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Bryant, Garnett W.; García de Abajo, F. Javier; Aizpurua, Javier |
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Title |
Mapping the Plasmon Resonances of Metallic Nanoantennas |
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Journal Article |
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2008 |
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Nano Letters |
Abbreviated Journal |
Nano Lett. |
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5 |
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2 |
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631-636 |
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Keywords |
optical antennas |
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Abstract |
We study the light scattering and surface plasmon resonances of Au nanorods that are commonly used as optical nanoantennas in analogy to dipole radio antennas for chemical and biodetection field-enhanced spectroscopies and scanned-probe microscopies. With the use of the boundary element method, we calculate the nanorod near-field and far-field response to show how the nanorod shape and dimensions determine its optical response. A full mapping of the size (length and radius) dependence for Au nanorods is obtained. The dipolar plasmon resonance wavelength λ shows a nearly linear dependence on total rod length L out to the largest lengths that we study. However, L is always substantially less than λ/2, indicating the difference between optical nanoantennas and long-wavelength traditional λ/2 antennas. Although it is often assumed that the plasmon wavelength scales with the nanorod aspect ratio, we find that this scaling does not apply except in the extreme limit of very small, spherical nanoparticles. The plasmon response depends critically on both the rod length and radius. Large (500 nm) differences in resonance wavelength are found for structures with different sizes but with the same aspect ratio. In addition, the plasmon resonance deduced from the near-field enhancement can be significantly red-shifted due to retardation from the resonance in far-field scattering. Large differences in near-field and far-field response, together with the breakdown of the simple scaling law must be accounted for in the choice and design of metallic λ/2 nanoantennas. We provide a general, practical map of the resonances for use in locating the desired response for gold nanoantennas. |
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RPLAB @ gujma @ |
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737 |
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Author |
Codreanu, Iulian; Boreman, Glenn D. |
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Title |
Infrared microstrip dipole antennas |
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Journal Article |
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2001 |
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Microwave and Optical Technology Letters |
Abbreviated Journal |
Microw Opt Technol Lett |
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29 |
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6 |
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381-383 |
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optical antennas |
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Abstract 10.1002/mop.1184.abs We report on the successful use of niobium microbolometers coupled to microstrip dipole antennas for the detection of midinfrared radiation. Measurements of the detector response versus antenna length performed at the 10.6 μm wavelength allowed us to identify the first three current-wave resonances along the antenna arms. The detector response was also measured as a function of the radiation wavelength in the 911 μm spectral domain. Excellent agreement between the experimental results and finite-difference time-domain (FDTD) predictions was obtained. |
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RPLAB @ gujma @ |
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738 |
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González, F. J.; Boreman, G. D. |
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Title |
Comparison of dipole, bowtie, spiral and log-periodic IR antennas |
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Journal Article |
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2005 |
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Infrared Physics & Technology |
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Inf Phys & Technol |
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46 |
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5 |
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418-428 |
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optical antennas; Microbolometer; Infrared antennas; Antenna efficiency; Antenna-coupled detectors |
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Antenna-coupled microbolometers use planar lithographic antennas to couple infrared radiation into a bolometer with sub-micron dimensions. In this paper four different types of infrared antennas were fabricated on thin grounded-substrates and coupled to microbolometers. Dipole, bowtie, spiral and log-periodic IR antenna-coupled detectors were measured at 10.6 μm and their performance compared. A new method to calculate the radiation efficiency based on the spatial and angular response of infrared antennas is presented and used to evaluate their performance. The calculated radiation efficiency for the dipole, bowtie, spiral and log-periodic IR antennas was 20%, 37%, 25% and 46% respectively. A dipole-length study was performed and shows that the quasistatic value of the effective permittivity accurately describes the incident wavelength in the substrate at infrared frequencies for antennas on a thin substrate. |
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RPLAB @ gujma @ |
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739 |
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Author |
Gonzalez, F.J.; Ilic, B.; Alda, J.; Boreman, G.D. |
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Title |
Antenna-coupled infrared detectors for imaging applications |
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2005 |
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IEEE J. Sel. Topics Quantum Electron. |
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11 |
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1 |
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117 - 120 |
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Keywords |
optical antennas |
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Infrared focal plane arrays (IRFPAs) are a critical component in advanced infrared imaging systems. IRFPAs are made up of two parts, a detector array and a readout integrated circuit (ROIC) multiplexer. Current ROIC technology has typical pitch sizes of 20×20 to 50×50 μm2. In order to make antenna-coupled detectors suited for infrared imaging systems, two-dimensional (2-D) arrays have been fabricated that cover a whole pixel area with the penalty of increasing the noise figure of the detector and, therefore, reducing its performance. By coupling a Fresnel zone plate lens to a single element antenna-coupled detector, infrared radiation can be collected over a typical pixel area and still keep low-noise levels. A Fresnel zone plate lens coupled to a single-element square-spiral-coupled infrared detector has been fabricated and its performance compared to single element antenna-coupled detectors and 2-D arrays of antenna coupled detectors. Measurements made at 10.6 μm showed a two-order-of-magnitude increase in SNR and a ~× increase in D* as compared to 2-D arrays of antenna-coupled detectors. |
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RPLAB @ gujma @ |
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741 |
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González, Francisco Javier; Alda, Javier; Ilic, Bojan; Boreman, Glenn D. |
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Title |
Infrared Antennas Coupled to Lithographic Fresnel Zone Plate Lenses |
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Journal Article |
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2004 |
Publication |
Applied Optics |
Abbreviated Journal |
Appl. Opt. |
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Volume |
43 |
Issue |
33 |
Pages |
6067-6073 |
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Keywords |
optical antennas |
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Several designs for Fresnel zone plate lenses (FZPLs) to be used in conjunction with antenna-coupled infrared detectors have been fabricated and tested. The designs comprise square and circular FZPLs with different numbers of Fresnel zones working in transmissive or reflective modes designed to focus infrared energy on a square-spiral antenna connected to a microbolometer. A 163× maximum increase in response was obtained from a 15-zone circular FZPL in the transmissive mode. Sensor measurements of normalized detectivity D* resulted in a 2.67× increase with FZPLs compared with measurements made of square-spiral antennas without FZPLs. The experimental results are discussed and compared with values obtained from theoretical calculations. |
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RPLAB @ gujma @ |
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740 |
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