Light sources based on reliable and energy-efficient light-emitting diodes (LEDs) are instrumental in the development of solid-state lighting (SSL). Most research efforts in SSL have focused on improving both the intrinsic quantum efficiency (QE) and the stability of light emitters. For this reason, it is broadly accepted that with the advent of highly efficient (QE close to 1) and stable emitters, the fundamental research phase of SSL is coming to an end. In this study, we demonstrate a very large improvement in SSL emission (above 70-fold directional enhancement for p-polarized emission and 60-fold enhancement for unpolarized emission) using nanophotonic structures. This is attained by coupling emitters with very high QE to collective plasmonic resonances in periodic arrays of aluminum nanoantennas. Our results open a new path for fundamental and applied research in SSL in which plasmonic nanostructures are able to mold the spectral and angular distribution of the emission with unprecedented precision.

Metallic nanostructures provide a toolkit for the generation of coherent light below the diffraction limit. Plasmonicbased lasing relies on the population inversion of emitters (such as organic fluorophores) along with feedback provided by plasmonic resonances. In this regime, known as weak light-matter coupling, the radiative characteristics of the system can be described by the Purcell effect. Strong light-matter coupling between the molecular excitons and electromagnetic field generated by the plasmonic structures leads to the formation of hybrid quasi-particles known as plasmon-exciton-polaritons (PEPs). Due to the bosonic character of these quasi-particles, exciton-polariton condensation can lead to laser-like emission at much lower threshold powers than in conventional photon lasers. Here, we observe PEP lasing through a dark plasmonic mode in an array of metallic nanoparticles with a low threshold in an optically pumped organic system. Interestingly, the threshold power of the lasing is reduced by increasing the degree of light-matter coupling in spite of the degradation of the quantum efficiency of the active material, highlighting the ultrafast dynamic responsible for the lasing, i.e., stimulated scattering. These results demonstrate a unique roomtemperature platform for exploring the physics of exciton-polaritons in an open-cavity architecture and pave the road toward the integration of this on-chip lasing device with the current photonics and active metamaterial planar technologies.

We demonstrate an improvement by more than 1 order of magnitude of the figure of merit (FoM) of plasmonic nanoparticle sensors by means of the diffractive coupling of localized surface plasmon resonances. The coupling in arrays of nanoparticles leads to Fano resonances with narrow line widths known as surface lattice resonances, which are very suitable for the sensitive detection of small changes in the refractive index of the surroundings. We focus on the sensitivity to the bulk refractive index and find that the sensor FoM scales solely with the frequency difference between the surface lattice resonance and the diffracted order grazing to the surface of the array. This result, which can be extended to other systems with coupled resonances, enables the design of plasmonic sensors with a high FoM over broad spectral ranges with unprecedented accuracy.

We experimentally explore the dynamic optical hysteresis of a semiconductor microcavity as a function of the sweep time. The hysteresis area exhibits a double power law decay due to the shot noise of the driving laser, which triggers switching between metastable states. Upon increasing the average photon number and approaching the thermodynamic limit, the double power law evolves into a single power law. This algebraic behavior characterizes a dissipative phase transition. Our findings are in good agreement with theoretical predictions, and the present experimental approach is promising for the exploration of critical phenomena in photonic lattices.Optical bistability -the existence of two stable states with different photon numbers for the same driving conditions -is a general feature of driven nonlinear systems described within the mean-field approximation (MFA) [1]. Beyond the MFA, a quantum treatment predicts that the steady-state of a nonlinear cavity is unique at any driving condition [2]. The origin of this apparent contradiction was noted by Bonifacio and Lugiato [3], and by Drummond and Walls [4]: quantum fluctuations (the lost feature in the MFA) trigger switching between states and the exact solution corresponds to a weighted average over the two metastable states. Experiments in the 80's with two-mode lasers evidenced extremely long switching times [5], which were predicted to diverge for weak fluctuations and/or large photon numbers [6]. Already in these early works, this dramatic slowing down of the system dynamics was linked to a first order phase transition [5][6][7].The physics of nonlinear resonators is receiving renewed interest in connection to predictions of quantum many-body phases [8][9][10][11][12][13], critical phenomena [5,[12][13][14][16][17][18], and dissipative phase transitions [4]. Impressive progress is being made in building lattices of nonlinear resonators, such as photonic crystal cavities [20,21], waveguides [22], superconducting microwave resonators [23,24], or optomechanical resonators [25,26]. In this context, semiconductor microcavities operating in the exciton-photon strong coupling regime provide a versatile platform where photon hopping and the pumping geometry can be controlled [27]. Lattices of different dimensionalities can be engineered [28,29], and the hybrid light-matter nature of their elementary excitations, namely cavity polaritons, provide a strong and tunable Kerr nonlinearity via the exciton component [1,[30][31][32].Recently, it was predicted that even in a single resonator, critical exponents could be retrieved from dynamical hysteresis measurements [17]. More precisely, when the driving power is swept at a finite speed across a bistability, the area of the hysteresis cycle is expected to close following a double power-law as a function of the sweep time [5, 6]. The long-time decay arises from quantum fluctuations, and presents a universal −1 exponent [5]. In the thermodynamic limit wherein the photon number in the bistability tends to infinity and fluctua...

