S. R. K. Rodriguez

Coupling Bright and Dark Plasmonic Lattice Resonances

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 high-frequency 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.

Hybrid plasmonic-photonic modes in diffractive arrays of nanoparticles coupled to light-emitting optical waveguides

We study the hybridized plasmonic-photonic modes supported by two-dimensional arrays of metallic nanoparticles coupled to light-emitting optical waveguides. Localized surface plasmon polaritons in the metallic nanoparticles can couple to guided modes in the underlying waveguide, forming quasi-guided hybrid modes, or to diffracted orders in the plane of the array, forming surface lattice resonances. We consider three kinds of samples: one sustains quasi-guided modes only, another sustains surface lattice resonances only, and a third sample sustains both modes. This third sample constitutes the first demonstration of simultaneous coupling of localized surface plasmons to guided modes and diffracted orders. The dispersive properties of the modes in the samples are investigated through light extinction and emission spectroscopy. We elucidate the conditions that lead to the coexistence of surface lattice resonances and quasi-guided hybrid modes, and assess their potential for enhancing the luminescence of emitters embedded in the coupled waveguide. We find the largest increase in emission intensity for the surface lattice resonances, reaching up to a factor of 20.

Collective resonances in plasmonic crystals : size matters

Abstract Periodic arrays of metallic nanoparticles may sustain surface lattice resonances (SLRs), which are collective resonances associated with the diffractive coupling of localized surface plasmons 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 × 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than ∼ 20 × 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.

Surface lattice resonances strongly coupled to Rhodamine 6G excitons : tuning the plasmon-exciton-polariton mass and composition

We demonstrate the strong coupling of surface lattice resonances (SLRs)--hybridized plasmonic/photonic modes in metallic nanoparticle arrays--to excitons in Rhodamine 6G molecules. We investigate experimentally angle-dependent extinction spectra of silver nanorod arrays with different lattice constants, with and without the Rhodamine 6G molecules. The properties of the coupled modes are elucidated with simple Hamiltonian models. At low momenta, plasmon-exciton-polaritons--the mixed SLR/exciton states--behave as free-quasiparticles with an effective mass, lifetime, and composition tunable via the periodicity of the array. The results are relevant for the design of plasmonic systems aimed at reaching the quantum degeneracy threshold, wherein a single quantum state becomes macroscopically populated.

Nanoscale Spatial Coherent Control over the Modal Excitation of a Coupled Plasmonic Resonator System

We demonstrate coherent control over the optical response of a coupled plasmonic resonator by high-energy electron beam excitation. We spatially control the position of an electron beam on a gold dolmen and record the cathodoluminescence and electron energy loss spectra. By selective coherent excitation of the dolmen elements in the near field, we are able to manipulate modal amplitudes of bonding and antibonding eigenmodes. We employ a combination of CL and EELS to gain detailed insight in the power dissipation of these modes at the nanoscale as CL selectively probes the radiative response and EELS probes the combined effect of Ohmic dissipation and radiation.

Probing a Dissipative Phase Transition via Dynamical Optical Hysteresis

We experimentally explore the dynamical 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 influence of fluctuations, which trigger 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 for a single mode resonator influenced by quantum fluctuations, and the present experimental approach is promising for exploring critical phenomena in photonic lattices.

Interaction-induced hopping phase in driven-dissipative coupled photonic microcavities

The Bose-Hubbard model (BHM) describes bosons hopping across sites and interacting on-site. Inspired by the success of BHM simulators with atoms in optical lattices, proposals for implementing the BHM with photons in coupled nonlinear cavities have recently emerged. Two coupled semiconductor microcavities constitute a model system where the hopping, interaction and decay of exciton polaritons—mixed light-matter quasiparticles—can be engineered in combination with site-selective coherent driving to implement the driven-dissipative two-site optical BHM. Here we explore the interplay of interference and nonlinearity in this system, in a regime where three distinct density profiles can be observed under identical driving conditions. We demonstrate how the phase acquired by polaritons hopping between cavities can be controlled through polariton-polariton interactions. Our results open new perspectives for synthesizing density-dependent gauge fields using polaritons in two-dimensional multicavity systems.

Active Liquid Crystal Tuning of Metallic Nanoantenna Enhanced Light Emission from Colloidal Quantum Dots

A system comprising an aluminum nanoantenna array on top of a luminescent colloidal quantum dot waveguide and covered by a thermotropic liquid crystal (LC) is introduced. By heating the LC above its critical temperature, we demonstrate that the concomitant refractive index change modifies the hybrid plasmonic-photonic resonances in the system. This enables active control of the spectrum and directionality of the narrow-band (∼6 nm) enhancement of quantum dot photoluminescence by the metallic nanoantennas.

Classical and quantum distinctions between weak and strong coupling

Coupled systems subject to dissipation exhibit two different regimes known as weak coupling and strong coupling. Two damped coupled harmonic oscillators (CHOs) constitute a model system where the key features of weak and strong coupling can be identified. Several of these features are common to classical and quantum systems, as a number of quantum-classical correspondences have shown. However, the condition defining the boundary between weak and strong coupling is distinct in classical and quantum formalisms. Here we describe the origin of two widely used definitions of strong coupling. Using a classical CHO model, we show that energy exchange cycles and avoided resonance crossings signal the onset of strong coupling according to one criterion. From the classical CHO model we derive a non-Hermitian Hamiltonian describing open quantum systems. Based on the analytic properties of the Hamiltonian, we identify the boundary between weak and strong coupling with a different feature: a non-Hermitian degeneracy known as the exceptional point. For certain parameter ranges the classical and quantum criterion for strong coupling coincide; for other ranges they do not. Examples of systems in strong coupling according to one or another criterion, but not both, are illustrated. The framework here presented is suitable for introducing graduate or advanced undegraduate students to the basic properties of strongly coupled systems, as well as to the similarities and subtle differences between classical and quantum descriptions of coupled dissipative systems.

Directional sideward emission from luminescent plasmonic nanostructures

Periodic arrays of metallic nanoparticles can be used to enhance the emission of light in certain directions. We fabricated hexagonal arrays of aluminium nanoparticles combined with thin layers of luminescent material and optimized period (275 nm) and thickness (1500 nm) to obtain sideward directional emission into glass for a wavelength band around 620 nm. The key physics is that the luminescent layer acts as a waveguide, from which light is emitted at preferential angles using diffractive effects. This phenomenon has applications in the field of solid-state lighting, where there is a desire for small, bright and directional sources.