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Debabrata Biswas - One of the best experts on this subject based on the ideXlab platform.

  • shielding effects in random large area Field emitters the Field Enhancement factor distribution and current calculation
    Physics of Plasmas, 2018
    Co-Authors: Debabrata Biswas, Rashbihari Rudra
    Abstract:

    A finite-size uniform random distribution of vertically aligned Field emitters on a planar surface is studied under the assumption that the asymptotic Field is uniform and parallel to the emitter axis. A formula for Field Enhancement factor is first derived for a 2-emitter system and this is then generalized for N-emitters placed arbitrarily (line, array, or random). It is found that geometric effects dominate the shielding of Field lines. The distribution of Field Enhancement factor for a uniform random distribution of emitter locations is found to be closely approximated by an extreme value (Gumbel-minimum) distribution when the mean separation is greater than the emitter height but is better approximated by a Gaussian for mean separations close to the emitter height. It is shown that these distributions can be used to accurately predict the current emitted from a large area Field emitter.

  • shielding effects in random large area Field emitters the Field Enhancement factor distribution and current calculation
    Physics of Plasmas, 2018
    Co-Authors: Rashbihari Rudra, Debabrata Biswas
    Abstract:

    A finite-size uniform random distribution of vertically aligned Field emitters on a planar surface is studied under the assumption that the asymptotic Field is uniform and parallel to the emitter axis. A formula for Field Enhancement factor is first derived for a 2-emitter system and this is then generalized for N-emitters placed arbitrarily (line, array, or random). It is found that geometric effects dominate the shielding of Field lines. The distribution of Field Enhancement factor for a uniform random distribution of emitter locations is found to be closely approximated by an extreme value (Gumbel-minimum) distribution when the mean separation is greater than the emitter height but is better approximated by a Gaussian for mean separations close to the emitter height. It is shown that these distributions can be used to accurately predict the current emitted from a large area Field emitter.A finite-size uniform random distribution of vertically aligned Field emitters on a planar surface is studied under the assumption that the asymptotic Field is uniform and parallel to the emitter axis. A formula for Field Enhancement factor is first derived for a 2-emitter system and this is then generalized for N-emitters placed arbitrarily (line, array, or random). It is found that geometric effects dominate the shielding of Field lines. The distribution of Field Enhancement factor for a uniform random distribution of emitter locations is found to be closely approximated by an extreme value (Gumbel-minimum) distribution when the mean separation is greater than the emitter height but is better approximated by a Gaussian for mean separations close to the emitter height. It is shown that these distributions can be used to accurately predict the current emitted from a large area Field emitter.

  • a universal formula for the Field Enhancement factor
    Physics of Plasmas, 2018
    Co-Authors: Debabrata Biswas
    Abstract:

    The Field Enhancement factor (FEF) is an important quantity in Field emission calculations since the tunneling electron current depends very sensitively on its magnitude. The exact dependence of FEF on the emitter height h, the radius of curvature at the apex Ra, as well as the shape of the emitter base are still largely unknown. In this work, a universal formula for the Field Enhancement factor is derived for a single emitter. It depends on the ratio h/Ra and has the form γ a = ( 2 h / R a ) / [ α 1 ln ( 4 h / R a ) − α 2 ], where α1 and α2 depend on the charge distribution on the emitter. Numerical results show that a simpler form γ a = ( 2 h / R a ) / [ ln ( 4 h / R a ) − α ] is equally valid with α depending on the emitter-base. Thus, for the hyperboloid, conical, and ellipsoid emitters, the value of α is 0, 0.88, and 2, while for the cylindrical base, α ≃ 2.6.

  • A universal formula for the Field Enhancement factor
    Physics of Plasmas, 2018
    Co-Authors: Debabrata Biswas
    Abstract:

    The Field Enhancement factor (FEF) is an important quantity in Field emission calculations since the tunneling electron current depends very sensitively on its magnitude. The exact dependence of FEF on the emitter height $h$, the radius of curvature at the apex $R_a$, as well as the shape of the emitter base is still largely unknown. In this work, a universal formula for the Field Enhancement factor is derived. It depends on the ratio $h/R_a$ and has the form $\gamma_a = (2h/R_a)/[\alpha_1 \log(4h/R_a) - \alpha_2 ]$ where $\alpha_1$, $\alpha_2$ depend on the charge distribution on the emitter. Numerical results show that a simpler form $\gamma_a = (2h/R_a)/[\log(4h/R_a) - \alpha]$ is equally valid with $\alpha$ depending on the class of emitter and indicative of the shielding by the emitter-base. For the hyperboloid, conical and ellipsoid emitters, the value of $\alpha$ is $0, 0.88$ and $2$ while for the cylindrical base where shielding is minimum, $\alpha \simeq 2.6$.

