Ten years of spasers and plasmonic nanolasers

Broadband Acoustic Purcell Effect from Collective Bound States in the Continuum

The Purcell effect significantly improves the performance of various emission devices but is typically constrained by a narrow operational bandwidth due to inherent resonant mechanisms. This study achieves broadband acoustic Purcell effect, substantially boosting sound emission by exploring collective quasibound states in the continuum (QBICs). A six-cavity coupled system supporting five QBICs is introduced, wherein all of the QBICs interact strongly with an acoustic source. This system takes advantage of the high quality factors and the strong mode responses of the collective QBICs, leading to a substantial enhancement of the local density of states. Consequently, a considerable increase in sound emission is realized across the frequency range of 625-900 Hz. These findings provide insights into the physical mechanisms driving the broadband Purcell effect in resonant systems and open up promising avenues for the development of advanced acoustic emission devices.

Controlling Raman enhancement in particle-aperture hybrid nanostructures by interlayer spacing

Here we show how surface-enhanced Raman spectroscopy (SERS) features can be fine-tuned in optically active substrates made of layered materials. To demonstrate this, we used DNA-assisted lithography (DALI) to create substrates with silver bowtie nanoparticle-aperture pairs and then coated the samples with rhodamine 6G (R6G) molecules. By varying the spacing between the aperture and particle layer, we were able to control the strength of the interlayer coupling between the plasmon resonances of the apertures and those of the underlying bowtie particles. The changes in the resulting field enhancements were confirmed by recording the Raman spectra of R6G from the substrates, and the experimental findings were supported with finite difference time domain (FDTD) simulations including reflection/extinction and near-field profiles.

Innovative Approach to Achieving Polarization Dependent Highly Directional Nanolasers Through Propagating States in Diverse Plasmonic Lattices

With their extremely small mode volumes, excellent field enhancement, and low radiative loss, metallic nanoparticle arrays supporting plasmonic lattice resonances have emerged as a potential design for on-chip plasmonic lasers. Due to the similarities between photonic crystals and plasmonic lattices in terms of structural features and energy band structure, the properties of plasmonic lattice-based nanolasers, including low threshold, lasing wavelength, coherence, directionality, and polarization, can be designed using band structure computations. Here 2D plasmonic lattices of Al nanocone arrays (NCAs) are presented, supporting narrow linewidth resonances that provide optical feedback for the stimulated emission process of optically pumped Rhodamine 6G (R6G). Remarkably, highly directional nanoscale lasing with polarization dependence at red-light wavelengths is presented by the artificially predesigned plasmonic band structure at the propagating state with different lattice symmetries and enables effective coupling with quantum emitters at various wavelengths. Furthermore, the lasing dynamics in these structures are also investigated, employing a dynamic semi-quantum approach that considers both stimulated and spontaneous emission. These findings broaden the lasing characteristics diversity in plasmonic nanoparticle arrays and provide a simple framework for presenting promising prospects for the management and operation of on-chip nanoscale laser sources.

High-refractive-index 2D photonic structures for robust low-threshold multiband lasing

High-refractive-index (HRI) dielectrics are gaining increasing attention as building blocks for compact lasers. Their ability to simultaneously support both electric and magnetic modes provides greater versatility as compared to plasmonic platforms. Moreover, their reduced absorption loss minimizes heat generation, further enhancing their performance. Here, we employ a scalable soft nanoimprinting lithography method to create a series of two-dimensional (2D) periodic square hole arrays in polymeric films (SU-8), which are coated with an HRI dielectric layer (TiO2). These structures exhibit low-threshold lasing from an organic dye-doped SU-8 layer deposited on top. We study arrays with different lattice parameters and a sample with a random distribution of holes, finding that the optimal laser performance occurs when the optical resonances of the array align with the emission wavelength range of the dye. Furthermore, we observe that the anisotropy in the TiO2 coating breaks the polarization degeneracy of the square arrays, leading to the emergence of new modes and enabling the simultaneous appearance of multiple lasing peaks. Our work shows that, despite the simplicity of their fabrication process, the HRI structures studied here exhibit a high degree of complexity, leading to a rich optical response and enabling multiband lasing. This offers an innovative approach to building robust HRI platforms for lasing with improved control over their emission properties.

Ten Years of Perovskite Lasers

Over the past decade, semiconducting halide perovskite lasers have emerged as a transformative platform in optoelectronics, owing to unique properties such as high photoluminescence quantum yields, tunable bandgaps, and low-cost fabrication processes. This review systematically examines the advancements in halide perovskite lasers, covering diverse laser architectures, such as whispering gallery mode, Fabry-Pérot, plasmonic, bound states in the continuum (BIC), quantum dot, and polariton lasers. The mechanisms of optical gain, the role of material engineering in optimizing lasing performance, and the challenges associated with continuous-wave (CW) pumping and electrically driven lasing are discussed. Furthermore, recent progress in improving the stability and scalability of perovskite lasers, essential for their integration into practical applications in displays, optical communications, sensing, and integrated photonics is highlighted. Finally, future research directions are discussed, emphasizing the potential of perovskite lasers to revolutionize various technological domains by enabling the development of next-generation photonic devices.

Half-wave nanolasers and intracellular plasmonic lasing particles

The ultimate limit for laser miniaturization would be achieving lasing action in the lowest-order cavity mode within a device volume of ≤(λ/2n)3, where λ is the free-space wavelength and n is the refractive index. Here we highlight the equivalence of localized surface plasmons and surface plasmon polaritons within resonant systems, introducing nanolasers that oscillate in the lowest-order localized surface plasmon or, equivalently, half-cycle surface plasmon polariton. These diffraction-limited single-mode emitters, ranging in size from 170 to 280 nm, harness strong coupling between gold and InxGa1-xAs1-yPy in the near-infrared (λ = 1,000-1,460 nm), away from the surface plasmon frequency. This configuration supports only the lowest-order dipolar mode within the semiconductor's broad gain bandwidth. A quasi-continuous-level semiconductor laser model explains the lasing dynamics under optical pumping. In addition, we fabricate isolated gold-coated semiconductor discs and demonstrate higher-order lasing within live biological cells. These plasmonic nanolasers hold promise for multi-colour imaging and optical barcoding in cellular applications.

