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Register a new userNear-field Holographic Retrieval of an Isolated Subwavelength Hole in a Thin Metallic Film
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Using a holographic approach, we experimentally study the near-field intensity distribution of light squeezed through an isolated subwavelength plasmonic hole in a thin metallic film. Our experiments revealed an in-plane electric dipole moment excited near the isolated hole. By analyzing the fringe patterns formed between the in-plane dipole and plane wave illumination, both the transmission coefficient and phase shift of the dipole can be retrieved. We also observed opposite phases of the excited dipoles from the subwavelength dent and protrusion in the metallic film, in good agreement with the prediction from our model. Our approach can be used to study the microscopic process of the light-structure interaction for the plasmonic and nanophotonic systems with potential applications in high density optical data storages.
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y coating a cover layer with metallization of cut wire array, the transmission of transverse electric waves (TE; the electric field is parallel to the slits) through subwavelength slits in a thin metallic film is significantly enhanced. An 800-fold enhanced transmission is obtained compared to the case without the cut wires. It is demonstrated that a TE incident wave is highly confined by the cut wires due to the excitation of the electric dipole-like resonance, and then effectively squeezed into and through the subwavelength slits.
Modern scattering-type scanning near-field optical microscopy (s-SNOM) has become an indispensable tool in material research. However, as the s-SNOM technique marches into the far-infrared (IR) and terahertz (THz) regimes, emerging experiments sometimes produce puzzling results. For example, anomalies in the near-field optical contrast have been widely reported. In this Letter, we systematically investigate a series of extreme subwavelength metallic nanostructures via s-SNOM near-field imaging in the GHz to THz frequency range. We find that the near-field material contrast is greatly impacted by the lateral size of the nanostructure, while the spatial resolution is practically independent of it. The contrast is also strongly affected by the connectivity of the metallic structures to a larger metallic ground plane. The observed effect can be largely explained by a quasi-electrostatic analysis. We also compare the THz s-SNOM results to those of the mid-IR regime, where the size-dependence becomes significant only for smaller structures. Our results reveal that the quantitative analysis of the near-field optical material contrasts in the long-wavelength regime requires a careful assessment of the size and configuration of metallic (optically conductive) structures.
Proposed all optical amplification scenario is based on the properties of light propagation in two coupled subwavelength metallic slab waveguides where for particular choice of waveguide parameters two propagating (symmetric) and non-propagating (antisymmetric) eigenmodes coexist. For such a setup incident beams realize boundary conditions for forming a stationary state as a superposition of mentioned eigenmodes. It is shown both analytically and numerically that amplification rate in this completely linear mechanism diverges for small signal values.
In this Letter we experimentally demonstrate that the radiative heat transfer between metallic planar surfaces exceeds the blackbody limit by employing the near-field and thin-film effects. Nanosized polystyrene particles were used to create a nanometer gap between aluminum thin-films of different thicknesses coated on 5x5 mm2 diced silicon chips while the gap spacing is fitted from the near-field measurement with bare Si chips. The experimental results are validated by theoretical calculation based on fluctuational electrodynamics. The near-field radiative heat flux between 13-nm Al thin-film samples at 215 nm gap distance is measured to be 6.4 times over the blackbody limit and 420 times compared to the far-field radiative heat transfer between metallic surfaces with a temperature difference of 65 K. In addition, the theoretical prediction suggests a near-field enhancement of 122 times relative to the blackbody limit and 8000 times over far-field one at 50-nm vacuum gap between 20-nm Al thin-film samples, under the same temperature difference of 65 K. This work will facilitate the understanding and application of near-field radiation to thermal power conversion, noncontact cooling, heat flow management, and optical storage where metallic materials are involved.
We report single-mode lasing in subwavelength GaAs disks under optical pumping. The disks are fabricated by standard photolithography and two steps of wet chemical etching. The simple fabrication method can produce submicron disks with good circularity, smooth boundary and vertical sidewalls. The smallest lasing disks have a diameter of 627 nm and thickness of 265 nm. The ratio of the disk diameter to the vacuum lasing wavelength is about 0.7. Our numerical simulations confirm that the lasing modes are whispering-gallery modes with the azimuthal number as small as 4 and very small mode volume.
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