermediate regime, the radiative damping is equal to the int...

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confidence: 99%

Plasmonic Radiance: Probing Structure at the Ångström Scale with Visible Light

et al. 2013

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“…It should be noted that this is smaller than the typical quarter wavelength value due to penetration into the metal, as well as impedance matching effects [43].…”

Section: Design and Fabricationmentioning

confidence: 84%

“…Impedance matching and reduction of mode volume of the antenna provide maximum local field enhancement [43]. Figures 5(a) and 5(b) show the local field intensity in the antenna gap for gap sizes of 20 and 5 nm, respectively, at the design wavelength of 840 nm (log scale).…”

Section: Simulation Resultsmentioning

confidence: 99%

“…It has been recently shown that maximum field enhancement results when power radiated by the antenna is equal to the power loss in the antenna [41][42][43]. This is commonly referred to as impedance matching in microwave antenna theory [39].…”

Section: Antenna Design Parametersmentioning

confidence: 99%

“…This is commonly referred to as impedance matching in microwave antenna theory [39]. Even higher local field can be achieved by reducing the mode volume of the antenna by reducing the feed gap between the two elements of the dipole antenna [43]. …”

Section: Antenna Design Parametersmentioning

confidence: 99%

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Antenna Design for Directivity-Enhanced Raman Spectroscopy

Ahmed

Pang

Hajisalem

et al. 2012

International Journal of Optics

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Antenna performance can be described by two fundamental parameters: directivity and radiation efficiency. Here, we demonstrate nanoantenna designs in terms of improved directivity. Performance of the antennas is demonstrated in Raman scattering experiments. The radiated beam is directed out of the plane by using a ground plane reflector for easy integration with commercial microscopes. Parasitic elements and parabolic and waveguide nanoantennas with a ground plane are explored. The nanoantennas were fabricated by a series of electron beam evaporation steps and focused ion beam milling. As we have shown previously, the circular waveguide nanoantenna boosts the measured Raman signal by 5.5x with respect to a dipole antenna over a ground plane; here, we present the design process that led to the development of that circular waveguide nanoantenna. This work also shows that the parabolic nanoantenna produces a further fourfold improvement in the measured Raman signal with respect to a circular waveguide nanoantenna. The present designs are nearly optimal in the sense that almost all the beam power is coupled into the numerical aperture of the microscope. These designs can find applications in microscopy, spectroscopy, light-emitting devices, photovoltaics, single-photon sources, and sensing.

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Life Beyond Diffraction: Opening New Routes to Materials Characterization with Next‐Generation Optical Near‐Field Approaches

Schuck

Weber‐Bargioni

Ashby

et al. 2013

Adv Funct Materials

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Near-fi eld optical microscopies and spectroscopies seek to investigate materials by combining the best aspects of optical characterization and scan-probe microscopy techniques. In principle, this provides access to chemical, morphological, physical and dynamical information at nanometer length scales that is impossible to access by other means. But a number of challenges, particularly on the scan-probe front, have limited the widespread application of near-fi eld investigations. This work describes how recent probe engineering and technique innovation have addressed many of these challenges. This Feature Article begins with a short overview of the fi eld, providing perspective and motivation for these developments and highlighting some key improvements. This is followed by a more in-depth description of the near-fi eld advances developed at the Molecular Foundry, a national nanoscience User Facility-advances that provide groundwork for generally-applicable nano-optical studies. Finally, a discussion is provided of what progress is still needed in order to realize the ultimate objective of translating all optical measurements to the nanoscale. DOI FEATURE ARTICLEdiameter and not by the wavelength of the light. By scanning this aperture over a surface, it is possible to build up an optical image with resolution determined by the aperture diameter. Several review articles and texts have been written on this subject; readers interested in more details are directed to [ 1 , 7 ] and references therein. The idea for aperture-based sub-diffraction-limited optical imaging originated with Synge [ 8 ] in 1928, though the fi rst experimental results at optical frequencies were not published until 1984 by Pohl et al. [ 9 ] and Lewis et al. [ 10 ] Approximately eight years later, the fi rst fl uorescence images of single molecules were acquired using aperture NSOM. [ 11 ] In the most widely-adapted approach, a fi ber probe-consisting of a metal-coated tapered optical fi ber with the small aperture at the apex-is raster-scanned over the sample while maintaining a small tip-sample distance. [ 12 ] From a practical standpoint, however, this approach presents many complications. While aperture probes enable "background-free" imaging, where sample illumination occurs only within the nanoscale light spot created by the aperture probe, the boundary conditions for this type of waveguiding tip unfortunately demand that all propagating modes within the taper get cut off before reaching the aperture. This causes only evanescent waves to leak out from the end (see Figure 1 ). [ 13 ] Also, there is not signifi cant local electric fi eld enhancement at the aperture. These factors ultimately result in low optical throughput and signal strength. [ 13 , 14 ] In addition, because throughput is inversely proportional to the fourth power of the aperture radius, [ 14 ] signal-to-noise considerations in aperture NSOM ultimately constrain aperture size, and resolution, to ≈ 50-100 nm. In typical operation, the sample is either locally excited wi...

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Radiation Engineering of Optical Antennas for Maximum Field Enhancement

Cited by 188 publications

References 27 publications

Plasmonic Radiance: Probing Structure at the Ångström Scale with Visible Light

Plasmonic Radiance: Probing Structure at the Ångström Scale with Visible Light

Antenna Design for Directivity-Enhanced Raman Spectroscopy

Life Beyond Diffraction: Opening New Routes to Materials Characterization with Next‐Generation Optical Near‐Field Approaches

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