Boosting Light-Matter Interactions in Plasmonic Nanogaps

Plasmonic nanogaps in strongly coupled metal nanostructures can confine light to nanoscale regions, leading to huge electric field enhancement. This unique capability makes plasmonic nanogaps powerful platforms for boosting light-matter interactions, thereby enabling the rapid development of novel phenomena and applications. This review traces the progress of nanogap systems characterized by well-defined morphologies, controllable optical responses, and a focus on achieving extreme performance. The properties of plasmonic gap modes in far-field resonance and near-field enhancement are explored and a detailed comparative analysis of nanogap fabrication techniques down to sub-nanometer scales is provided, including bottom-up, top-down, and their combined approaches. Additionally, recent advancements and applications across various frontier research areas are highlighted, including surface-enhanced spectroscopy, plasmon-exciton strong coupling, nonlinear optics, optoelectronic devices, and other applications beyond photonics. Finally, the challenges and promising emerging directions in the field are discussed, such as light-driven atomic effects, molecular optomechanics, and alternative new materials.

Plasmonic Hinge Modes in Metal-Coated Nanolasers

Plasmonic lasers have traditionally been built on flat metal substrates. Here, we introduce substrate-free plasmonic lasers created by coating semiconductor particles with an optically thin layer of noble metal. This architecture supports plasmonic "hinge" modes highly localized along the particle's edges and corners, exhibiting Purcell factors exceeding 100 and Q-factors of 15-20 near the plasmon resonance frequency. We demonstrate hinge-mode lasing in submicron CsPbBr3 perovskite cubes encapsulated with conformal 15-nm-thick gold shells. The lasing is achieved with 480-nm nanosecond pumping at 10 pJ/μm2 through the translucent gold layer, producing a line width of 0.6 at 538 nm. Their rapidly decaying evanescent fields outside the gold coating show distinct sensitivities to long- and short-range external perturbations. Our results suggest the potential of these novel laser modes for sensing and imaging applications.

Thresholdless coherence in a superradiant laser

Lasing threshold in the conventional lasers is the minimum input power required to initiate laser oscillation. It has been widely accepted that the conventional laser threshold occurring around a unity intracavity photon number can be eliminated in the input-output curve by making the so-called β parameter approach unity. The recent experiments, however, have revealed that even in this case the photon statistics still undergo a transition from coherent to thermal statistics when the intracavity mean photon number is decreased below unity. Since the coherent output is only available above the diminished threshold, the long-sought promise of thresholdless lasers to produce always coherent light has become questionable. Here, we present an always-coherent thresholdless laser based on superradiance by two-level atoms in a quantum superposition state with the same phase traversing a high-Q cavity. Superradiant lasing was observed without the conventional lasing threshold around the unity photon number and the photon statistics remained near coherent even below it. The coherence was improved by reducing the coupling constant as well as the excited-state amplitude in the superposition state. Our results pave a way toward always-coherent thresholdless lasers with more practical media such as quantum dots, nitrogen-vacancy centers and doped ions in crystals.

Microstructure-Assisted Wafer-Scale Fabrication of Perovskite Microlaser Arrays

All inorganic lead halide perovskites exhibit fascinating optical and optoelectronic characteristics for on-chip lasing, but the lack of precise control of wafer-scale fabrication for perovskite microstructure arrays restricts their potential applications in on-chip-integrated devices. In this work, a microstructure-template assisted crystallization method is demonstrated via a designed chemical vapor deposition process, achieving the controllable fabrication of homogeneous perovskite micro-hemispheroid (PeMH) arrays spanning the entire surface area of a 4-inch wafer. Benefiting from the low-loss whispering gallery resonance and plasmon-enhanced light-matter interactions in well-confined hybrid cavities, this CsPbX3/Ag (X = Cl, Br) plasmonic microlasers exhibit quite low thresholds below 10 µJ cm-2. Interestingly, these thresholds can be efficiently modulated through the manipulation of plasmonic resonance and electromagnetic field mode in PeMHs owning various diameters. This strategy not only provides a valuable methodology for the large-scale fabrication of perovskite microstructures but also endorses the potential of all-inorganic perovskite nanostructures as promising candidates for on-chip-integrated light sources.

Strongly coupled plasmon-exciton polaritons for photobleaching suppression

Strong light-matter interactions have received a lot of attention, for example in the pursuit of plasmonic-excitonic structures as coherent light sources with low-power threshold. In this study, we investigate the influence of room temperature strong coupling between surface plasmon polaritons (SPP) and excitons on fluorescence lifetimes and photobleaching effects. Our plasmonic-photonic structure, comprising of thin silver (Ag) and gold (Au) layers with a Rhodamine 6G (R6G) dye layer, shows a clear shift in the plasmon resonance and R6G absorption lines with varying incident angles, indicative of strong coupling, with a measured Rabi splitting of approximately 90 meV. Fluorescence lifetime imaging microscopy (FLIM) was then employed to assess photobleaching, revealing a significant reduction in photobleaching effect for in strongly coupled plasmonic-excitonic structures compared to single Rhodamine R6G layers. Our findings indicate the pivotal role of strong light-matter interactions in reducing photobleaching effects and stabilizing fluorescence intensities, offering promising avenues for developing quantum multiparticle nanophotonic devices with enhanced stability and performance.

Singular dielectric nanolaser with atomic-scale field localization

Compressing the optical field to the atomic scale opens up possibilities for directly observing individual molecules, offering innovative imaging and research tools for both physical and life sciences. However, the diffraction limit imposes a fundamental constraint on how much the optical field can be compressed, based on the achievable photon momentum1,2. In contrast to dielectric structures, plasmonics offer superior field confinement by coupling the light field with the oscillations of free electrons in metals3-6. Nevertheless, plasmonics suffer from inherent ohmic loss, leading to heat generation, increased power consumption and limitations on the coherence time of plasmonic devices7,8. Here we propose and demonstrate singular dielectric nanolasers showing a mode volume that breaks the optical diffraction limit. Derived from Maxwell's equations, we discover that the electric-field singularity sustained in a dielectric bowtie nanoantenna originates from divergence of momentum. The singular dielectric nanolaser is constructed by integrating a dielectric bowtie nanoantenna into the centre of a twisted lattice nanocavity. The synergistic integration surpasses the diffraction limit, enabling the singular dielectric nanolaser to achieve an ultrasmall mode volume of about 0.0005 λ3 (λ, free-space wavelength), along with an exceptionally small feature size at the 1-nanometre scale. To fabricate the required dielectric bowtie nanoantenna with a single-nanometre gap, we develop a two-step process involving etching and atomic deposition. Our research showcases the ability to achieve atomic-scale field localization in laser devices, paving the way for ultra-precise measurements, super-resolution imaging, ultra-efficient computing and communication, and the exploration of light-matter interactions within the realm of extreme optical field localization.