We demonstrate the coupling of bright and dark surface lattice resonances (SLRs), which are collective Fano resonances in 2D plasmonic crystals. As a result of this coupling, a frequency stop gap in the dispersion relation of SLRs is observed. The different field symmetries of the low-and high-frequency SLR bands lead to pronounced differences in their coupling to free-space radiation. Standing waves of very narrow spectral width compared to localized surface-plasmon resonances are formed at the highfrequency band edge, while subradiant damping onsets at the low-frequency band edge, leading the resonance into darkness. We introduce a coupled-oscillator analog to the plasmonic crystal, which serves to elucidate the physics of the coupled plasmonic resonances and which is used to estimate very high quality factors for SLRs. DOI: 10.1103/PhysRevX.1.021019 Subject Areas: Nanophysics, PlasmonicsMetallic nanoparticles supporting surface-plasmon resonances allow light to be localized in nanoscale volumes, thereby opening exciting possibilities such as nanoscale control of emitters [1], large electromagnetic enhancements [2], and nonlinear nano-optics [3]. Much attention has been given to localized surface-plasmon resonances (LSPRs), which arise in individual particles when their conduction electrons are coherently driven by an electromagnetic field. Although localized surface plasmons in neighbor particles may mutually couple, their resonances are, in general, severely broadened due to strong radiative damping. Hence, LSPRs exhibit low quality factors Q. A recent development in nanoplasmonics deals with collective resonances in periodic arrays of metallic nanostructures, or plasmonic crystals. Such arrays support surface lattice resonances (SLRs), which are collective resonances mediated by diffractive coupling of localized plasmons. This coupling occurs near the critical frequency at which a diffraction order is radiating in the plane of the array, i.e., at the Rayleigh anomaly. SLRs were introduced by Carron [4], and the interest in this phenomenon was revived by Schatz and co-workers with a series of works on 1D and 2D arrays [5,6]. However, the experimental observation of SLRs remained elusive for many years [7]. Recent advances in nanofabrication and in the understanding of SLRs have allowed for their observation in periodic arrays of nanostructures with different geometries [8][9][10][11][12][13]. In contrast with LSPRs, SLRs possess much higher Q's, and the associated polaritons can propagate over tens of unit cells in the plasmonic crystal [12]. The relevance of SLRs for enhanced, directional, and polarized light emission [11,14] and sensing [15] has been recently demonstrated. Although the coupling of surface modes in periodic metallic structures has attracted much interest [16][17][18][19], especially for its connection with frequency stop gaps [20], coupled SLRs have not yet been discussed.In this paper, we demonstrate the mutual coupling of SLRs and the formation of a frequency stop gap in the dispersion ...

Periodic arrays of metallic nanoparticles may sustain Surface Lattice Resonances (SLRs), which are collective resonances associated with the diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By investigating a series of arrays with varying number of particles, we traced the evolution of SLRs to its origins. Polarization resolved extinction spectra of arrays formed by a few nanoparticles were measured, and found to be in very good agreement with calculations based on a coupled dipole model. Finite size effects on the optical properties of the arrays are observed, and our results provide insight into the characteristic length scales for collective plasmonic effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than 20 x 20 particles, the Q-factors of SLRs saturate at a much larger value than those of LSPRs; in between, the Q-factors of SLRs are an increasing function of the number of particles in the array.Comment: 4 figure

We present indications of thermalization and cooling of quasiparticles, a precursor for quantum condensation, in a plasmonic nanoparticle array. We investigate a periodic array of metallic nanorods covered by a polymer layer doped with an organic dye at room temperature. Surface lattice resonances of the array--hybridized plasmonic-photonic modes--couple strongly to excitons in the dye, and bosonic quasiparticles which we call plasmon-exciton polaritons (PEPs) are formed. By increasing the PEP density through optical pumping, we observe thermalization and cooling of the strongly coupled PEP band in the light emission dispersion diagram. For increased pumping, we observe saturation of the strong coupling and emission in a new weakly coupled band, which again shows signatures of thermalization and cooling.

Light-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light–matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination.