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Surface lattice resonance supported on plasmonic nanoparticle arrays enhances light‐matter interactions for applications such as photoluminescence enhancement. The photoluminescence process is enhanced through confining light beyond the diffraction limit and inducing stronger light–matter interaction. In this work, the absorption mechanisms of plasmonic nanoparticle arrays embedded with photoluminescent absorbers are analyzed. A modified coupled‐mode theory that describes the optical behavior of the surface lattice resonance was developed and verified by numerical simulations. Based on the analytical model, different components of the absorption contributed by the nanoparticles and the absorbers as well as the resonant properties of each of the components are identified. The origin of difference in resonant behavior with different materials is also discovered by exploring the nearfield characteristics of surface lattice resonance composed with a variety of materials. [ABSTRACT FROM AUTHOR]

All‐dielectric metasurfaces supporting high‐Q resonances have emerged as a promising platform for sensing applications. However, the greatly enhanced near‐fields are usually confined within the all‐dielectric nanostructures rather than the outside analyte region, severely limiting the bulk sensitivity and the biosensing performance. Here, a silicon metasurface formed by the hybridization of two lattices with a relative displacement is designed to support nonlocal quasi‐bound states in the continuum (q‐BICs) featuring homogeneous and significant near‐field enhancement over large volumes outside the silicon nanodisks. A high bulk sensitivity of 407 nm RIU–1 is experimentally demonstrated for the refractive index sensing applications, and a limit of detection down to 20 pg mL–1 for a protein biomarker for the early‐stage breast cancer screening, which is improved by more than an order of magnitude over the state of the art. It is expected that the nonlocal q‐BICs open new opportunities for realizing greatly enhanced light–matter interactions over large volumes in applications beyond biochemical sensing. [ABSTRACT FROM AUTHOR]

Surface lattice resonance supported on plasmonic nanoparticle arrays enhances light‐matter interactions for applications such as photoluminescence enhancement. The photoluminescence process is enhanced through confining light beyond the diffraction limit and inducing stronger light–matter interaction. In this work, the absorption mechanisms of plasmonic nanoparticle arrays embedded with photoluminescent absorbers are analyzed. A modified coupled‐mode theory that describes the optical behavior of the surface lattice resonance was developed and verified by numerical simulations. Based on the analytical model, different components of the absorption contributed by the nanoparticles and the absorbers as well as the resonant properties of each of the components are identified. The origin of difference in resonant behavior with different materials is also discovered by exploring the nearfield characteristics of surface lattice resonance composed with a variety of materials.

Silicon (Si) photovoltaic cells and their production play a pivotal role in advancing energy utilization within the rapidly expanding solar industry, which serves as a critical driver in realizing global sustainability objectives and mitigating environmental repercussions associated with energy production. Here, we introduce a novel two-step pattern transfer technique to successfully imprint a two-dimensional plasmonic micro-square periodic array onto an Si substrate, utilizing Kapton® Tape and plasma technology. Remarkably, this represents the first-ever application of flexible and stretchable Kapton® polyimide for pattern transfer onto Si. The vacuum plasma treatment plays a pivotal role in significantly enhancing surface adhesion performance, thereby facilitating the efficient pattern transfer process. As a result, the resulting microstructure exhibits exceptional performance as a plamonic broadband absorber in the visible region, making it a highly promising candidate for enhancing efficiency in Si-based solar cells. To support our experimental findings, the finite-difference time domain method was employed for simulating the fabricated plasmonic structure and determining the electric field distribution. The simulation results unequivocally affirm the robust and intense light trapping capabilities of the microstructure. Moreover, our fabrication technique demonstrates the potential for achieving high-resolution microstructure through an innovative, straightforward, and cost-efficient approach. [ABSTRACT FROM AUTHOR]

We investigated the changes in shape and extinction intensity of Au nanorod arrays by rapid thermal annealing (RTA). RTA was performed at 400~800°C for 3 min in an N2 atmosphere using a halogen lamp as a heater. With increasing annealing temperature, the surface roughness of the rod decreases, the long axis of the rod shrinks while the short axis inflates, and finally some rods split. The wavelength and intensity of localized surface plasmon resonance varied with the rods shape. In particular, annealing at 800°C shifts the high-order (3λ/2) mode along the long axis from the near infrared to the visible region. Also surface lattice resonance is observed, showing that the periodicity of the array is retained even after annealing at 800°C. [ABSTRACT FROM AUTHOR]

A self‐confined solid‐state dewetting mechanism is reported that can fundamentally reduce the use of sophisticated nanofabrication techniques, enabling efficient wafer‐scale patterning of non‐closely packed (ncp) gold nanoparticle arrays. When combined with a soft lithography process, this approach can address the reproducibility challenges associated with colloidal crystal self‐assembly, allowing for the batch fabrication of ncp gold arrays with consistent ordering and even optical properties. The resulting dewetted ncp gold nanoparticle arrays exhibit strong surface lattice resonance properties when excited in inhomogeneous environments under normal white‐light incidence. With these SLR properties, the sensitive plasmonic sensing of molecular interactions is achieved using a simple transmission setup. This study will advance the development of miniaturized and portable devices. [ABSTRACT FROM AUTHOR]

A high-performance resonant metasurface is rather promising for diverse application areas such as optical sensing and filtering. Herein, a metal–insulator–metal (MIM) optical sensor with merits of a high quality-factor (Q-factor), multiple operating bands, and high spectrum contrast is proposed using plasmonic square bracket dimer metasurface. Due to the complex square bracket itself, a dimer structure of two oppositely placed square brackets, and metasurface array configuration, multiple kinds of mode coupling can be devised in the inner and outer elements within the metasurface, enabling four sensing channels with the sensitivities higher than 200 nm/RIU for refractive index sensing. Among them, the special sensing channel based on the reflection-type surface lattice resonance (SLR) mechanism has a full width at half maximum (FWHM) of only 2 nm, a high peak-to-dip signal contrast of 0.82, a high Q-factor of 548, and it can also behave as a good sensing channel for the thickness measurement of the deposition layer. The multi-band sensor can work normally in a large refractive index or thickness range, and the number of resonant channels can be further increased by simply breaking the structural symmetry or changing the polarization angle of incident light. Equipped with unique advantages, the suggested plasmonic metasurface has great potential in sensing, monitoring, filtering, and other applications. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally that a one-dimensional array of silicon nanowires periodically placed on a nickel substrate enhances the transverse magneto-optical Kerr effect (TMOKE) compared to a nickel film. The enhancement mechanism is associated with the excitation of two types of resonances: multipole Mie resonances in each nanowire and surface lattice resonances (SLRs) emerging from the periodic arrangement of the nanowires. The maximal TMOKE values reached up to 1.9 and 2.6% due to the excitation of SLR and a magnetic dipole resonance, respectively. When the SLR is excited, the spectral width of the TMOKE enhancement is narrower compared to the case of the magnetic dipole resonance. [ABSTRACT FROM AUTHOR]

A giant electric field on a subwavelength scale is highly beneficial for boosting the light–matter interaction. In this paper, we investigated a hybrid structure consisting of a hemispheric dimer array and a gold film and realized resonant mode coupling of the surface lattice resonance (SLR) and surface plasmon polariton (SPP). Mode coupling is demonstrated by observing anti-crossing in reflection spectra, which corresponds to Rabi splitting. Although the resonance coupling does not enter the strong coupling regime, an improved quality factor (Q~350) and stronger electric field enhancement in the gap region of the dimer (i.e., hot spot) in our hybrid structure are obtained compared to those of the single dimer or dimer array only. Remarkably, the magnitude of electric field enhancement over 500 can be accessible. Such high field enhancement makes our hybridized structure a versatile platform for the realization of ultra-sensitive biosensing, low-threshold nanolasing, low-power nonlinear optical devices, etc. [ABSTRACT FROM AUTHOR]

Abstract A self‐confined solid‐state dewetting mechanism is reported that can fundamentally reduce the use of sophisticated nanofabrication techniques, enabling efficient wafer‐scale patterning of non‐closely packed (ncp) gold nanoparticle arrays. When combined with a soft lithography process, this approach can address the reproducibility challenges associated with colloidal crystal self‐assembly, allowing for the batch fabrication of ncp gold arrays with consistent ordering and even optical properties. The resulting dewetted ncp gold nanoparticle arrays exhibit strong surface lattice resonance properties when excited in inhomogeneous environments under normal white‐light incidence. With these SLR properties, the sensitive plasmonic sensing of molecular interactions is achieved using a simple transmission setup. This study will advance the development of miniaturized and portable devices.

Optical binding of metal nanoparticles (NPs) provides a promising way to create tunable photonic materials and devices, where the ultrastrong interparticle interaction is generally attributed to the localized surface plasmon resonances of NPs. Here, it is revealed that the optical binding of metal NPs can be self‐reinforced by the plasmonic surface lattice resonances (PSLRs) associated with the discrete NP arrays. Through simulations and experiments, it is demonstrated that PSLRs can spontaneously arise in optically bound gold NP chains with just a few NPs when they are relatively large, e.g., 150 nm in diameter. Additionally, the PSLRs are enhanced by increasing the chain length, leading to stronger optical binding stiffness. These results reveal a previously unidentified factor that contributes to the ultrastrong optical binding of metal NPs. More importantly, this study presents a prospect for building freestanding and reconfigurable NP arrays that naturally support PLSRs for sensing and other applications. [ABSTRACT FROM AUTHOR]

Bound states in the continuum (BICs) have been of growing interest in photonics for their infinite quality factors and strong field localization. The last decade has witnessed great progress on the highest achievable quality factors of quasi‐BICs. However, it remains challenging to realize robust high‐Q quasi‐BICs that are tolerant to the parameter perturbation. Here, it is demonstrated that silicon metasurfaces formed by the hybridization of two lattices can support robust quasi‐BICs with the highest measured quality factor reaching 4130 and the minimum one larger than 1024, even when the relative displacement varies over the whole range of all the possible values. Taking advantage of the two in‐plane mirror‐symmetry points, for the first time, the transition between a toroidal dipole BIC and an electric quadrupole BIC, which guarantees robust ultrahigh‐Q quasi‐BICs at Γ point, is reported. The minimum quality factors of quasi‐BICs can be further improved significantly by shrinking the meta‐atom size and are immune from the intrinsic absorption loss of silicon in the visible regime. It is envisioned that this study will pave the way for achieving robust ultrahigh‐Q metasurfaces and boost their applications in lasing, nonlinear optics, and biosensing. [ABSTRACT FROM AUTHOR]