High-Power Impulse Magnetron Sputter Deposition of Ag on Self-Assembled Au Nanoparticle Arrays at Low-Temperature Dewetting Conditions

Plasmons have facilitated diverse analytical applications due to the boosting signal detectability by hot spots. In practical applications, it is crucial to fabricate straightforward, large-scale, and reproducible plasmonic substrates. Dewetting treatment, via applying direct thermal annealing of metal films, has been used as a straightforward method in the fabrication of such plasmonic nanostructures. However, tailoring the evolution of the dewetting process of metal films poses considerable experimental complexities, mainly due to nanoscale structure formation. Here, we use grazing-incidence small- and wide-angle X-ray scattering for the in situ investigation of the high-power impulse magnetron sputter deposition of Ag on self-assembled Au nanoparticle arrays at low-temperature dewetting conditions. This approach allows us to examine both the direct formation of binary Au/Ag nanostructure and the consequential impact of the dewetting process on the spatial arrangement of the bimetallic nanoparticles. It is observed that the dewetting at 100 °C is sufficient to favor the establishment of a homogenized structural configuration of bimetallic nanostructures, which is beneficial for localized surface plasmon resonances (LSPRs). The fabricated metal nanostructures show potential application for the surface-enhanced Raman scattering (SERS) detection of rhodamine 6G molecules. As SERS platform, bimetallic nanostructures formed with dewetting conditions turn out to be superior to those without dewetting conditions. The method in this work is envisioned as a facile strategy for the fabrication of plasmonic nanostructures.

Nanolasers: More than a decade of progress, developments and challenges

As the demand for smaller and more compact lasers increases, the physical dimensions of laser diodes are already at the diffraction limit, which impairs this miniaturization trend and limits direct laser integration into photonic and especially nanophotonic circuits. However, plasmonics has allowed the development of a novel class of lasers that can be manufactured without being limited by diffraction, exhibiting ultralow energy consumption, small volumes, and high modulation speeds that could someday compete with their modern macroscale counterparts. Nevertheless, a wide variety of issues create roadblocks for further development and commercial adoption. Here we conduct a monolithic review in which we formulate the definition of a nanolaser, categorize nanolasers, and examine their properties and applications to determine if nanolasers do present a potential technological revolution as they seem to exhibit or are too restricted by the issues that plague them to ever succeed.

Design of an ultrafast plasmonic nanolaser for high-intensity broadband emission operating at room temperature

We propose a plasmonic nanolaser based on a metal-insulator-semiconductor-insulator-metal (MISIM) structure, which effectively confines light on a subwavelength scale (∼λ/14). As the pump power increases, the proposed plasmonic nanolaser exhibits broadband output characteristics of 20 nm, and the maximum output power can reach 20 µW. Furthermore, the carrier lifetime at the upper energy level in our proposed structure is measured to be about 400 fs using a double pump-probe excitation. The ultrafast characteristic is attributed to the inherent Purcell effect of plasmonic systems. Our work paves the way toward deep-subwavelength mode confinement and ultrafast femtosecond plasmonic lasers in spaser-based interconnected, eigenmode engineering of plasmonic nanolasers, nano-LEDs, and spontaneous emission control.

Self-Competitive Growth of CsPbBr3 Planar Nanowire Array

Semiconductor planar nanowire arrays (PNAs) are essential for achieving large-scale device integration. Direct heteroepitaxy of PNAs on a flat substrate is constrained by the mismatch in crystalline symmetry and lattice parameters between the substrate and epitaxial nanowires. This study presents a novel approach termed "self-competitive growth" for heteroepitaxy of CsPbBr3 PNAs on mica. The key to inducing the self-competitive growth of CsPbBr3 PNAs on mica involves restricting the nucleation of CsPbBr3 nanowires in a high-adsorption region, which is accomplished by overlaying graphite sheets on the mica surface. Theoretical calculations and experimental results demonstrate that CsPbBr3 nanowires oriented perpendicular to the boundary of the high-adsorption area exhibit greater competitiveness in intercepting the growth of nanowires in the other two directions, resulting in PNAs with a consistent orientation. Moreover, these PNAs exhibit low-threshold and stable amplified spontaneous emission under one-, two-, and three-photon excitation, indicating their potential for an integrated laser array.

Circular quantum wire symmetrically loaded with a graphene strip as the plasmonic micro/nano laser: threshold conditions analysis

We study, apparently for the first time, the threshold conditions for the time-harmonic natural modes of the micro-to-nanosize plasmonic laser shaped as a circular quantum wire with a flat graphene strip, placed symmetrically inside it, in the H-polarization case. We suppose that the quantum wire is made of a nonmagnetic gain material, characterized with the aid of the "active" imaginary part of the complex refractive index. The emergence of lasers integrating plasmonic effects marks a significant trend in contemporary photonics. Here, the graphene offers a promising alternative to the noble metals as it exhibits the capacity to sustain plasmon-polariton natural surface waves across the infrared and terahertz (THz) spectra. The used innovative approach is the lasing eigenvalue problem (LEP), which is classical electromagnetic field boundary-value problem, adapted to the presence of active region. It is tailored to deliver both the mode-specific emission frequency, which is purely real at the threshold, and the value of the gain index of the active region, necessary to make the frequency real-valued. The conductivity of graphene is characterized using the quantum Kubo formalism. We reduce the LEP for the considered nanolaser to a hyper-singular integral equation for the current on the strip and discretize it by the Nystrom-type method. This method is meshless and computationally economic. After discretization, a matrix equation is obtained. The sought for mode-specific pairs {the frequency and the threshold gain index} correspond to the zeros of the matrix determinant. It should be noted that the convergence to exact LEP eigenvalues is guaranteed mathematically if the discretization order is taken progressively larger. Two families of modes are identified and studied: the modes of the quantum wire, perturbed by the presence of the graphene strip and the plasmon modes of the strip. The frequencies of all plasmon modes and the lowest mode of the quantum wire are found to be well-tuned by changing the chemical potential of graphene. Engineering analytic formulas for the plasmon-mode frequencies and thresholds are derived. We believe that the presented results can be used in the creation of single-mode tunable micro and nanolasers.

