Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near-infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the nano-objects with ultrashort laser pulses. Here, we synthesize core-shell gold-silver nanocuboids and measure their spectral signature in the stationary and ultrafast transient regimes. Their dipolar transverse mode vanishes with increasing Ag-shell thickness, while higher-order modes grow in the near-ultraviolet range where no plasmon resonance can be generated with single noble metal nanoparticles. These higher-energy modes are associated with sharp spectral variations of the ultrafast transient light extinction by the bimetallic nanocuboids. By carrying out a theoretical investigation, we break down the different contributions to this response and
Bimetallic plasmonic nanoparticles enable tuning of the optical response and chemical stability by variation of the composition. The present numerical simulation study compares Ag-Au alloy, Ag@Au core-shell, and Au@Ag core-shell bimetallic plasmonic nanoparticles of both spherical and anisotropic (nanotriangle and nanorods) shapes. By studying both spherical and anisotropic (with LSPR in the near-infrared region) shapes, cases with and without interband transitions of Au can be decoupled. Explicit comparisons are facilitated by numerical models supported by careful validation and examination o…
Incorporation of catalytically active materials into plasmonic metal nanostructures can efficiently merge the reactivity and energy harvesting abilities of both types of materials for visible light photocatalysis. Here we explore the influence of electromagnetic hotspots in the ability of plasmonic core-shell colloidal structures to induce chemical transformations. For this study, we developed a synthetic strategy for the fabrication of Au nanoparticle (NP) trimers in aqueous solution through fine controlled galvanic replacement between Ag nanoprisms and Au precursors. Core-shell Au@M NP trime…
We propose a novel approach for efficient tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser irradiation. This concept is based on ultrafast photo-injection of dense (>10^20 cm^-3) electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows to manipulate by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its scattering diagram and scattering cross section. We experimentally demonstrate 20 % tuning of refl…
The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system's electron gas, lattice and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution of the system subcomponents. We measured the dynamic optical response of ensembles of plasmonic Au nanoparticles following ultrashort-pulse excitation and we compared it with the corresponding static optical response as a function of the increasing temperatu…
We propose a novel concept for efficient dynamic tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser radiation. This concept is based on ultrafast generation of electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows to manipulate by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its extinction cross section and scattering diagram. Specifically, we demonstrate the effect of ultrafast switching-on a Hu…
Hybrid nanocomposites can offer a wide range of opportunities to control the light-matter interac- tion and electromagnetic energy flow at the nanoscale, leading to exotic optoelectronic devices. We study theoretically the dipole-dipole interaction in noble metal nanoparticles-graphene nanodisks- quantum dots hybrid systems in the optical region of the electromagnetic spectrum. The quantum dot is assumed to be a three-level atom interacting with ultrashort control and probe pulses in a Lambda configuration. The dynamics of the system are studied by numerically solving for the time evo- lution …
Optically generated electron-hole plasma in high-index dielectric nanostructures was demonstrated as a means of tuning of their optical properties. However, until now an ultrafast operation regime of such plasma driven nanostructures has not been attained. Here, we perform pump-probe experiments with resonant silicon nanoparticles and report on dense optical plasma generation near the magnetic dipole resonance with ultrafast (about 2.5 ps) relaxation rate. Basing on experimental results, we develop an analytical model describing transient response of a nanocrystalline silicon nanoparticle to a…
The full control of the fundamental photophysics of nanosystems at frequencies as high as few THz is key for tunable and ultrafast nano-photonic devices and metamaterials. Here we combine geometrical and ultrafast control of the optical properties of halide perovskite nanoparticles, which constitute a prominent platform for nanophotonics. The pulsed photoinjection of free carriers across the semiconducting gap leads to a sub-picosecond modification of the far-field electromagnetic properties that is fully controlled by the geometry of the system. When the nanoparticle size is tuned so as to ac…