In the field of localized surface plasmon resonance sensing, narrow linewidth, high-quality factor, and high absorptivity have always been the goals that researchers are committed to achieving. The primary methods for achieving this goal are near-field coupling and far-field coupling. Due to the limitations of nanomanufacturing processes, current research often only focuses on single coupling methods such as far-field coupling or near-field coupling, with few relevant reports combining the two coupling methods. Based on this, this paper proposes a single-layer gold nano-disk array structure, which is simple and easy to manufacture. Through modal field analysis and structural parameter adjustment, some significant results have been achieved. On the one hand, the suggested gold nano-disk array structure yields a resonant peak based on far-field coupling with a full width at half maximum (FWHM) of less than 0.05 nm and a figure of merit of more than 15 000 RI U − 1 (the quality factor is more than 20 000). On the other hand, it has been successfully accomplished to combine near-field coupling and far-field coupling, leading to a composite coupling peak that incorporates the benefits of both types of coupling. Moreover, this coupling peak has excellent characteristics such as narrow FWHM (less than 3 nm) and high absorptivity (up to 80.5%), which is superior to most reported sensing structures and more in line with practical sensing application requirements. In this paper, the potential of the gold disk array structure as a high-performance sensing structure is further explored, providing reference and new ideas for the design of easy-to-prepare and high-performance electromagnetic resonance devices. [ABSTRACT FROM AUTHOR]

A high-performance resonant metasurface is rather promising for diverse application areas such as optical sensing and filtering. Herein, a metal–insulator–metal (MIM) optical sensor with merits of a high quality-factor (Q-factor), multiple operating bands, and high spectrum contrast is proposed using plasmonic square bracket dimer metasurface. Due to the complex square bracket itself, a dimer structure of two oppositely placed square brackets, and metasurface array configuration, multiple kinds of mode coupling can be devised in the inner and outer elements within the metasurface, enabling four sensing channels with the sensitivities higher than 200 nm/RIU for refractive index sensing. Among them, the special sensing channel based on the reflection-type surface lattice resonance (SLR) mechanism has a full width at half maximum (FWHM) of only 2 nm, a high peak-to-dip signal contrast of 0.82, a high Q-factor of 548, and it can also behave as a good sensing channel for the thickness measurement of the deposition layer. The multi-band sensor can work normally in a large refractive index or thickness range, and the number of resonant channels can be further increased by simply breaking the structural symmetry or changing the polarization angle of incident light. Equipped with unique advantages, the suggested plasmonic metasurface has great potential in sensing, monitoring, filtering, and other applications.

A giant electric field on a subwavelength scale is highly beneficial for boosting the light–matter interaction. In this paper, we investigated a hybrid structure consisting of a hemispheric dimer array and a gold film and realized resonant mode coupling of the surface lattice resonance (SLR) and surface plasmon polariton (SPP). Mode coupling is demonstrated by observing anti-crossing in reflection spectra, which corresponds to Rabi splitting. Although the resonance coupling does not enter the strong coupling regime, an improved quality factor (Q~350) and stronger electric field enhancement in the gap region of the dimer (i.e., hot spot) in our hybrid structure are obtained compared to those of the single dimer or dimer array only. Remarkably, the magnitude of electric field enhancement over 500 can be accessible. Such high field enhancement makes our hybridized structure a versatile platform for the realization of ultra-sensitive biosensing, low-threshold nanolasing, low-power nonlinear optical devices, etc.

Strong light–matter interaction plays a central role in realizing quantum photonic technologies. The entanglement state, which results from the hybridization of excitons and cavity photons, forms the foundation of quantum information science. In this work, an entanglement state is achieved by manipulating the mode coupling between surface lattice resonance and quantum emitter into the strong coupling regime. At the same time, a Rabi splitting of 40 meV is observed. A full quantum model based on the Heisenberg picture is used to describe this unclassical phenomenon, and it perfectly explains the interaction and dissipation process. In addition, the observed concurrency degree of the entanglement state is 0.5, presenting the quantum nonlocality. This work effectively contributes to the understanding of nonclassical quantum effects arising from strong coupling and will intrigue more interesting potential applications in quantum optics. [ABSTRACT FROM AUTHOR]

[Display omitted] Three-dimensional plasmonic nanoparticle arrays in which the nanoparticles are assembled with a certain distance apart are expected to exhibit unique optical properties attributed to surface lattice resonances because of the interactions between the nanoparticle layers. Multi-layered gold nanoparticle arrays were created to experimentally prove surface lattice resonances from three-dimensional arrays. Silica-coated gold nanoparticles were employed as building blocks for the array because the distance between the nanoparticles can be tuned by adjusting the thickness of the silica coating. Employing highly monodisperse building blocks enabled to fabricate both single-layered and multi-layered plasmonic arrays via a confined convective assembly method. Multi-layering of monodisperse building blocks brought about some additional peaks corresponded to Bragg diffraction of gold nanoparticle periodic array and the interactions between layers in a hexagonal close-packed structure of the nanoparticles, respectively. Most importantly, the multi-layered arrays exhibited a distinctive extinction peak at the same wavelength as that observed from the single-layered array, proving the realization of surface lattice resonances from the three-dimensional plasmonic array. [ABSTRACT FROM AUTHOR]

The impact of plasmonic surface lattice resonances on the magneto‐optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt]N multilayer nanodisks. Varying the light wavelength, the disk diameter, and the period of the array, it is demonstrated that surface lattice resonances allow all‐optical single pulse switching of [Co/Gd/Pt]N nanodisk arrays with an energy 400% smaller than the energy needed to switch a continuous [Co/Gd/Pt]N film. Moreover, the magneto‐optical Faraday effect is enhanced at the resonance condition by up to 5,000%. The influence of the disk diameter and array period on the amplitude, width and position of the surface lattice resonances is in qualitative agreement with theoretical calculations and opens the way to designing magnetic metasurfaces for all‐optical magnetization switching applications. [ABSTRACT FROM AUTHOR]

Metasurfaces have demonstrated their sensing capabilities in the terahertz (THz) region. However, the practical application of these technologies is constrained by the complexity of their structural design and the randomness of their sensing performance. In this work, we propose a novel THz sensor based on a surface lattice resonance (SLR) metasurface with high refractive index (RI) sensitivity (502.8 GHz/RIU), high-quality factor (Q) (164.4), and simple structural design. The high sensing performance is attributed to the SLR generated by the coupling of Rayleigh anomaly (RA) diffraction and spoof localized surface plasmons in the metasurface. In the experiment, 0.9 % (0.1538 mol/L) sodium chloride (NaCl) solution with human physiological concentration can cause a 246.8 GHz shift of the SLR peak. Furthermore, the sensor demonstrates a blue-shift of the SLR peak with the decrease of the structural period of the metasurface, and meanwhile, its RI sensitivity increases with regularity. This work provides a new method for detecting health indicators of human physiological concentration by designing highly sensitive THz metasurface for a specific frequency. [Display omitted] • Terahertz metasurfaces based on surface lattice resonances have a simple design that enables efficient biochemical sensing. [ABSTRACT FROM AUTHOR]

Abstract The impact of plasmonic surface lattice resonances on the magneto‐optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt]N multilayer nanodisks. Varying the light wavelength, the disk diameter, and the period of the array, it is demonstrated that surface lattice resonances allow all‐optical single pulse switching of [Co/Gd/Pt]N nanodisk arrays with an energy 400% smaller than the energy needed to switch a continuous [Co/Gd/Pt]N film. Moreover, the magneto‐optical Faraday effect is enhanced at the resonance condition by up to 5,000%. The influence of the disk diameter and array period on the amplitude, width and position of the surface lattice resonances is in qualitative agreement with theoretical calculations and opens the way to designing magnetic metasurfaces for all‐optical magnetization switching applications.

Surface lattice resonances (SLRs) with high-quality factors supported by metal nanoparticle arrays are useful for plasmonic nanolasers, biochemical sensors, and surface-enhanced Raman spectroscopy. Most nanoparticle arrays are fabricated on a substrate, and the refractive index mismatch between the substrate and superstrate suppresses the performance of SLRs. In this work, we propose unique SLRs excited in suspended, self-aligned symmetric double-layer gratings with index-matched environment. The self-aligned double-layer gratings are fabricated using a single-step electron beam lithography and exhibit a Fano-like spectra resulting from interference between out-of-plane plasmonic resonances and diffraction modes. By changing the incident angle and refractive index of the surrounding medium, the SLRs can be tuned from visible to near-infrared regions with a high-quality factor of 120. [ABSTRACT FROM AUTHOR]

The capability of plasmonic metasurfaces (PMs) under illumination to generate heat and induce fluid convection is a promising building approach for optofluidic applications. However, the low quality (Q)‐factor in PMs introduced into optofluidic applications remains a challenging problem. In this paper, a PM optofluidic platform based on surface lattice resonance (SLR) with a high Q‐factor is proposed. Numerical results demonstrate that SLR‐based metasurfaces can manipulate the convective flow of fluid at the nanoscale, with the Q‐factor approaching 138. Moreover, compared to the localized surface plasmon resonance‐based metasurface, the SLR‐based metasurfaces exhibit improved absorption, temperature rise, and flow velocity performance. In particular, the absorption coefficient at the SLR peak in an adequately designed PM can be close to unity. This study reveals that SLR is an efficient and alternative method to manipulate the fluid flow, and paves the way to flexible wavelength‐scale devices for optofluidic applications. [ABSTRACT FROM AUTHOR]

Abstarct: An ultra-narrow-band perfect absorber based on collective resonances in an Ag nanoring period array is theoretically proposed for the absorption enhancement of monolayer graphene, where the absorptivity can reach as high as 99.4% with the full-width-half-maximum as narrow as 3.6 nm in the visible band. This outstanding absorptive characteristic can be attributed to the excitation of surface lattice resonance modes by Ag nanoring periodic array. The as-designed structure possesses high refractive-index sensitivity, reaching 557.9 nm RIUâˆ'1 with its figure of merit attaining 155 RIUâˆ'1. This work provides promising guidance for developing high-performance graphene-based photonic devices. [ABSTRACT FROM AUTHOR]

Dielectric metasurfaces have shown prominent applications in nonlinear optics due to strong field enhancement and low dissipation losses at the nanoscale. Chalcogenide glasses are one of the promising materials for the observation of nonlinear effects thanks to their high intrinsic nonlinearities. Here, we demonstrate, experimentally and theoretically, that significant second harmonic generation (SHG) can be obtained within amorphous Selenium (Se)-based chalcogenide metasurfaces by exploiting the coupling between lattice and particle resonances. We further show that the high-quality factor resonance at the origin of the SHG can be tuned over a wide wavelength range using a simple and versatile fabrication approach. The measured second harmonic intensity is orders of magnitude higher than that from a dewetted Se film consisting of random Se nanoparticles. The achieved conversion efficiency in the resonance region is of the order of 10−6 which is comparable with direct bandgap materials and at least two orders of magnitude higher than that of conventional plasmonics- and Si-based structures. Fabricated via a simple and scalable technique, these all-dielectric architectures are ideal candidates for the design of flat nonlinear optical components on flexible substrates.

We proposed a dual-band polarization-insensitive metamaterial absorber consisting of merely the square metallic patch and a continuous metallic ground separated by a middle dielectric layer. Two resonance peaks derived from 'the fundamental resonance (with 97% absorbance) and the surface lattice resonance (with 99% absorbance) are realized. It is different from previous work that the dual-band response is obtained by combining two resonances of different sizes. Moreover, a first-order diffraction mode of grating predicts the resonance wavelength of the proposed absorber. The surface electromagnetic field distributions of the unit-cell structure reveal the physical origin of the dual-band absorption. Importantly, the first absorption peak results from surface lattice resonance with narrow line-width has large sensitivity perform and high-quality factor, which has significant potential in the application of the biosensors and monitoring. [ABSTRACT FROM AUTHOR]

In the last few decades, plasmonic colorimetric biosensors raised increasing interest in bioanalytics thanks to their cost-effectiveness, responsiveness, and simplicity as compared to conventional laboratory techniques. Potential high-throughput screening and easy-to-use assay procedures make them also suitable for realizing point of care devices. Nevertheless, several challenges such as fabrication complexity, laborious biofunctionalization, and poor sensitivity compromise their technological transfer from research laboratories to industry and, hence, still hamper their adoption on large-scale. However, newly-developing plasmonic colorimetric biosensors boast impressive sensing performance in terms of sensitivity, dynamic range, limit of detection, reliability, and specificity thereby continuously encouraging further researches. In this review, recently reported plasmonic colorimetric biosensors are discussed with a focus on the following categories: (i) on-platform-based (localized surface plasmon resonance, coupled plasmon resonance and surface lattice resonance); (ii) colloid aggregation-based (label-based and label free); (iii) colloid non-aggregation-based (nanozyme, etching-based and growth-based). [ABSTRACT FROM AUTHOR]

Conventional laboratory techniques exhibit impressive sensing performance and still constitute an irreplaceable tool in bioanalytics. Nevertheless, high costs, time consumption, and need for well‐equipped laboratories and skilled personnel make highly desirable to explore novel strategies to carry out biochemical analyses. In this regard, biosensor‐based methods represent a promising approach to keep affordability and rapidity, thus they can inherently pave the way to point of care tests and high‐throughput analysis. Regrettably, most of them suffer from fabrication and biofunctionalization complexity, and poor sensitivities and reliability. Therefore, their adoption as a real alternative to the gold standards is still far from being achieved. However, the massive research on plasmonic nanostructures is revealing their potentialities in sensing field, since they own appealing performances resulting from the plasmon‐related effects and can be easily adapted to a large variety of applications. In this review, a summary of plasmonic biosensors recently devised is reported. Though many nanostructures fit for shared applications, for clarity they are classified into two main categories: i) biosensors whose sensing parameters are plasmon‐related observables (localized, coupled, lattice surface plasmon resonances) and ii) biosensors in which the nanostructure acts as amplifier for an external signal (surface‐enhanced Raman and infrared spectroscopies and plasmon‐enhanced fluorescence). [ABSTRACT FROM AUTHOR]

Enhancing the circular dichroism signals of chiral plasmonic nanostructures is vital for realizing miniaturized functional chiroptical devices, such as ultrathin wave plates and high-performance chiral biosensors. Rationally assembling individual plasmonic metamolecules into coupled nanoclusters or periodic arrays provides an extra degree of freedom to effectively manipulate and leverage the intrinsic circular dichroism of the constituent structures. Here, we show that sophisticated manipulation over the geometric parameters of a plasmonic stereo-metamolecule array enables selective excitation of its surface lattice resonance mode either by left- or right-handed circularly polarized incidence through diffraction coupling, which can significantly amplify the differential absorption and hence the intrinsic circular dichroism. In particular, since the diffraction coupling requires no index-matching condition and its handedness can be switched by manipulating the refractive index of either the superstrate or the substrate, it is therefore possible to achieve dynamic tuning and active control of the intrinsic circular dichroism response without the need of modifying structure parameters. Our proposed system provides a versatile platform for ultrasensitive chiral plasmonics biosensing and light field manipulation.

Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large‐scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a‐GaP), over the visible spectrum. It is shown that cost‐effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface. [ABSTRACT FROM AUTHOR]

Surface lattice resonances (SLRs) with high-quality factors supported by metal nanoparticle arrays are useful for plasmonic nanolasers, biochemical sensors, and surface-enhanced Raman spectroscopy. Most nanoparticle arrays are fabricated on a substrate, and the refractive index mismatch between the substrate and superstrate suppresses the performance of SLRs. In this work, we propose unique SLRs excited in suspended, self-aligned symmetric double-layer gratings with index-matched environment. The self-aligned double-layer gratings are fabricated using a single-step electron beam lithography and exhibit a Fano-like spectra resulting from interference between out-of-plane plasmonic resonances and diffraction modes. By changing the incident angle and refractive index of the surrounding medium, the SLRs can be tuned from visible to near-infrared regions with a high-quality factor of 120.

The hybrid plasmonic surface lattice resonance (SLR) laser constructed by a MAPbBr3 perovskite thin film on the Ag nanoparticle array is unambiguously demonstrated in this research. The relatively high refractive index of the perovskite thin film provides an excellent coupling between the photonic mode and SLR, leading to a high spontaneous emission coupling factor and a low threshold lasing. Furthermore, a novel spin‐coating process applied to grow the MAPbBr3 perovskite thin film can leave air gaps under the perovskite that provides a large index difference in the periodic array, making the hybrid plasmonic SLR exhibits a high density of state, which is beneficial for laser operation. Via theoretical design and experimental verification, the lasing behaviors of the hybrid plasmonic SLR perovskite laser show excellent characteristics with a fixed polarization. This demonstration facilitates an enhanced lasing performance and realization of the low‐cost and low‐energy‐consumption laser application. [ABSTRACT FROM AUTHOR]

Due to its ability to concentrate electromagnetic waves into deep sub-wavelength volume, surface plasmons have been widely used in nanophotonics. Generally, surface plasmons can be divided into two categories: surface plasmon polaritons (SPPs) propagating along the interface between metal and medium, and localized surface plasmon resonance (LSPRs) bound to metal surface. There is an obvious momentum mismatch between SPPs and the corresponding free space electromagnetic wave. Grating, i. e. one-dimensional plasmonic lattice, is often used to compensate for this momentum mismatch and launch SPPs from free space. LSPRs refer to the surface plasmon localized around a single nanostructure under external light field excitation. When LSPRs are launched, the near-field enhancement effect can greatly increase the absorption and scattering of the incident light. In fact, one dimensional plasmon lattice supports both SPPs and LSPRs, which is an excellent foundamental structure for studying surface plasmon and its optical properties. Due to the coexistence of LSPR, there are much richer energy band structures in plasmonic lattice than in photonic crystals. In this review, we focus on onedimensional plasmon lattice, and discuss the novel properties of metal plasmon from four aspects: band control, surface lattice resonance, bound states in continuum and Bose-Einstein condensation. These properties are of great significance to further promote the application of surface plasmon. [ABSTRACT FROM AUTHOR]

The field of magnetoplasmonics exploits interactions between light and magnetic matter at the nanoscale for light manipulation and resonant magneto-optics. One of the great challenges of this field is overcoming optical losses in magnetic metals. Here, we exploit surface plasmon polaritons (SPPs) excited at the interface of an SiO2/Au bilayer to induce strong magneto-optical responses on the Ni nanodisks of a periodic array. Using a reference system made of Au nanodisks, we show that optical losses in Ni hardly broaden the linewidth of SPP-driven magneto-optical signals. Loss mitigation is attained because the free electrons in the Ni nanodisks are driven into forced oscillations away from their plasmon resonance. By varying the SiO2 layer thickness and lattice constant of the Ni nanodisk array, we demonstrate tailoring of intense magneto-optical Kerr effects with a spectral linewidth down to ~25 nm. Our results provide important hints on how to circumvent optical losses and enhance magneto-optical signals via the design of off-resonance magnetoplasmonic driving mechanisms.

The cooperative phenomena stemming from the radiation field-mediated coupling between individual quantum emitters are presently attracting broad interest for applications related to on-chip photonic quantum memories and long-range entanglement. Common to these applications is the generation of electro-magnetic modes over macroscopic distances. Much research, however, is still needed before such systems can be deployed in the form of practical devices, starting with the investigation of alternate physical platforms. Quantum emitters in two-dimensional (2D) systems provide an intriguing route because these materials can be adapted to arbitrarily shaped substrates to form hybrid systems wherein emitters are near-field-coupled to suitable optical modes. Here, we report a scalable coupling method allowing color center ensembles in a van der Waals material (hexagonal boron nitride) to couple to a delocalized high-quality plasmonic surface lattice resonance. This type of architecture is promising for photonic applications, especially given the ability of the hexagonal boron nitride emitters to operate as single-photon sources at room temperature.

Engineering nanostructures with exceptionally high-Q resonances mediated by the Fano-type hybridization between discrete states associated with the periodicity of the structure and broadband resonances excited on constituent scatterers are the emerging field in optics and photonics. These collective lattice resonances (CLRs) attracted a lot of attention in recent years due to a number of their exciting applications in sensing, optical filtering, structural color printing, fluorescence enhancement, nanoscale lasing, and nonlinear optics, which resulted in a rapidly growing number of fundamental and experimental studies. CLRs have been discovered for arrays of plasmonic metal nanoparticles with strong electric dipole resonances nearly four decades ago. Thereafter, the scope of CLRs has gradually extended to all-dielectric and magneto-optical nanoparticles, 2D materials and other types of constituents, which has broadened the range of CLRs applicability and enriched their properties. We provide a comprehensive review of the recent progress in this field with a special emphasis on advances far beyond plasmonics.