Orientational effects in the polarized absorption spectra of molecular aggregates

We present a detailed theoretical analysis of polarized absorption spectra and linear dichroism of cyanine dye aggregates whose unit cells contain two molecules. The studied threadlike ordered system with a molecular exciton delocalized along its axis can be treated as two chains of conventional molecular aggregates, rotated relative to each other at a certain angle around the aggregate axis. Our approach is based on the general formulas for the effective cross section of light absorption by a molecular aggregate and key points of the molecular exciton theory. We have developed a self-consistent theory for describing the orientational effects in the absorption and dichroic spectra of such supramolecular structures with nonplanar unit cell. It is shown that the spectral behavior of such systems exhibits considerable distinctions from that of conventional cyanine dye aggregates. They consist in the strong dependence of the relative intensities of the J- and H-type spectral bands of the aggregate with a nonplanar unit cell on the angles determining the mutual orientations of the transition dipole moments of constituting molecules and the aggregate axis as well as on the polarization direction of incident light. The derived formulas are reduced to the well-known analytical expressions in the particular case of aggregates with one molecule in the unit cell. The calculations performed within the framework of our excitonic theory combined with available vibronic theory allow us to quite reasonably explain the experimental data for the pseudoisocyanine bromide dye aggregate.

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing.

On-Chip Monolithically Integrated Ultraviolet Low-Threshold Plasmonic Metal-Semiconductor Heterojunction Nanolasers

The metal-semiconductor heterojunction is imperative for the realization of electrically driven nanolasers for chip-level platforms. Progress in developing such nanolasers has hitherto rarely been realized, however, because of their complexity in heterojunction fabrication and the need to use noble metals that are incompatible with microelectronic manufacturing. Most plasmonic nanolasers lase either above a high threshold (101 -103  MW cm-2 ) or at a cryogenic temperature, and lasing is possible only after they are removed from the substrate to avoid the large ohmic loss and the low modal reflectivity, making monolithic fabrication impossible. Here, for the first time, record-low-threshold, room-temperature ultraviolet (UV) lasing of plasmon-coupled core-shell nanowires that are directly grown on silicon is demonstrated. The naturally formed core-shell metal-semiconductor heterostructure of the nanowires leads to a 100-fold improvement in growth density over previous results. This unprecedentedly high nanowire density creates intense plasmonic resonance, which is outcoupled to the resonant Fabry-Pérot microcavity. By boosting the emission strength by a factor of 100, the hybrid photonic-plasmonic system successfully facilitates a record-low laser threshold of 12 kW cm-2 with a spontaneous emission coupling factor as high as ≈0.32 in the 340-360 nm range. Such architecture is simple and cost-competitive for future UV sources in silicon integration.

GST plasmonic gap structure investigation as a switch and sensor

In this paper, a plasmonic perfect absorber that consists of a gold rectangular bar with three gaps is investigated as a switch and sensor in the near-infrared region. Phase change material germanium-antimony-tellurium (GST) is utilized in two gaps to perform the switching capability with a high extinction ratio of 18.49 dB. In addition, the sensing performance of the structure for detection of a solution of glucose in water and diagnosis of different cancer cells is studied. The best sensitivity of 1504 nm/RIU is obtained for detection of the PC12 cancer cell, and the figure of merit of the structure is around 17R I U -1.

Chemical and Physical Properties of Photonic Noble-Metal Nanomaterials

Colloidal noble metal nanoparticles (NPs) are composed of metal cores and organic or inorganic ligand shells. These NPs support size- and shape-dependent plasmonic resonances. They can be assembled from dispersions into artificial metamolecules which have collective plasmonic resonances originating from coupled bright and dark optical electric and magnetic modes that form depending on the size and shape of the constituent NPs and their number, arrangement, and interparticle distance. NPs can also be assembled into extended 2D and 3D metamaterials that are glassy thin films or ordered thin films or crystals, also known as superlattices and supercrystals. The metamaterials have tunable optical properties that depend on the size, shape, and composition of the NPs, and on the number of NP layers and their interparticle distance. Interestingly, strong light-matter interactions in superlattices form plasmon polaritons. Tunable interparticle distances allow designer materials with dielectric functions tailorable from that characteristic of an insulator to that of a metal, and serve as strong optical absorbers or scatterers, respectively. In combination with lithography techniques, these extended assemblies can be patterned to create subwavelength NP superstructures and form large-area 2D and 3D metamaterials that manipulate the amplitude, phase, and polarization of transmitted or reflected light.

Plexcitonics: plasmon-exciton coupling for enhancing spectroscopy, optical chirality, and nonlinearity

Plexcitonics is a rapidly developing interdisciplinary field that holds immense potential for the creation of innovative optical technologies and devices. This field focuses on investigating the interactions between plasmons and excitons in hybrid systems. In this review, we provide an overview of the fundamental principles of plasmonics and plexcitonics and discuss the latest advancements in plexcitonics. Specifically, we highlight the ability to manipulate plasmon-exciton interactions, the emerging field of tip-enhanced spectroscopy, and advancements in optical chirality and nonlinearity. These recent developments have spurred further research in the field of plexcitonics and offer inspiration for the design of advanced materials and devices with enhanced optical properties and functionalities.

Intrinsic Optical Properties and Emerging Applications of Gold Nanostructures

The collective oscillation of free electrons at the nanoscale surface of gold nanostructures is closely modulated by tuning the size, shape/morphology, phase, composition, hybridization, assembly, and nanopatterning, along with the surroundings of the plasmonic surface located at a dielectric interface with air, liquid, and solid. This review first introduces the physical origin of the intrinsic optical properties of gold nanostructures and further summarizes stimuli-responsive changes in optical properties, metal-field-enhanced optical signals, luminescence spectral shaping, chiroptical response, and photogenerated hot carriers. The current success in the landscape of nanoscience and nanotechnology mainly originates from the abundant optical properties of gold nanostructures in the thermodynamically stable face-centered cubic (fcc) phase. It has been further extended by crystal phase engineering to prepare thermodynamically unfavorable phases (e.g., kinetically stable) and heterophases to modulate their intriguing phase-dependent optical properties. A broad range of promising applications, including but not limited to full-color displays, solar energy harvesting, photochemical reactions, optical sensing, and microscopic/biomedical imaging, have fostered parallel research on the multitude of physical effects occurring in gold nanostructures.

Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications

Optical microbarcodes have recently received a great deal of interest because of their suitability for a wide range of applications, such as multiplexed assays, cell tagging and tracking, anticounterfeiting, and product labeling. Spectral barcodes are especially promising because they are robust and have a simple readout. In addition, microcavity- and microlaser-based barcodes have very narrow spectra and therefore have the potential to generate millions of unique barcodes. This review begins with a discussion of the different types of barcodes and then focuses specifically on microcavity-based barcodes. While almost any kind of optical microcavity can be used for barcoding, currently whispering-gallery microcavities (in the form of spheres and disks), nanowire lasers, Fabry-Pérot lasers, random lasers, and distributed feedback lasers are the most frequently employed for this purpose. In microcavity-based barcodes, the information is encoded in various ways in the properties of the emitted light, most frequently in the spectrum. The barcode is dependent on the properties of the microcavity, such as the size, shape, and the gain materials. Various applications of these barcodes, including cell tracking, anticounterfeiting, and product labeling are described. Finally, the future prospects for microcavity- and microlaser-based barcodes are discussed.

Highly Localized Surface Plasmon Nanolasers via Strong Coupling

Surface plasmons have robust and strong confinement to the light field which is beneficial for the light-matter interaction. Surface plasmon amplification by stimulated emission of radiation (SPACER) has the potential to be integrated on the semiconductor chip as a compact coherent light source, which can play an important role in further extension of Moore's law. In this study, we demonstrate the localized surface plasmon lasing at room temperature in the communication band using metallic nanoholes as the plasmonic nanocavity and InP nanowires as the gain medium. Optimizing laser performance has been demonstrated by coupling between two metallic nanoholes which adds another degree of freedom for manipulating the lasing properties. Our plasmonic nanolasers exhibit lower power consumption, smaller mode volumes, and higher spontaneous emission coupling factors due to enhanced light-matter interactions, which are very promising in the applications of high-density sensing and photonic integrated circuits.

On-chip integrated exceptional surface microlaser

The on-chip integrated visible microlaser is a core unit of high-speed visible-light communication with huge bandwidth resources, which needs robustness against fabrication errors, compressible linewidth, reducible threshold, and in-plane emission. However, until now, it has been a great challenge to meet these requirements simultaneously. Here, we report a scalable strategy to realize a robust on-chip integrated visible microlaser with further improved lasing performances enabled by the increased orders (n) of exceptional surfaces, and experimentally verify the strategy by demonstrating the performances of a second-order exceptional surface-tailored microlaser. We further prove the potential application of the strategy by discussing an exceptional surface-tailored topological microlaser with unique performances. This work lays a foundation for further development of on-chip integrated high-speed visible-light communication and processing systems, provides a platform for the fundamental study of non-Hermitian photonics, and proposes a feasible method of joint research for non-Hermitian photonics with nonlinear optics and topological photonics.

Perovskite Microlaser Integration with Metasurface Supporting Topological Waveguiding

Halide perovskite nano- and microlasers have become a very convenient tool for many applications from sensing to reconfigurable optical chips. Indeed, they exhibit outstanding emission robustness to crystalline defects due to so-called "defect tolerance" allowing for their simple chemical synthesis and further integration with various photonic designs. Here we demonstrate that such robust microlasers can be combined with another class of resilient photonic components, namely, with topological metasurfaces supporting topological guided boundary modes. We show that this approach allows to outcouple and deliver the generated coherent light over tens of microns despite the presence of defects of different nature in the structure: sharp corners in the waveguide, random location of the microlaser, and defects in the microlaser caused by mechanical pressure applied during its transfer to the metasurface. As a result, the developed platform provides a strategy to attain robust integrated lasing-waveguiding designs resilient to a broad range of structural imperfections, both for electrons in a laser and for pseudo-spin-polarized photons in a waveguide.

Dynamic Multi-Mode Mie Model for Gain-Assisted Metal Nano-Spheres

Coupling externally pumped gain materials with plasmonic spherical particles, even in the simplest case of a single spherical nanoparticle in a uniform gain medium, generates an incredibly rich variety of electrodynamic phenomena. The appropriate theoretical description of these systems is dictated by the quantity of the included gain and the size of the nano-particle. On the one hand, when the gain level is below the threshold separating the absorption and the emission regime, a steady-state approach is a rather adequate depiction, yet a time dynamic approach becomes fundamental when this threshold is exceeded. On the other hand, while a quasi-static approximation can be used to model nanoparticles when they are much smaller than the exciting wavelength, a more complete scattering theory is necessary to discuss larger nanoparticles. In this paper, we describe a novel method including a time-dynamical approach to the Mie scattering theory, which is able to account for all the most enticing aspects of the problem without any limitation in the particle's size. Ultimately, although the presented approach does not fully describe the emission regime yet, it does allow us to predict the transient states preceding emission and represents an essential step forward in the direction of a model able to adequately describe the full electromagnetic phenomenology of these systems.

Machine learning for nanoplasmonics

Plasmonic nanomaterials have outstanding optoelectronic properties potentially enabling the next generation of catalysts, sensors, lasers and photothermal devices. Owing to optical and electron techniques, modern nanoplasmonics research generates large datasets characterizing features across length scales. Furthermore, optimizing syntheses leading to specific nanostructures requires time-consuming multiparametric approaches. These complex datasets and trial-and-error practices make nanoplasmonics research ripe for the application of machine learning (ML) and advanced data processing methods. ML algorithms capture relationships between synthesis, structure and performance in a way that far exceeds conventional simulation and theory approaches, enabling effective performance optimization. For example, neural networks can tailor the nanostructure morphology to target desired properties, identify synthetic conditions and extract quantitative information from complex data. Here we discuss the nascent field of ML for nanoplasmonics, describe the opportunities and limitations of ML in nanoplasmonic research, and conclude that ML is potentially transformative, especially if the community curates and shares its big data.

Fluorescence decay enhancement and FRET inhibition in self-assembled hybrid gold CdSe/CdS/CdZnS colloidal nanocrystal supraparticles

We report on the synthesis of hybrid light emitting particles with a diameter ranging between 100 and 500 nm, consisting in a compact semiconductor CdSe/CdS/CdZnS nanocrystal aggregate encapsulated by a controlled nanometric size silica and gold layers. We first characterize the Purcell decay rate enhancement corresponding to the addition of the gold nanoshell as a function of the particle size and find a good agreement with the predictions of numerical simulations. Then, we show that the contribution corresponding to Förster resonance energy transfer is inhibited.