We demonstrate theoretically that ultrafast heating of metal nanoparticles by the laser pulse should lead to the generation of coherent terahertz (THz) radiation during the heat redistribution process. It is shown that after the femtosecond laser pulse action the time-dependent gradient of the electronic temperature induces low-frequency particle polarization with the characteristic timescale of about fractions of picosecond. In the case of the directed metallic pattern, the THz pulse waveform can be controlled by changing geometry of the individual particle. The generation mechanism proposed …
The principle of optical trapping is conventionally based on the interaction of optical fields with linear induced polarizations. However, the optical force originating from the nonlinear polarization becomes significant when nonlinear optical nanoparticles are trapped by ultrafast laser pulses. Herein we establish the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate ultrafast laser pulses, based on the linear and nonlinear polarization effects. We investigate the dependence of the optical forces on the magnitudes and signs of the refractive nonlinear…
Ultrafast pump-probe measurements of plasmonic nanostructures probe the non-equilibrium behavior of excited carriers, which involves several competing effects obscured in typical empirical analyses. Here we present pump-probe measurements of plasmonic nanoparticles along with a complete theoretical description based on first-principles calculations of carrier dynamics and optical response, free of any fitting parameters. We account for detailed electronic-structure effects in the density of states, excited carrier distributions, electron-phonon coupling, and dielectric functions which allow us…
We consider light scattering by a coated magneto-plasmonic nanoparticle (MPNP) with a Kerr-type nonlinear plasmonic shell and a magneto-optic core. Such structure features two plasmon dipole modes, associated with electronic oscillations on the inner and outer surfaces of the shell. Driven in a nonlinear regime, each mode exhibits a bistable response. Bistability of an inner plasmon leads to switching between this state and a Fano resonance (Fano switching). Once the external light intensity exceeds the critical value, the bistability zones of both eigen modes overlap yielding optical tristabi…
We use ultrafast pump-probe transmission spectroscopy to measure the electronic relaxation time for electrons in cobalt nanoparticles embedded on glass substrate using femtosecond laser pulses. We found that the plasmon excitation is inhomogenously broadening with a fast excitation time of 23 fs. and a plasmonic relaxation time of 97fs. The femtosecond laser pulses used in this experiment were come from a Ti:Sapphire resonator that uses a self-mode-locking mechanism based on the nonlinear Kerr effect. The pulses were found to have repetition rate of 103.52MHz with a pulse width of 64.5 fs at F…
Non-equilibrium quantum plasmonics in nanoparticle-on-mirror nanocavities
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China（电子科技大学前沿科学技术研究院）；Photonics Research Centre, Universiti Malaya（马来亚大学光子研究中心）；Nanophotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge（剑桥大学物理系卡文迪许实验室纳米光子学中心）
Ultrafast Dipolar Electrostatic Modeling of Plasmonic Nanoparticles with Arbitrary Geometry
INESC TEC - Institute of Systems and Computer Engineering, Technology and Science（系统与计算机工程、技术与科学研究所）；Department of Physics, School of Science and Technology, University of Trás-os-Montes e Alto Douro（特拉奥什蒙特和阿尔托杜罗大学理学院物理系）；Department of Physics, Faculty of Sciences, University of Porto（波尔图大学理学院物理系）
The interaction between light and metal nanoparticles enables investigations of microscopic phenomena on nanometer length and ultrashort time scales, benefiting from strong confinement and enhancement of the optical field. However, the ultrafast dynamics of these nanoparticles are primarily investigated by multiphoton photoluminescence on picoseconds or photoemission on femtoseconds independently. Here, we presented two-photon photoluminescence (TPPL) measurements on individual Au nanobipyramids (AuNP) to reveal their ultrafast dynamics by two-pulse excitation on a global time scale ranging fr…
Active nanoplasmonics has recently led to the emergence of many promising applications. One of them is spaser (surface plasmons amplification by stimulated emission of radiation) that has been shown to generate coherent and intense fields of selected surface plasmon modes that are strongly localized in the nanoscale. We propose a novel nanospaser composed of metal nanoparticles-graphene nanodisks hybrid plasmonic system as its resonator and a quantum dots cascade stack as its gain medium. We derive the plasmonic fields induced by pulsed excitation through the use of the effective medium theory…
Bimetallic nanostructures combining plasmonic and catalytic metals are promising for tailoring and enhancing plasmonic hot-carrier generation utilized in plasmonic catalysis. In this work, we study the plasmonic hot-carrier generation in noble metal nanoparticles (Ag, Au, Cu) with single-atom dopants (Ag, Au, Cu, Pd, Pt) with first-principles time-dependent density-functional theory calculations. Our results show that the local hot-carrier generation at the dopant atom is significantly altered by the dopant element while the plasmonic response of the nanoparticle as a whole is not significantl…
High-index dielectric nanoparticles have become a powerful platform for modern light science, enabling various fascinating applications, especially in nonlinear nanophotonics for which they enable special types of optical nonlinearity, such as electron-hole plasma photoexcitation, which are not inherent to plasmonic nanostructures. Here, we propose a novel geometry for highly tunable all-dielectric nanoantennas, consisting of a chain of silicon nanoparticles excited by an electric dipole source, which allows tuning their radiation properties via electron-hole plasma photoexcitation. We show th…
We theoretically study on non-perturbative effective nonlinear responses of metal nanocomposites based on the intrinsic third-order nonlinear response of metal nanoparticles. The large intrinsic third-order nonlinear susceptibility of metal nanoparticles and an irradiation by ultrashort control pulse of light with a sufficiently high peak intensity and moderate fluence can induce a local-field-depression and a saturated plasmon-bleaching in metal nanoparticles. If the control pulse is on, the metal nanocomposites can behave like a dielectric due to the local-field-depression, while if the cont…
Laser-induced transient opacity in helium nanodroplets probed by single-shot coherent diffraction
ETH Zurich（苏黎世联邦理工学院）；University of Rostock（罗斯托克大学）；Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy（马克斯·玻恩非线性光学和超快光谱研究所）；Technical University of Berlin（柏林工业大学）
Ultrafast X-ray imaging provides high resolution information on individual fragile specimens such as aerosols, metastable particles, superfluid quantum systems and live biospecimen, which is inaccessible with conventional imaging techniques. Coherent X-ray diffractive imaging, however, suffers from intrinsic loss of phase, and therefore structure recovery is often complicated and not always uniquely-defined. Here, we introduce the method of in-flight holography, where we use nanoclusters as reference X-ray scatterers in order to encode relative phase information into diffraction patterns of a …
The study of metallic nanoparticles has a long tradition in linear and nonlinear optics [1], with current emphasis on the ultrafast dynamics, size, shape and collective effects in their optical response [2-6]. Nanoparticles also represent the ultimate confined geometry:high surface-to-volume ratios lead to local field enhancements and a range of dramatic modifications of the material's properties and phase diagram [7-9]. Confined gallium has become a subject of special interest as the light-induced structural phase transition recently observed in gallium films [10, 11] has allowed for the demo…
We provide a microscopic approach to describe the onset of radial oscillation of a silver nanoparticle. Using the Heisenberg equation of motion framework, we find that the coupled ultrafast dynamics of coherently excited electron occupation and the coherent phonon amplitude initiate periodic size oscillations of the nanoparticle. Compared to the established interpretation of experiments, our results show a more direct coupling mechanism between the field intensity and coherent phonons. This interaction triggers a size oscillation via an optically induced electron density gradient occurring dir…
Plasmon-mediated superradiance for molecules around metallic nanospheres was proposed ten years ago. However, its demonstration has not been achieved yet due to the experimental difficulty of positioning molecules, and the theoretical limitation to the enhanced collective rate of low excited molecules. In this Letter, we propose that the ultrafast plasmon-mediated superradiant pulses can be observed with strongly excited methylene blue molecules standing vertically inside gold nanoparticle-on-mirror nanocavities. Our simulations indicate that in this system the molecules could interact with ea…
Diffraction-before-destruction imaging with single ultrashort X-ray pulses has the potential to visualise non-equilibrium processes, such as chemical reactions, at the nanoscale with sub-femtosecond resolution in the native environment without the need of crystallization. Here, a nanospecimen partially diffracts a single X-ray flash before sample damage occurs. The structural information of the sample can be reconstructed from the coherent X-ray interference image. State-of-art spatial resolution of such snapshots from individual heavy element nanoparticles is limited to a few nanometers. Furt…
