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Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.


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Journal ArticleDOI
TL;DR: In this paper, the optical properties of metal-dielectric-metal structures with patterned top metallic surfaces, in the THz frequency range, were studied and a detailed analysis of the physical mechanisms which give rise to these photonic modes were provided.
Abstract: We present an experimental and theoretical study of the optical properties of metal-dielectric-metal structures with patterned top metallic surfaces, in the THz frequency range. When the thickness of the dielectric slab is very small with respect to the wavelength, these structures are able to support strongly localized electromagnetic modes, concentrated in the subwavelength metal-metal regions. We provide a detailed analysis of the physical mechanisms which give rise to these photonic modes. Furthermore, our model quantitatively predicts the resonance positions and their coupling to free space photons. We demonstrate that these structures provide an efficient and controllable way to convert the energy of far field propagating waves into near field energy.

115 citations

Journal ArticleDOI
TL;DR: In this paper, a method based on Lorentz-reciprocity theorem is proposed to calculate the free-space and guided radiation diagrams with a high accuracy from the sole knowledge of the near-field around the emitters or scatterers.
Abstract: Light emitters or scatterers embedded in stratified media may couple energy to both free space modes and guided modes of the stratified structure. For a comprehensive analysis, it is important to evaluate the angular intensity distribution of both the free-space modes and guided modes excited in such systems. In the present work, we propose an original method based on Lorentz-reciprocity theorem to efficiently calculate the free-space and guided radiation diagrams with a high accuracy from the sole knowledge of the near-field around the emitters or scatterers. Compared to conventional near-to-far field transformation techniques, the proposal allows one to easily evaluate the guided-mode radiation diagrams, even if material dissipation is present in the stack, and thus to simultaneously track the coupling of light to all channels (i.e., free-space and guided-ones). We also provide an open-source code that may be used with essentially any Maxwell's equation solver. The numerical tool may help to engineer various devices, such as light-emitting diodes or nanoantennas to achieve directional and efficient radiative spontaneous decays in free space and guided optics.

114 citations

Journal ArticleDOI
TL;DR: In this article, the axial dependence of the plasma density, electron temperature, plasma potentials, and the 488 nm argon ion emission intensity have been measured in argon helicon discharges excited by both right helical and Nagoya III antennas for various magnitudes and directions of the magnetic field B.
Abstract: The axial dependence of the plasma density, electron temperature, plasma potentials, and the 488 nm argon ion emission intensity have been measured in argon helicon discharges excited by both right helical and Nagoya III antennas for various magnitudes and directions of the magnetic field B. The plasma parameters were monitored with RF-compensated probes, while the emission line was detected with an optical emission spectrometer that incorporates an optical fibre and a miniature lens. The right helical antennas were designed to excite the m = +1 azimuthal mode when B is parallel () to the propagation vector k, and the m = -1 mode when B is antiparallel (#) to k. The plasma is found to be more dense in the former case (, m = +1), and the density peaks several antenna lengths downstream in the k direction. Nagoya III antennas are symmetric antennas that should excite the same azimuthal mode content in either magnetic field direction; indeed, the light profile was found to be independent of field direction. In the near field, under the antennas, the density is approximately the same for both antenna geometries and magnetic field directions. These results indicate that the m = +1 mode is preferentially excited regardless of the antenna helicity.

114 citations

Book ChapterDOI
01 Jan 2009

114 citations

Journal ArticleDOI
TL;DR: In this article, a new variety of millimeter-wave Fresnel-zone plate lens with enhanced focusing quality is described, where each full-wave zone of the lens is divided into four quarter-wave subzones, which are covered by dielectric rings having equal thickness but different permittivities.
Abstract: A new variety of millimeter-wave Fresnel-zone plate lens with enhanced focusing quality is described Each full-wave zone of the lens is divided into four quarter-wave subzones, which are covered by dielectric rings having equal thickness but different permittivities More practical equations are derived for the radii of the zones, and for the thickness of the lens by taking into account the angle of incidence of the electromagnetic wave A Fresnel-zone plate antenna (FZPA) consisting of a quarterwave lens and a scalar feed is developed and analysed theoretically Equations for the aperture field and far field are derived using multiple ray tracing through dielectric plates and vectorial Kirchhoff diffraction theory, respectively It is demonstrated that the proposed transmissive-type FZPA has an aperture efficiency of more than 50% in the 60 GHz frequency band This computed efficiency agree with the measured overall efficiency reported by other researchers for an X-band quarter-wave reflector-type FZPA

114 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023132
2022281
2021376
2020460
2019640
2018604