Lasing modes in ZnO nanowires coupled to planar metals

Semiconductor nanowire lasers can be subject to modifications of their lasing threshold resulting from a variation of their environment. A promising choice is to use metallic substrates to gain access to low-volume Surface-Plasmon-Polariton (SPP) modes. We introduce a simple, yet quantitatively precise model that can serve to describe mode competition in nanowire lasers on metallic substrates. We show that an aluminum substrate can decrease the lasing threshold for ZnO nanowire lasers while for a silver substrate, the threshold increases compared with a dielectric substrate. Generalizing from these findings, we make predictions describing the interaction between planar metals and semiconductor nanowires, which allow to guide future improvements of highly-integrated laser sources.

Sub-wavelength visualization of near-field scattering mode of plasmonic nano-cavity in the far-field

Spatial visualization of mode distribution of light scattering from plasmonic nanostructures is of vital importance for understanding the scattering mechanism and applications based on these plasmonic nanostructures. A long unanswered question in how the spatial information of scattered light from a single plasmonic nanostructure can be recovered in the far-field, under the constraints of the diffraction limit of the detection or imaging optical system. In this paper, we reported a theoretical model on retrieving local spatial information of scattered light by plasmonic nanostructures in a far-field optical imaging system. In the far-field parametric sin δ images, singularity points corresponding to near-field hot spots of the edge mode and the gap mode were resolved for gold ring and split rings with subwavelength diameters and feature sizes. The experimental results were verified with Finite Difference Time Domain (FDTD) simulation in the near-field and far-field, for the edge mode and the gap mode at 566 nm and 534 nm, respectively. In sin δ image of split-ring, two singularity points associated with near-field hot spots were visualized and resolved with the characteristic size of 90 and 100 nm, which is far below the diffraction limit. The reported results indicate the feasibility of characterizing the spatial distribution of scattering light in the far-field and with sub-wavelength resolution for single plasmonic nanostructures with sub-wavelength feature sizes.

Morphology-Controlled Reststrahlen Band and Infrared Plasmon Polariton in GaN Nanostructures

Due to ultrabright and stable blue light emission, GaN has emerged as one of the most famous semiconductors of the modern era, useful for light-emitting diodes, power electronics, and optoelectronic applications. Extending GaN's optical resonance from visible to mid- and-far-infrared spectral ranges will enable novel applications in many emerging technologies. Here we show hexagonal honeycomb-shaped GaN nanowall networks and vertically standing nanorods exhibiting morphology-dependent Reststrahlen band and plasmon polaritons that could be harnessed for infrared nanophotonics. Surface-induced dipoles at the edges and asperities in molecular beam epitaxy-deposited nanostructures lead to phonon absorption inside the Reststrahlen band, altering its shape from rectangular to right-trapezoidal. Excitation of such surface polariton modes provides a novel pathway to achieve far-infrared optical resonance in GaN. Additionally, surface defects in nanostructures lead to high carrier concentrations, resulting in tunable mid-infrared plasmon polaritons with high-quality factors. Demonstration of morphology-controlled Reststrahlen band and plasmon polaritons make GaN nanostructures attractive for infrared nanophotonics.

Plasmonic gain in current biased tilted Dirac nodes

Surface plasmons, which allow tight confinement of light, suffer from high intrinsic electronic losses. It has been shown that stimulated emission from excited electrons can transfer energy to plasmons and compensate for the high intrinsic losses. To-date, these realizations have relied on introducing an external gain media coupled to the surface plasmon. Here, we propose that plasmons in two-dimensional materials with closely located electron and hole Fermi pockets can be amplified, when an electrical current bias is applied along the displaced electron-hole pockets, without the need for an external gain media. As a prototypical example, we consider WTe₂ from the family of 1T[Formula: see text]-MX₂ materials, whose electronic structure can be described within a type-II tilted massive Dirac model. We find that the nonlocal plasmonic response experiences prominent gain for experimentally accessible currents on the order of mAμm^-1. Furthermore, the group velocity of the plasmon found from the isofrequency curves imply that the amplified plasmons are highly collimated along a direction perpendicular to the Dirac node tilt when the electrical current is applied along it.

Silver Nanoparticle Chains for Ultra-Long-Range Plasmonic Waveguides for Nd3+ Fluorescence

Plasmonic waveguides have been shown to be a promising approach to confine and transport electromagnetic energy beyond the diffraction limit. However, ohmic losses generally prevent their integration at micrometric or millimetric scales. Here, we present a gain-compensated plasmonic waveguide based on the integration of linear chains of Ag nanoparticles on an optically active Nd³⁺-doped solid-state gain medium. By means of dual confocal fluorescence microscopy, we demonstrate long-range optical energy propagation due to the near-field coupling between the plasmonic nanostructures and the Nd³⁺ ions. The subwavelength fluorescence guiding is monitored at distances of around 100 µm from the excitation source for two different emission ranges centered at around 900 nm and 1080 nm. In both cases, the guided fluorescence exhibits a strong polarization dependence, consistent with the polarization behavior of the plasmon resonance supported by the chain. The experimental results are interpreted through numerical simulations in quasi-infinite long chains, which corroborate the propagation features of the Ag nanoparticle chains at both excitation (λ_exc = 590 nm) and emission wavelengths. The obtained results exceed by an order of magnitude that of previous reports on electromagnetic energy transport using linear plasmonic chains. The work points out the potential of combining Ag nanoparticle chains with a small interparticle distance (~2 nm) with rare-earth-based optical gain media as ultra-long-range waveguides with extreme light confinement. The results offer new perspectives for the design of integrated hybrid plasmonic-photonic circuits based on rare-earth-activated solid-state platforms.

