Polarization-dependent light extinction in ensembles of polydisperse, vertical semiconductor nanowires: A Mie scattering effective medium

We present an experimental and theoretical study of the angle- and polarization-dependent light extinction in random arrays of polydisperse semiconductor nanowires epitaxially grown on substrates. The specular reflectance is described by averaging the scattering properties of individual nanowires obtained from Lorenz-Mie theory over the diameter distribution. The complex effective refractive index describing the propagation and attenuation of the coherent beam scattered in forward direction is determined in the independent scattering approximation and used to calculate the angle- and polarization-dependent reflectance. Our measurements demonstrate the highly anisotropic scattering in ensembles of aligned nanowires

Motional narrowing of molecular vibrations strongly coupled to surface lattice resonances

We report on strong coupling between light in open cavities formed by arrays of gold microparticles and the carbonyl molecular vibration in poly(methyl methacrilate). These arrays sustain surface lattice resonances (SLRs), which are optical modes generated by the enhanced radiative coupling of the localized resonances in single scatterers by the diffraction in the array. Using the high-coherence beam of a free-electron laser, we measure the vibrational strong coupling and find a Rabi splitting into an upper and lower vibropolariton band. We observe the narrowing of the lower polariton band when the SLR is resonant with the molecular vibration. This behavior of the lower polariton linewidth can be modeled taking into account motional narrowing due to the spatial averaging of delocalized molecular vibrations in the strong coupling regime. The presence of motional narrowing in vibropolaritons in plasmonic arrays gives insight into the strong coupling of molecular vibrations, and introduces a different platform to investigate polaritonic chemistry, where reactions are not governed by individual molecules but by collective coupled vibrations.</p

Detection of deep-subwavelength dielectric layers at terahertz frequencies using semiconductor plasmonic resonators

Plasmonic bowtie antennas made of doped silicon can operate as plasmonic resonators at terahertz (THz) frequencies and provide large field enhancement close to their gap. We demonstrate both experimentally and theoretically that the field confinement close to the surface of the antenna enables the detection of ultrathin (100 nm) inorganic films, about 3750 times thinner than the free space wavelength. Based on model calculations, we conclude that the detection sensitivity and its variation with the thickness of the deposited layer are related to both the decay of the local THz field profile around the antenna and the local field enhancement in the gap of the bowtie antenna. This large field enhancement has the potential to improve the detection limits of plasmon-based biological and chemical sensors

Modified emission of extended light emitting layers by selective coupling to collective lattice resonances

We demonstrate that the coupling between light emitters in extended polymer layers and modes supported by arrays of plasmonic particles can be selectively enhanced by accurate positioning of the emitters in regions where the electric field intensity of a given mode is maximized. The enhancement, which we measure to reach up to 70%, is due to the improved spatial overlap and coupling between the optical mode and emitters. This improvement of the coupling leads to a modification of the emission spectrum and the luminous efficacy of the sample.Peer Reviewe

Control of the external photoluminescent quantum yield of emitters coupled to nanoantenna phased arrays

Optical losses in metals represent the largest limitation to the external quantum yield of emitters coupled to plasmonic antennas. These losses can be at the emission wavelength, but they can be more important at shorter wavelengths, i.e., at the excitation wavelength of the emitters, where the conductivity of metals is usually lower. We present accurate measurements of the absolute external photoluminescent quantum yield of a thin layer of emitting material deposited over a periodic nanoantenna phased array. Emission and absorptance measurements of the sample are performed using a custom-made setup including an integrating sphere and variable angle excitation. The measurements reveal a strong dependence of the external quantum yield on the angle at which the optical field excites the sample. Such behavior is attributed to the coupling between far-field illumination and near-field excitation mediated by the collective resonances supported by the array. Numerical simulations confirm that the inherent losses associated with the metal can be greatly reduced by selecting an optimum angle of illumination, which boosts the light conversion efficiency in the emitting layer. This combined experimental and numerical characterization of the emission from plasmonic arrays reveals the need to carefully design the illumination to achieve the maximum external quantum yieldPeer reviewe

Non-Equilibrium Bose–Einstein Condensation of Exciton-Polaritons in Silicon Metasurfaces

Exciton-polaritons (EPs) are hybrid light–matter quasi-particles with bosonic character formed by the strong coupling between excitons in matter and photons in optical cavities. Their hybrid character offers promising prospects for the realization of non-equilibrium Bose–Einstein condensates (BECs), and room-temperature BECs are possible with organic materials. However, the thresholds required to create BECs of organic EPs remain still high to allow condensation with electrical injection of carriers. One of the factors behind these high thresholds is the very short cavity lifetimes, leading to a fast EP decay and the need to inject higher exciton densities in the reservoir to form the condensate. Here a BEC of EPs in organic dyes and all-dielectric metasurfaces at room temperature is demonstrated. By using dielectric metasurfaces that exhibit very low losses it is possible to achieve cavity lifetimes long enough to allow an efficient population of EP states via vibrational relaxation and radiative pumping. It is shown how polariton lasing or non-equilibrium Bose–Einstein condensation is achieved in several cavities, and one of the lowest reported thresholds for BECs in organic materials is observed.</p