The lack of symmetry between electric and magnetic charges, a fundamental consequence of the small value of the fine-structure constant, is directly related to the weakness of magnetic effects in optical materials. Properly tailored plasmonic nanoclusters have been proposed recently to induce artificial optical magnetism based on the principle that magnetic effects are indistinguishable from specific forms of spatial dispersion of permittivity at optical frequencies. In a different context, plasmonic Fano resonances have generated a great deal of interest, particularly for use in sensing applications that benefit from sharp spectral features and extreme field localization. In the absence of natural magnetism, optical Fano resonances have so far been based on purely electric effects. In this Letter, we demonstrate that a subwavelength plasmonic metamolecule consisting of four closely spaced gold nanoparticles supports a strong magnetic response coupled to a broad electric resonance. Small structural asymmetries in the assembled nanoring enable the interaction between electric and magnetic modes, leading to the first observation of a magnetic-based Fano scattering resonance at optical frequencies. Our findings are supported by excellent agreement with simulations and analytical calculations, and represent an important step towards the quest for artificial magnetism and negative refractive index metamaterials at optical frequencies.

We discuss the possibility of realizing utlrabroadband omnidirectional absorbers and angularly selective coherent thermal emitters based on properly patterned plasmonic metastructures. Instead of relying on resonant concentration effects that inherently limit the bandwidth, we base our design on the combination of two inherently nonresonant effects: plasmonic

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We numerically study complex dual-interface grating systems to enhance absorption efficiency in thin-film silicon solar cells. We combine a plasmonic grating at the back side of the solar cell with a dielectric grating at the front side of the cell. We show a proof of principle, with one-dimensional gratings, that the distinctly different nature of the gratings can provide complementary enhancement mechanisms, which we further exploit by tailoring the specific periodicities, and by introducing blazing. Having different periods at specific interfaces allows for more efficient diffraction into both plasmonic and dielectric guided modes. In addition, grating specific blazing exposes extra modes to normal incident light through symmetry breaking. Multiple optimization routes are possible depending on the choice of photonic phenomena.

Unity transmittance at an interface between bulk media is quite common for polarized electromagnetic waves incident at the Brewster angle, but it is rarely observed for sound waves at any angle of incidence. In the following, we theoretically and experimentally demonstrate an acoustic metamaterial possessing a Brewster-like angle that is completely transparent to sound waves over an ultra-broadband frequency range with >100% bandwidth. The metamaterial, consisting of a hard metal with subwavelength apertures, provides a surface impedance matching mechanism that can be arbitrarily tailored to specific media. The nonresonant nature of the impedance matching effectively decouples the front and back surfaces of the metamaterial allowing one to independently tailor the acoustic impedance at each interface. On the contrary, traditional methods for acoustic impedance matching, for example in medical imaging, rely on resonant tunneling through a thin antireflection layer, which is inherently narrowband and angle specific.

Abstract:We theoretically investigate and compare the influence of square silver gratings and one-dimensional photonic crystal (1D PC) based nanostructures on the light absorption of organic solar cells with a thin active layer. We show that, by integrating the grating inside the active layer, excited localized surface plasmon modes may cause strong field enhancement at the interface between the grating and the active layer, which results in broadband absorption enhancement of up to 23.4%. Apart from using silver gratings, we show that patterning a 1D PC on top of the device may also result in a comparable broadband absorption enhancement of 18.9%. The enhancement is due to light scattering of the 1D PC, coupling the incoming light into 1D PC Bloch and surface plasmon resonance modes.

We report strong dissymmetry between left- and right-handed circularly polarized photoluminescence (PL) enhancement induced by 2D chiral gold nanostructures, which can be utilized to provide a circularly polarized luminescence source. Lightning-bolt-like (composed of two displaced rectangles) chiral plasmonic gold nanostructures were fabricated on a glass substrate and were adopted as materials to induce dissymmetry in PL enhancement. We employed achiral IR125 dye as an achiral molecular PL emitter with luminescence that was enhanced by near-field interaction between the chiral plasmon and the molecule. PL decay measurements confirmed that the PL enhancement arose from the plasmonic effect. Large PL enhancement dissymmetry factors g > 0.1 were obtained in the wavelength region near 800 nm. The dissymmetry of PL enhancement showed maximum amplitudes at 800–850 nm, which approximately correspond to the wavelength providing maximal extinction dissymmetry (∼800 nm), and is resonant with a chiral multipolar plasmon mode. The dissymmetry was relatively small at the wavelength resonant with a dipolar plasmon mode.

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