Near-unity Raman β-factor of surface-enhanced Raman scattering in a waveguide

The Raman scattering of light by molecular vibrations is a powerful technique to fingerprint molecules through their internal bonds and symmetries. Since Raman scattering is weak¹, methods to enhance, direct and harness it are highly desirable, and this has been achieved using optical cavities², waveguides^3-6 and surface-enhanced Raman scattering (SERS)^7-9. Although SERS offers dramatic enhancements^2,6,10,11 by localizing light within vanishingly small hot-spots in metallic nanostructures, these tiny interaction volumes are only sensitive to a few molecules, yielding weak signals¹². Here we show that SERS from 4-aminothiophenol molecules bonded to a plasmonic gap waveguide is directed into a single mode with >99% efficiency. Although sacrificing a confinement dimension, we find a SERS enhancement of ~10³ times across a broad spectral range enabled by the waveguide's larger sensing volume and non-resonant waveguide mode. Remarkably, this waveguide SERS is bright enough to image Raman transport across the waveguides, highlighting the role of nanofocusing^13-15 and the Purcell effect¹⁶. By analogy to the β-factor from laser physics^10,17-20, the near-unity Raman β-factor we observe exposes the SERS technique to alternative routes for controlling Raman scattering. The ability of waveguide SERS to direct Raman scattering is relevant to Raman sensors based on integrated photonics^7-9 with applications in gas sensing and biosensing.

Bio-Inspired Nanomembranes as Building Blocks for Nanophotonics, Plasmonics and Metamaterials

Nanomembranes are the most widespread building block of life, as they encompass cell and organelle walls. Their synthetic counterparts can be described as freestanding or free-floating structures thinner than 100 nm, down to monatomic/monomolecular thickness and with giant lateral aspect ratios. The structural confinement to quasi-2D sheets causes a multitude of unexpected and often counterintuitive properties. This has resulted in synthetic nanomembranes transiting from a mere scientific curiosity to a position where novel applications are emerging at an ever-accelerating pace. Among wide fields where their use has proven itself most fruitful are nano-optics and nanophotonics. However, the authors are unaware of a review covering the nanomembrane use in these important fields. Here, we present an attempt to survey the state of the art of nanomembranes in nanophotonics, including photonic crystals, plasmonics, metasurfaces, and nanoantennas, with an accent on some advancements that appeared within the last few years. Unlimited by the Nature toolbox, we can utilize a practically infinite number of available materials and methods and reach numerous properties not met in biological membranes. Thus, nanomembranes in nano-optics can be described as real metastructures, exceeding the known materials and opening pathways to a wide variety of novel functionalities.

Plasmonic nanolaser based on a single oligomer

We investigate the effect of manipulating the laser quality factor and the spectral properties of the gain medium on an oligomer-based plasmonic nanolaser. We develop different designs of the oligomer resonators, decreasing the lasing threshold and increasing the mode lifetime to improve the lasing efficiency. Based on the designs we are able to decrease the lasing threshold by a factor of ten. We discuss and show numerically the influence of the oligomer geometry, the lasing mode oscillation lifetime, and the photoluminescence peak linewidth of the gain medium on the lasing efficiency of the oligomer based plasmonic nanolaser.

Molecular Plasmonics with Metamaterials

Molecular plasmonics, the area which deals with the interactions between surface plasmons and molecules, has received enormous interest in fundamental research and found numerous technological applications. Plasmonic metamaterials, which offer rich opportunities to control the light intensity, field polarization, and local density of electromagnetic states on subwavelength scales, provide a versatile platform to enhance and tune light-molecule interactions. A variety of applications, including spontaneous emission enhancement, optical modulation, optical sensing, and photoactuated nanochemistry, have been reported by exploiting molecular interactions with plasmonic metamaterials. In this paper, we provide a comprehensive overview of the developments of molecular plasmonics with metamaterials. After a brief introduction to the optical properties of plasmonic metamaterials and relevant fabrication approaches, we discuss light-molecule interactions in plasmonic metamaterials in both weak and strong coupling regimes. We then highlight the exploitation of molecules in metamaterials for applications ranging from emission control and optical modulation to optical sensing. The role of hot carriers generated in metamaterials for nanochemistry is also discussed. Perspectives on the future development of molecular plasmonics with metamaterials conclude the review. The use of molecules in combination with designer metamaterials provides a rich playground both to actively control metamaterials using molecular interactions and, in turn, to use metamaterials to control molecular processes.

Ultrasensitive Detection of Biomarkers in a Color-Switchable Microcavity-Reactor Laser

Early detection and diagnosis are vitally important in reducing the mortality rate of fatal diseases but require highly sensitive detection of biomarkers. Presently, detection methods with the highest sensitivity require in vitro processing, while in vivo compatible fluorescence detections require a much higher concentration of biomarkers or limit of detection (LOD). In this paper, a fundamentally new strategy for ultrasensitive detection based on color-switchable lasing with a cavity-enhanced reduction of LOD is demonstrated, down to 1.4 × 10-16  mg ml-1 for a quantitative detection, lower than both the fluorescence method and plasmonic enhanced method. For a qualitative or a yes/no type of detection, the LOD is as low as 10-17  mg ml-1 . The approach in this work is based on a dye-embedded, in vivo compatible, polystyrene-sphere cavity, penetrable by biomarkers. A polystyrene sphere serves the dual roles of a laser cavity and an in vivo bio-reactor, in which dye molecules react with a biomarker, reporting biomarker information through lasing signals. The cavity-enhanced emission and lasing with only a single biomarker molecule per cavity allow improved visual distinguishability via color changes. Furthermore, when combined with a narrow-band filter, the color-switchable lasers act as an "on-off" logic signal and can be integrated into multiplexing detection assay biochips.

Polar Semiconducting Scandium Nitride as an Infrared Plasmon and Phonon-Polaritonic Material

The interaction of light with collective charge oscillations, called plasmon-polariton, and with polar lattice vibrations, called phonon-polariton, are essential for confining light at deep subwavelength dimensions and achieving strong resonances. Traditionally, doped-semiconductors and conducting metal oxides (CMO) are used to achieve plasmon-polaritons in the near-to-mid infrared (IR), while polar dielectrics are utilized for realizing phonon-polaritons in the long-wavelength IR (LWIR) spectral regions. However, demonstrating low-loss plasmon- and phonon-polaritons in one host material will make it attractive for practical applications. Here, we demonstrate high-quality tunable short-wavelength IR (SWIR) plasmon-polariton and LWIR phonon-polariton in complementary metal-oxide-semiconductor compatible group III-V polar semiconducting scandium nitride (ScN) thin films. We achieve both resonances by utilizing n-type (oxygen) and p-type (magnesium) doping in ScN that allows modulation of carrier concentration from 5 × 10¹⁸ to 1.6 × 10²¹ cm^-3. Our work enables infrared nanophotonics with an epitaxial group III semiconducting nitride, opening the possibility for practical applications.