In this work, we observe plasmon induced hot electron extraction in a heterojunction between indium tin oxide nanocrystals and monolayer molybdenum disulphide. We study the sample with ultrafast differential transmission exciting the sample at 1750 nm where the intense localized plasmon surface resonance of the indium tin oxide nanocrystals is and where the monolayer molybdenum disulphide does not absorb light. With the excitation at 1750 nm we observe the excitonic features of molybdenum disulphide in the visible range, close to the exciton of molybdenum disulphide. Such phenomenon can be asc…
Spatio-temporal control of ultrafast plasmon resonances has gained research interest in recent years because of their tremendous implications in nonlinear optics and ultrafast quantum technology. In particular, the lifetime of ultrashort plasmon oscillations has become a debatable subject in recent experimental and theoretical studies to fulfill the future challenges concerning their effective employment in the vast applications of the plasmonic industry. Here, we examined the temporal properties of nonlinear plasmonic modes in metal nanostructures by interacting them with quantum objects in t…
The optical response of materials based on gold nanoparticle assemblies depends on many parameters regarding both material morphology and light excitation characteristics. In this paper, the interplay between the optical and thermal responses of such media is particularly investigated under its theoretical aspect. Both conventional and original modeling approaches are presented and applied to concrete cases. We first show how the interaction of light with matrix-embedded gold nanoparticles can result in the generation of thermal excitations through different energy exchange mechanisms. We then…
High-quality emission centers in two-dimensional materials are promising components for future photonic and optoelectronic applications. Carbon-enriched hexagonal boron nitride (hBN:C) layers host atom-like color-center (CC) defects with strong and robust photoemission up to room temperature. Placing the hBN:C layers on top of Ag triangle nanoparticles (NPs) accelerate the decay of the CC defects down to 46 ps from their reference bulk value of 350 ps. The ultrafast decay is achieved due to the efficient excitation of the plasmon modes of the Ag NPs by the near field of the CCs. Simulations of…
Electromagnetic coupling between subradiant plasmons and dye molecular excitons analyzed by spectral changes in ultrafast surface-enhanced fluorescence
Health and Medical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)（产业技术综合研究所健康与医学研究所）；School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST)（日本高级科学技术研究院材料科学学院）
A recent study shows that: when a long lifetime particle is positioned near a plasmonic metal nanoparticle, lifetime of plasmon oscillations extends, but, "only" near that long-life particle [PRB 101, 035416 (2020)]. Here, we show that this phenomenon can be utilized for ultrahigh (single-molecule) resolution ultrafast apertureless (scattering) SNOM applications. We use the exact solutions of 3D Maxwell equations. We illuminate a metal-coated silicon tip, a quantum emitter (QE) placed on the tip apex, with a femtosecond laser. The induced near-field in the apex decays rapidly except in the vic…
The interaction of swift, free-space electrons with confined optical near fields has recently sparked much interest. It enables a new type of photon-induced near-field electron microscopy, mapping local optical near fields around nanoparticles with exquisite spatial and spectral resolution and lies at the heart of quantum state manipulation and attosecond pulse shaping of free electrons. The corresponding interaction of optical near fields with slow electrons has achieved much less attention, even though the lower electron velocity may enhance electron-near-field coupling for small nanoparticl…
Lasing at the nanometre scale promises strong light-matter interactions and ultrafast operation. Plasmonic resonances supported by metallic nanoparticles have extremely small mode volumes and high field enhancements, making them an ideal platform for studying nanoscale lasing. At visible frequencies, however, the applicability of plasmon resonances is limited due to strong ohmic and radiative losses. Intriguingly, plasmonic nanoparticle arrays support non-radiative dark modes that offer longer life-times but are inaccessible to far-field radiation. Here, we show lasing both in dark and bright …
Helicity-Resolved Spatiotemporal Mapping of Chiral Plexcitons in Helicoids
Seoul National University（首尔大学）；Lund University（隆德大学）；United Arab Emirates University（阿联酋大学）；Korea Research Institute of Standards and Science (KRISS)（韩国标准科学研究院）