Kenneth B Crozier - One of the best experts on this subject based on the ideXlab platform.

  • optical antennas integrated with concentric ring gratings electric Field Enhancement and directional radiation
    Optics Express, 2011
    Co-Authors: Dongxing Wang, Tian Yang, Kenneth B Crozier
    Abstract:

    We describe a means for improving the coupling of illumination to, and the collection of scattered radiation from, an optical antenna. This is achieved by integrating optical antennas with concentric ring gratings. Electromagnetic simulations demonstrate that the ring grating improves the coupling to the antenna, even if the incident illumination is focused by an aplanatic lens such as a microscope objective. Dipole radiation from the center of the structure is well collimated. Various aspects of Field Enhancement and dipole radiation behavior are analyzed. We propose this device for Raman scattering Enhancement.

  • Charge and current reservoirs for electric and magnetic Field Enhancement
    Opt. Express, 2010
    Co-Authors: Dongxing Wang, Tian Yang, Kenneth B Crozier
    Abstract:

    Two optical antenna designs incorporating structures termed charge and current reservoirs are proposed to realize localized high electric and magnetic Field Enhancement, respectively. Simulation results show that the fan-rod electric antenna design combines the advantages of the rod antenna and the bowtie antenna, and has higher Field Enhancement than either. The performance of a loop shaped magnetic antenna consisting of a pair of metallic strips with offsets is also verified numerically, with high magnetic Field Enhancement being observed in the simulation. In both of the designs, the concepts of charge and current reservoirs contribute to high electric and magnetic Field Enhancement.

  • Field Enhancement and gap dependent resonance in a system of two opposing tip to tip au nanotriangles
    Physical Review B, 2005
    Co-Authors: A Sundaramurthy, Kenneth B Crozier, P J Schuck, G S Kino, D P Fromm, W E Moerner
    Abstract:

    The Enhancement of the electromagnetic Field is described for nanoscale metallic “bowtie” antennas, consisting of two opposing tip-to-tip Au nanotriangles separated by a gap, through simulation and experiment. Currents, Field distributions, and scattering efficiencies in the antennas at optical wavelengths are obtained from finite-difference time-domain FDTD simulations using realistic wavelength-dependent dielectric constants. The experimentally measured resonant wavelengths and intensity Enhancements from individual bowtie antennas are in excellent agreement with the FDTD simulations. A simple physical model based on current distribution in the antennas is presented to understand the variation in resonant wavelength with gap and explain the basis for the Field Enhancement.

  • optical antennas resonators for local Field Enhancement
    Journal of Applied Physics, 2003
    Co-Authors: Kenneth B Crozier, A Sundaramurthy, G S Kino, C F Quate
    Abstract:

    Electromagnetic Field Enhancement in optical antenna arrays is studied by simulation and experiment at midinfrared wavelengths. The optical antennas are designed to produce intense optical Fields confined to subwavelength spatial dimensions when illuminated at the resonant wavelength. Finite difference time domain (FDTD) method simulations are made of the current, charge, and Field distributions in the antennas. The influence of antenna shape, length, and sharpness upon the intensity of the optical Fields produced is found. Optical antennas arrays are fabricated on transparent substrates by electron beam lithography. Far-Field extinction spectroscopy carried out on the antenna arrays shows the dependence of the resonant wavelength on the antenna length and material. The FDTD calculated and experimentally measured extinction efficiencies of the optical antennas are found to be in good agreement.

Martijn Wubs - One of the best experts on this subject based on the ideXlab platform.

  • modified Field Enhancement and extinction by plasmonic nanowire dimers due to nonlocal response
    Optics Express, 2012
    Co-Authors: Giuseppe Toscano, Soren Raza, Anttipekka Jauho, Asger N Mortensen, Martijn Wubs
    Abstract:

    We study the effect of nonlocal optical response on the optical properties of metallic nanowires, by numerically implementing the hydrodynamical Drude model for arbitrary nanowire geometries. We first demonstrate the accuracy of our frequency-domain finite-element implementation by benchmarking it in a wide frequency range against analytical results for the extinction cross section of a cylindrical plasmonic nanowire. Our main results concern more complex geometries, namely cylindrical and bow-tie nanowire dimers that can strongly enhance optical Fields. For both types of dimers we find that nonlocal response can strongly affect both the Field Enhancement in between the dimers and their respective extinction cross sections. In particular, we give examples of blueshifted maximal Field Enhancements near hybridized plasmonic dimer resonances that are still large but nearly two times smaller than in the usual local-response description. For the same geometry at a fixed frequency, the Field Enhancement and cross section can also be significantly more enhanced in the nonlocal-response model.