We propose a novel configuration for nonvolatile and reconfigurable tuning of surface lattice resonances (SLRs) based on thin films of phase-change material Ge2Sb2Te5 (GST). The configuration is composed of gold nanorod array embedded in a thin GST film. Results show that, an extremely wide SLR wavelength tuning range reaching 1600 nm, large tuning figure of merit of 21, and high SLR quality factors of 47 and 17 can be achieved in the mid-infrared regime when GST transits from the amorphous state into the crystalline state. The effects of the GST layer thicknesses on the SLR tuning performance are discussed, and the performances of several modified configurations are compared. We expect this work will advance the engineering of SLR tuning based on phase-change materials and promote its applications especially in nanolasing and narrowband filtering.

We report the strong coupling between plasmonic surface lattice resonances (SLRs) and photonic Fabry-Pérot (F-P) resonances in a microcavity embedded with two-dimensional periodic array of metal-insulator-metal nanopillars. For such a plasmonic-photonic system, we show that the SLR can be strongly coupled to the F-P resonances of both the odd- and even orders, and that the splitting energy reaches as high as 153 meV in the visible regime. Taking advantage of the strong coupling, the resulted high-energy upper polariton has similar characteristics as the plasmonic SLR, but the quality factor is almost twice of that of the SLR. We expect that this work will provide a new scheme for strong coupling between plasmonic and photonic modes, and will point to a new direction to improve the quality factor of SLRs.

Frequency conversion of light can be dramatically enhanced using high quality factor ( Q -factor) resonator. Unfortunately, the achievable conversion efficiencies and conversion bandwidths are fundamentally limited by the time–bandwidth limit of the resonator, restricting their use in frequency conversion of ultrashort pulses. Here, we propose and numerically demonstrate sum-frequency generation based frequency conversion using a metasurface-based resonator configuration that could overcome this limitation. The proposed experimental configuration takes use of the spatially dispersive responses of periodic metasurfaces supporting collective surface lattice resonances (SLRs), and can be utilized for broadband frequency conversion of ultrashort pulses. We investigate a plasmonic metasurface, supporting a high- Q SLR ( Q = 500, linewidth of 2 nm) centered near 1000 nm, and demonstrate ∼1000-fold enhancements of nonlinear signals. Furthermore, we demonstrate broadband frequency conversion with a pump conversion bandwidth reaching 75 nm, a value that greatly surpasses the linewidth of the studied resonator. Our work opens new avenues to utilize high- Q metasurfaces for broadband nonlinear frequency conversion.

The field of magnetoplasmonics exploits interactions between light and magnetic matter at the nanoscale for light manipulation and resonant magneto-optics. One of the great challenges of this field is overcoming optical losses in magnetic metals. Here, we exploit surface plasmon polaritons (SPPs) excited at the interface of an SiO2/Au bilayer to induce strong magneto-optical responses on the Ni nanodisks of a periodic array. Using a reference system made of Au nanodisks, we show that optical losses in Ni hardly broaden the linewidth of SPP-driven magneto-optical signals. Loss mitigation is attained because the free electrons in the Ni nanodisks are driven into forced oscillations away from their plasmon resonance. By varying the SiO2 layer thickness and lattice constant of the Ni nanodisk array, we demonstrate tailoring of intense magneto-optical Kerr effects with a spectral linewidth down to ~25 nm. Our results provide important hints on how to circumvent optical losses and enhance magneto-optical signals via the design of off-resonance magnetoplasmonic driving mechanisms. [ABSTRACT FROM AUTHOR]

Miniaturized and rationally assembled nanostructures exhibit extraordinarily distinct physical properties beyond their individual units. This review will focus on structured small-scale optical cavities, especially on plasmonic nanoparticle lattices that show unique electromagnetic near fields from collective optical coupling. By harnessing different material systems and structural designs, various light-matter interactions can be engineered, such as nanoscale lasing, nonlinear optics, and exciton-polariton coupling. Key device performance of nanoscale lasers will be discussed, including low power threshold, output tunability, and electrical pump. This review will also cover emerging applications of nanoscale optical cavities in quantum engineering. Structured nanoscale cavities can serve as a scalable platform for integrated photonic circuits and hybrid quantum photonic systems. [ABSTRACT FROM AUTHOR]

We propose a hybrid plasmonic zeolitic imidazolate framework-8 (ZIF-8) nanostructure to achieve near-infrared dual-band sensing of trace amounts of volatile organic compound (VOC) gases via metal-organic framework patch array integrated on metal (Au) film. To achieve dual-band VOC gas sensing, two absorption peaks related to the surface lattice resonance (SLR) and surface plasmon polaritons (SPP) resonance are constructed in this plasmonic structure, to match the near-infrared absorption bands of methane and ethanol gas molecules respectively. For an 80 nm thick Au layer, the height and width of ZIF-8 patch and the gap between ZIF-8 patches are optimized to be 0.86, 0.925, and 0.43 μm. Then, this structure shows an SLR at 1392.64 and a SPP resonance at 1653.72 nm, which have peak intensities of 0.735 and 0.855, and the Q-values of 1435 and 253, respectively. Furthermore, the third resonance peak related to the Fano resonance is investigated and can be considered as a feasible alternative to calibrate the measurement without external references. [ABSTRACT FROM AUTHOR]

