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.

Direct near-field optical imaging of plasmonic resonances in metal nanoparticle pairs

Abstract: In this paper we investigate the near-field optical behavior of plasmon coupling in gold nanoparticle pairs. In particular, by performing series measurements through a fiber-collection mode near-field scanning optical microscope (NSOM), we directly observed the localized electromagnetic (EM) field distribution between two nanospheres is sensitively depended on the incident polarization and interparticle distance. The qualitative near-field observation and quantitative analysis facilitate more understanding of localized hot spots in surface-enhanced Raman scattering (SERS), and nano-applications in selectively controlling the spatial distribution of localized surface plasmon (SP) modes on a fabricated nanostructure by adjusting the polarization direction.

The Optical Chirality Flux as a Useful Far-Field Probe of Chiral Near Fields

Abstract: To optimize the interaction between chiral matter and highly twisted light, quantities that can help characterize chiral electromagnetic fields near nanostructures are needed. Here, by analogy with Poynting's theorem, we formulate the time-averaged conservation law of optical chirality in lossy dispersive media and identify the optical chirality flux as an ideal far-field observable for characterizing chiral optical near fields. Bounded by the conservation law, we show that it provides precise information, unavailable from circular dichroism spectroscopy, on the magnitude and handedness of highly twisted fields near nanostructures.

Design and fabrication of low beam divergence and high kink-free power lasers

Abstract: We report the design and fabrication of high performance high power lasers with emission wavelength from 800 to 1000 nm using a novel wafer structure, in which a graded V-shape layer was incorporated, to reduce the vertical far field (wafer growth direction) and to suppress higher order mode lasing. The structure offers the freedom to independently design the vertical far field and optical overlap with the quantum wells. An extremely low far field can be achieved, which still retains high optical overlap, allowing a low threshold current to be maintained. In addition, the structure can greatly enhance the laser kink-free power by suppressing or even completely eliminating higher order mode lasing, an extremely desirable property for high power single mode lasers.

Sound field separation technique based on equivalent source method and its application in nearfield acoustic holography.

Abstract: A technique for separating sound fields using two closely spaced parallel measurement surfaces and based on equivalent source method is proposed. The method can separate wave components crossing two measurement surfaces in opposite directions, which makes nearfield acoustic holography (NAH) applications in a field where there exist sources on the two sides of the hologram surface, in a reverberant field or in a scattered field, possible. The method is flexible in applications, simple in computation, and very easy to implement. The measurement surfaces can be arbitrarily shaped, and they are not restricted to be regular as in the traditional field separation technique. And, because the method performs field separation calculations directly in the spatial domain-not in the wave number domain--it avoids the errors and limitations (the window effects, etc.) associated with the traditional field separation technique based on the spatial Fourier transform method. In the paper, a theoretical description is first given, and the performance of the proposed field separation technique and its application in NAH are then evaluated through experiments.

Propagation of a stochastic electromagnetic vortex beam in the oceanic turbulence

Abstract: By using the extended Huygens–Fresnel principle, we investigate the stochastic electromagnetic vortex beam propagating through oceanic turbulence. General formulas for the elements of the 2×2 cross-spectral density matrix of a stochastic electromagnetic vortex beam propagating through the oceanic turbulence are obtained. We study the changes in the spectral density, the spectral degree of coherence and the spectral degree of polarization of such a vortex beam with the help of the general formulas. It is shown by numerical calculations that, the beam profile will approach a Gaussian distribution in far field under the influence of oceanic turbulence. It is also interesting to find that the spectral degree of polarization of a stochastic electromagnetic vortex beam composed by isotropic sources on propagation in far zone will return to its value in the source plane.