On the excitation and radiative decay rates of plasmonic nanoantennas

Quantum Dynamics of Plasmonic Coupling in Silver Nanoparticle Dimers: Enhanced Energy and Population Transfer via Emitter Interaction

Plasmonic nanoparticles (NPs), characterized by significant localized surface plasmon excitations, can generate exceptionally large electromagnetic fields. In the plasmonic cavity, the enhancement of population and energy transfer across closely spaced metallic NPs significantly influence the optical response of the emitter. The theoretical investigation of transport properties in plasmonic nanocavities in atomic-scale level of calculation is important to characterize the optical response of the system. We model the coupling of plasmonic excitations of silver NPs in a bowtie configuration and generate new bright and dark states according to symmetry. By varying the separation distance, the rate of population and energy transfer between two NPs are analyzed within the framework of quantum dynamics multiconfiguration time-dependent Hartree (MCTDH) algorithm. The coupling of the emitter with bright and dark states of the plasmonic cavity is investigated based on the dipole-dipole approximation. The Hermitian Hamiltonian parametrized with first-principles calculations is applied to model the whole system. These results can reveal a connection between atomistic properties and optical response in the subnanometric-scale.

Nanocavities for Molecular Optomechanics: Their Fundamental Description and Applications

Vibrational Raman scattering-a process where light exchanges energy with a molecular vibration through inelastic scattering-is most fundamentally described in a quantum framework where both light and vibration are quantized. When the Raman scatterer is embedded inside a plasmonic nanocavity, as in some sufficiently controlled implementations of surface-enhanced Raman scattering (SERS), the coupled system realizes an optomechanical cavity where coherent and parametrically amplified light-vibration interaction becomes a resource for vibrational state engineering and nanoscale nonlinear optics. The purpose of this Perspective is to clarify the connection between the languages and parameters used in the fields of molecular cavity optomechanics (McOM) versus its conventional, "macroscopic" counterpart and to summarize the main results achieved so far in McOM and the most pressing experimental and theoretical challenges. We aim to make the theoretical framework of molecular cavity optomechanics practically usable for the SERS and nanoplasmonics community at large. While quality factors (Q) and mode volumes (V) essentially describe the performance of a nanocavity in enhancing light-matter interaction, we point to the light-cavity coupling efficiencies (η) and optomechanical cooperativities () as the key parameters for molecular optomechanics. As an illustration of the significance of these quantities, we investigate the feasibility of observing optomechanically induced transparency with a molecular vibration-a measurement that would allow for a direct estimate of the optomechanical cooperativity.

Plasmon-enhanced multi-photon excited photoluminescence of Au, Ag, and Pt nanoclusters

In this work, we have studied the multi-photon excited photoluminescence from metal nanoclusters (NCs) of Au, Ag and Pt embedded in Al2O3matrix by ion implantation. The thermal annealing process allows to obtain a system composed of larger plasmonic metal nanoparticles (NPs) surrounded by photoluminescent ultra-small metal NCs. By exciting at 1064 nm, visible emission, ranging from 450 to 800 nm, was detected. The second and fourth-order nature of the multiphoton process was verified in a power-dependent study measured for each sample below the damage threshold. Experiments show that Au and Ag NCs exhibit a four-fold enhanced multiphoton excited photoluminescence with respect to that observed for Pt NCs, which can be explained as a result of a plasmon-mediated near-field process that is of less intensity for Pt NPs. These findings provide new opportunities to combine plasmonic nanoparticles and photoluminescent nanoclusters inside a robust inorganic matrix to improve their optical properties. Plasmon-enhanced multiphoton excited photoluminescence from metal nanoclusters may find potential application as ultrasmall fluorophores in multiphoton sensing, and in the development of solar cells with highly efficient energy conversion modules.

Recent Advances in Tunable Metasurfaces: Materials, Design, and Applications

Metasurfaces, a two-dimensional (2D) form of metamaterials constituted by planar meta-atoms, exhibit exotic abilities to tailor electromagnetic (EM) waves freely. Over the past decade, tremendous efforts have been made to develop various active materials and incorporate them into functional devices for practical applications, pushing the research of tunable metasurfaces to the forefront of nanophotonics. Those active materials include phase change materials (PCMs), semiconductors, transparent conducting oxides (TCOs), ferroelectrics, liquid crystals (LCs), atomically thin material, etc., and enable intriguing performances such as fast switching speed, large modulation depth, ultracompactness, and significant contrast of optical properties under external stimuli. Integration of such materials offers substantial tunability to the conventional passive nanophotonic platforms. Tunable metasurfaces with multifunctionalities triggered by various external stimuli bring in rich degrees of freedom in terms of material choices and device designs to dynamically manipulate and control EM waves on demand. This field has recently flourished with the burgeoning development of physics and design methodologies, particularly those assisted by the emerging machine learning (ML) algorithms. This review outlines recent advances in tunable metasurfaces in terms of the active materials and tuning mechanisms, design methodologies, and practical applications. We conclude this review paper by providing future perspectives in this vibrant and fast-growing research field.