This paper describes how metal-organic frameworks (MOFs) conformally coated on plasmonic nanoparticle arrays can support exciton-plasmon modes with features resembling strong coupling but that are better understood by a weak coupling model. Thin films of Zn-porphyrin MOFs were assembled by dip coating on arrays of silver nanoparticles (NP@MOF) that sustain surface lattice resonances (SLRs). Coupling of excitons with these lattice plasmons led to an SLR-like mixed mode in both transmission and transient absorption spectra. The spectral position of the mixed mode could be tailored by detuning the SLR in different refractive index environments and by changing the periodicity of the nanoparticle array. Photoluminescence showed mode splitting that can be interpreted as modulation of the exciton line shape by the Fano profile of the surface lattice mode, without requiring Rabi splitting. Compared with pristine Zn-porphyrin, hybrid NP@MOF structures achieved a 16-fold enhancement in emission intensity. Our results establish MOFs as a crystalline molecular emitter material that can couple with plasmonic structures for energy exchange and transfer. [ABSTRACT FROM AUTHOR]

Highlights • Incorporation of NPs array in PhC leads to emergence of additional Rayleigh anomalies. • Their position can be predicted with developed analytical model. • Spectral splittings can be tailored by varying structural parameters of the system. • The parity of mode coupling can be changed used the features of the field inside the PhC. Abstract We analytically and numerically study coupling mechanisms between 1D photonic crystal (PhC) and 2D array of plasmonic nanoparticles (NPs) embedded in its defect layer. We introduce general formalism to explain and predict the emergence of PhC-mediated Wood–Rayleigh anomalies, which spectral positions agree well with the results of exact simulations with Finite-Difference Time-Domain (FDTD) method. Electromagnetic coupling between localized surface plasmon resonance (LSPR) and PhC-mediated Wood–Rayleigh anomalies makes it possible to efficiently tailor PhC modes. The understanding of coupling mechanisms in such hybrid system paves a way for optimal design of sensors, light absorbers, modulators and other types of modern photonic devices with controllable optical properties. [ABSTRACT FROM AUTHOR]

Routine single-molecule analysis using surface-enhanced Raman scattering (SERS) is still out of reach using conventional substrates based on corrugated metallic surfaces. Tailoring the substrate to a specific excitation wavelength is an effective way to improve the SERS enhancement factor. Here, we present a comprehensive theoretical and experimental study of wavelength-tailored SERS substrates with improved sensitivity, exploiting the surface lattice resonance (SLR) in a plasmonic lattice comprised of assembled Ag nanoparticles. We tuned the SLR close to 532 nm and evaluated its effect on SERS. We found that SLR-based substrates had 10 times overall higher sensitivity and 100 times higher sensitivity at the target wavelength compared to non-tuned counterparts. Furthermore, we compared monomer and tetramer unit cell cases and found that the combined effect of tuned SLR and hot spots further improves the enhancement factor more than 400 times over a substrate with a random layer of nanoparticles. [Display omitted] • Capillarity-assisted nanoparticle deposition originates silver nanoparticle arrays. • SERS-active substrates with SLR in regular silver nanoparticle structures are shown. • Nanoparticle size variation allows tuning SLR position at the required wavelength. • The highest SERS response occurred when SLR and excitation laser wavelengths overlapped. • Hot spots integration into regular structure boosts SERS sensitivity. [ABSTRACT FROM AUTHOR]

We propose a nonvolatile, reconfigurable, and narrowband mid-infrared bandpass filter based on surface lattice resonance in phase-change material Ge2Sb2Te5. The proposed filter is composed of a two-dimensional gold nanorod array embedded in a thick Ge2Sb2Te5 film. Results show that when Ge2Sb2Te5 transits from the amorphous state to the crystalline state, the narrowband reflection spectrum of the proposed filter is tuned from 3.197 μm to 4.795 μm, covering the majority of the mid-infrared regime, the peak reflectance decreases from 72.6% to 25.8%, and the corresponding quality factor decreases from 19.6 to 10.3. We show that the spectral tuning range can be adjusted by varying the incidence angle or the lattice period. By properly designing the gold nanorod sizes, we also show that the quality factor can be greatly increased to 70 at the cost of relatively smaller peak reflection efficiencies, and that the peak reflection efficiency can be further increased to 80% at the cost of relatively smaller quality factors. We expect that this work will advance the engineering of Ge2Sb2Te5-based nonvalatile tunable surface lattice resonances and will promote their applications especially in reconfigurable narrowband filters.

Structural disorder can improve the optical properties of metasurfaces, whether it is emerging from some large-scale fabrication methods or explicitly designed and built lithographically. For example, correlated disorder, induced by a minimum inter-nanostructure distance or by hyperuniformity properties, is particularly beneficial for light extraction. Inspired by topology, we introduce numerical descriptors to provide quantitative measures of disorder with universal properties, suitable to treat both uncorrelated and correlated disorder at all length scales. The accuracy of these topological descriptors is illustrated both theoretically and experimentally by using them to design plasmonic metasurfaces with controlled disorder that we then correlate to the strength of their surface lattice resonances. These descriptors are an example of topological tools that can be used for the fast and accurate design of disordered structures or as aid in improving their fabrication methods.