  • modified Field Enhancement in plasmonic nanowire dimers due to nonlocal response
    arXiv: Mesoscale and Nanoscale Physics, 2011
    Co-Authors: Giuseppe Toscano, Soren Raza, Anttipekka Jauho, Asger N Mortensen, Martijn Wubs
    Abstract:

    We study the effect of nonlocal optical response on the optical properties of metallic nanowires, by numerically i mplementing the hydrodynamical Drude model for arbitrary nanowire geometries. We first demonstrate the accuracy of our frequency-domain finite-el ement imple- mentation by benchmarking it in a wide frequency range against analytical results for the extinction cross section of a cylindrical pl asmonic nanowire. Our main results concern more complex geometries, namely cylindrical and bow-tie nanowire dimers that can strongly enhance optical fi elds. For both types of dimers we find that nonlocal response can strongly af fect both the Field Enhancement in between the dimers and their respective extinction cross sections. In particular, we give examples of maximal fi eld enhance- ments near hybridized plasmonic dimer resonances that are still large but nearly two times smaller than in the usual local-response description. At the same time, for a fixed frequency the Field Enhancement and cros s section can also be significantly more enhanced in the nonlocal-resp onse model.

Chengsheng Gong - One of the best experts on this subject based on the ideXlab platform.

  • narrow band perfect absorber for maximum localized magnetic and electric Field Enhancement and sensing applications
    Scientific Reports, 2016
    Co-Authors: Zhengdong Yong, Senlin Zhang, Chengsheng Gong
    Abstract:

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong Field Enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic Field Enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and Field Enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10(-4) × (λres/n)(3). Based on the coupled mode theory, we verify that the diluted Field Enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum Field Enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local Field Enhancement, and has potential applications in biosensors, filters and nonlinear optics.

  • narrow band perfect absorber for maximum localized magnetic and electric Field Enhancement and sensing applications
    arXiv: Optics, 2016
    Co-Authors: Zhengdong Yong, Senlin Zhang, Chengsheng Gong
    Abstract:

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong Field Enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic Field Enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and Field Enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10^-4*({\lambda}/n)^3 . Based on the coupled mode theory, we verify that the diluted Field Enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum Field Enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local Field Enhancement, and has potential applications in biosensors, filters and nonlinear optics.

Giuseppe Toscano - One of the best experts on this subject based on the ideXlab platform.

  • modified Field Enhancement and extinction by plasmonic nanowire dimers due to nonlocal response
    Optics Express, 2012
    Co-Authors: Giuseppe Toscano, Soren Raza, Anttipekka Jauho, Asger N Mortensen, Martijn Wubs
    Abstract:

    We study the effect of nonlocal optical response on the optical properties of metallic nanowires, by numerically implementing the hydrodynamical Drude model for arbitrary nanowire geometries. We first demonstrate the accuracy of our frequency-domain finite-element implementation by benchmarking it in a wide frequency range against analytical results for the extinction cross section of a cylindrical plasmonic nanowire. Our main results concern more complex geometries, namely cylindrical and bow-tie nanowire dimers that can strongly enhance optical Fields. For both types of dimers we find that nonlocal response can strongly affect both the Field Enhancement in between the dimers and their respective extinction cross sections. In particular, we give examples of blueshifted maximal Field Enhancements near hybridized plasmonic dimer resonances that are still large but nearly two times smaller than in the usual local-response description. For the same geometry at a fixed frequency, the Field Enhancement and cross section can also be significantly more enhanced in the nonlocal-response model.

  • modified Field Enhancement in plasmonic nanowire dimers due to nonlocal response
    arXiv: Mesoscale and Nanoscale Physics, 2011
    Co-Authors: Giuseppe Toscano, Soren Raza, Anttipekka Jauho, Asger N Mortensen, Martijn Wubs
    Abstract:

    We study the effect of nonlocal optical response on the optical properties of metallic nanowires, by numerically i mplementing the hydrodynamical Drude model for arbitrary nanowire geometries. We first demonstrate the accuracy of our frequency-domain finite-el ement imple- mentation by benchmarking it in a wide frequency range against analytical results for the extinction cross section of a cylindrical pl asmonic nanowire. Our main results concern more complex geometries, namely cylindrical and bow-tie nanowire dimers that can strongly enhance optical fi elds. For both types of dimers we find that nonlocal response can strongly af fect both the Field Enhancement in between the dimers and their respective extinction cross sections. In particular, we give examples of maximal fi eld enhance- ments near hybridized plasmonic dimer resonances that are still large but nearly two times smaller than in the usual local-response description. At the same time, for a fixed frequency the Field Enhancement and cros s section can also be significantly more enhanced in the nonlocal-resp onse model.