Strong mode coupling-enabled hybrid photon-plasmon laser with a microfiber-coupled nanorod

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticles enabled by strong mode coupling. We show that, by strongly coupling a gold nanorod (GNR) with the whispering gallery cavity of a dye-doped polymer microfiber (with diameter down to 2.0 μm), the substantially enhanced optical coherence of the hybrid photon-plasmon mode and effective gain accumulated from the active microfiber cavity enable single-mode laser emission from the GNR at room temperature with a threshold as low as 2.71 MW/cm² and a linewidth narrower than 2 nm.

Photonic Nanolaser with Extreme Optical Field Confinement

We proposed a photonic approach to a lasing mode supported by low-loss oscillation of polarized bound electrons in an active nano-slit-waveguide cavity, which circumvents the confinement-loss trade-off of nanoplasmonics, and offers an optical confinement down to sub-1-nm level with a peak-to-background ratio of ∼30  dB. Experimentally, the extremely confined lasing field is realized as the dominant peak of a TE_{0}-like lasing mode around 720-nm wavelength, in 1-nm-level width slit-waveguide cavities in coupled CdSe nanowire pairs. The measured lasing characteristics agree well with the theoretical calculations. Our results may pave a way towards new regions for nanolasers and light-matter interaction.

Electrically driven single microwire-based single-mode microlaser

Engineering the lasing-mode oscillations effectively within a laser cavity is a relatively updated attentive study and perplexing issue in the field of laser physics and applications. Herein, we report a realization of electrically driven single-mode microlaser, which is composed of gallium incorporated zinc oxide microwire (ZnO:Ga MW) with platinum nanoparticles (PtNPs, d ~ 130 nm) covering, a magnesium oxide (MgO) nanofilm, a Pt nanofilm, and a p-type GaN substrate. The laser cavity modes could resonate following the whispering-gallery mode (WGM) among the six side surfaces by total internal reflection, and the single-mode lasing wavelength is centered at 390.5 nm with a linewidth of about 0.18 nm. The cavity quality factor Q is evaluated to about 2169. In the laser structure, the usage of Pt and MgO buffer layers can be utilized to engineer the band alignment of ZnO:Ga/GaN heterojunction, optimize the p-n junction quality and increase the current injection. Thus, the well-designed device structure can seamlessly unite the electron-hole recombination region, the gain medium, and optical microresonator into the PtNPs@ZnO:Ga wire perfectly. Such a single MW microlaser is essentially single-mode regardless of the gain spectral bandwidth. To study the single-mode operation, PtNPs working as superabsorber can engineering the multimode lasing actions of ZnO:Ga MWs even if their dimensions are typically much larger than that of lasing wavelength. Our findings can provide a straightforward and effective scheme to develop single-mode microlaser devices based on one-dimensional wire semiconductors.

Mode-dependent energy exchange between near- and far-field through silicon-supported single silver nanorods

Optical antenna effects endow plasmonic nanoparticles with the capability to enhance and control various types of light-matter interaction. Most reported plasmonic systems can be regarded as single-channel nanoantennas, which rely only on a bright dipole plasmon mode for energy exchange between near- and far-field. Herein we demonstrate a dual-channel plasmonic system that can separate the excitation and emission processes into two energy exchange pathways mediated by the different plasmon modes, offering a higher degree of freedom for the manipulation of light-matter interaction. Our system, consisting of high-aspect-ratio Ag nanorods and Si substrates, can support a series of bright and dark plasmon modes with distinct near- and far-field properties and generate relatively intensive local field enhancement in the gap region. As a proof-of-principle, we take plasmon-enhanced fluorescence of dye molecules as an example to reveal the energy exchange mechanism in the dual-channel plasmonic system. Such a system is potentially also useful for manipulating other types of light-matter interaction. Our work represents a step toward the utilization of a broader class of plasmon resonance for the development of optical antennas and various on-chip nanophotonic components.

Perampanel Reduces Brain Damage via Induction of M2 Microglia in a Neonatal Rat Stroke Model

Purpose

Ischemic stroke is a leading cause of death and disability worldwide. Additionally, neonatal ischemia is a common cause of neonatal brain injury, resulting in cerebral palsy with subsequent learning disabilities and epilepsy. However, there is currently a lack of effective treatments available for patients with perinatal ischemic stroke. In this study, we investigated the effect of perampanel (PER)-loaded poly lactic-co-glycolic acid (PLGA) by targeting microglia in perinatal stroke.

Methods

After formation of focal ischemic stroke by photothrombosis in P7 rats, PER-loaded PLGA was injected intrathecally. Proinflammatory markers (TNF-α, IL-1β, IL-6, COX2, and iNOS) and M2 polarization markers (Ym1 and Arg1) were evaluated. We investigated whether PER increased M2 microglial polarization in vitro.

Results

PER-loaded PLGA nanoparticles decreased the pro-inflammatory cytokines compared to the control group. Furthermore, they increased M2 polarization.

Conclusion

PER-loaded PLGA nanoparticles decreased the size of the infarct and increased motor function in a perinatal ischemic stroke rat model. Pro-inflammatory cytokines were also reduced compared to the control group. Finally, this development of a drug delivery system targeting microglia confirms the potential to develop new therapeutic agents for perinatal ischemic stroke.

Numerical study on a random plasmonic laser in the metal-insulator-metal structure

This Letter proposes a random plasmonic laser in the metal-insulator-metal (MIM) structure, in which the dielectric core with gain is dispersed with circular dielectric nanoscatterers. The numerical results from finite-difference time-domain simulation indicate that scattering by the randomly distributed dielectric nanoscatterers in the MIM waveguide provides feedback to the random laser with surface plasmon. The design bypasses the requirement of a distributed feedback structure for the plasmonic waveguide-based nanolasers, which is challenging and expensive in fabrication. Additionally, the MIM structure makes this type of random laser easily applicable to nanoscale integrated photonic devices and circuits.

Interfacial engineering of plasmonic nanoparticle metasurfaces

SignificanceMolecules interacting with metallic nanostructures can show tunable exciton-plasmon coupling, ranging from weak to strong. One factor that influences the interactions is the spatial organization of the molecules relative to the localized plasmon-enhanced electromagnetic fields. In this work, we show that the arrangement of aromatic dye molecules can be tuned within plasmonic hotspots by interfacial engineering of nanoparticle surfaces. By controlling the local chemical and physical interactions, we could modulate lasing thresholds. Surface-functionalized plasmonic metasurfaces open prospects for programmable light-matter interactions at the nanoscale.