Enhancing the optical excitation efficiency of a single self-assembled quantum dot with a plasmonic nanoantenna
Markus Pfeiffer, Klas Lindfors, Christian Wolpert, Paola Atkinson, Mohamed Benyoucef, Armando Rastelli, Oliver G. Schmidt, Harald Giessen, Markus Lippitz
We demonstrate how the controlled positioning of a plasmonic nanoparticle modifies the photoluminescence of a single epitaxial GaAs quantum dot. The antenna particle leads to an increase of the luminescence intensity by about a factor of eight. Spectrally and temporally resolved photoluminescence measurements prove an increase of the quantum dot's excitation rate. The combination of stable epitaxial quantum emitters and plasmonic nanostructures promises to be highly beneficial for nanoscience and quantum optics.
Nanophotonic (nanoplasmonic) structures confine, guide, and concentrate light on the nanoscale. Advancement of nanophotonics critically depends on active nanoscale control of these phenomena. Localized control of the insulator and metallic phases of vanadium dioxide (VO2) would open up a universe of applications in nanophotonics via modulation of the local dielectric environment of nanophotonic structures allowing them to function as active devices. Here we show dynamic reversible control of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantenn…
We present the simulation, fabrication and optical characterization of plasmonic gold bowtie nanoantennas on a semiconducting GaAs substrate as geometrical parameters such as size, feed gap, height and polarization of the incident light are varied. The surface plasmon resonance was probed using white light reflectivity on an array of nominally identical, 35nm thick Au antennas. To elucidate the influence of the semiconducting, high refractive index substrate, all experiments were compared using nominally identical structures on glass. Besides a linear shift of the surface plasmon resonance fro…
Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g. plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are sup-pressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a s…
A rigorous theory of photon emission accompanied inelastic tunnelling inside the gap of plasmonic nanoantennas has been developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. Resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven nanoplasmonic circuits.
We present a new design of plasmonic nanoantenna with a slant gap for optical chirality engineering. At resonance, the slant gap provides highly enhanced electric field parallel to external magnetic field with a phase delay of 90 degree, resulting in enhanced optical chirality. We show by numerical simulations that upon linearly polarized excitation our achiral nanoantenna can generate near field with enhanced optical chirality that can be tuned by the slant angle and resonance condition. Our design can be easily realized and may find applications in circular dichroism enhancement.
Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding …
Boosting nonlinear frequency conversion in extremely confined volumes remains a key challenge in nano-optics, nanomedicine, photocatalysis, and background-free biosensing. To this aim, field enhancements in plasmonic nanostructures are often exploited to effectively compensate for the lack of phase-matching at the nanoscale. Second harmonic generation (SHG) is, however, strongly quenched by the high degree of symmetry in plasmonic materials at the atomic scale and in nanoantenna designs. Here, we devise a plasmonic nanoantenna lacking axial symmetry, which exhibits spatial and frequency mode o…
We present a practical new method for fabricating a coupled single quantum emitter-plasmonic nanoantenna system. Emission characteristics of a single defect center embedded in hexagonal Boron Nitride (hBN) multilayers is modified using plasmonic nanoantennas. By dewetting thin silver films on hBN multilayers, plasmonic nanoantennas are obtained in a size controlled way with no adverse effects on the defects. A very same single defect center is investigated with and without nanoantenna in order to demonstrate the modification of its emission characteristics. Based on the initial silver film thi…
Plasmonic nanostructures that support surface plasmon (SP) resonance potentially provide a route for the development of nanoengineered nonlinear optical devices. In this work, second-order nonlinear light scattering, specifically sum-frequency generation (SFG) and second-harmonic generation (SHG), from plasmonic nanoantennas is modeled by the boundary element method (BEM). Far-field scattering patterns are compared with the results calculated by the Mie theory to validate the accuracy of the developed nonlinear solver. The SFG from a multi-resonant nanoantenna (MR-NA) and the SHG from a partic…
We present a novel procedure for manipulating the near-field of plasmonic nanoantennas using neural network-controlled laser pulse-shaping. As model systems we numerically studied the spatial distribution of the second harmonic response of L-shaped nanoantennas illuminated by broadband laser pulses. We first show that a trained neural network can be used to predict the relative intensity of the second-harmonic hotspots of the nanoantenna for a given spectral phase and that it can be employed to deterministically switch individual hotspots on and off on sub-diffraction length scale by shaping t…
The performance of plasmonic nanoantenna structures on top of SOI wire waveguides as coherent perfect absorbers for modulators and all-optical switches is explored. The absorption, scattering, reflection and transmission spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by means of 3D finite-difference time-domain simulations for single waves propagating along the waveguide, as well as for standing wave scenarios composed from two counterpropagating waves. The investigated configurations showed losses of roughly 1% and extinction ratios greater than 25 dB for modulator…
Plasmonic nanostructures attract tremendous attention as they confine electromagnetic fields well below the diffraction limit while simultaneously sustaining extreme local field enhancements. To fully exploit these properties, the identification and classification of resonances in such nanostructures is crucial. Recently, a novel figure of merit for resonance classification has been proposed 1 and its applicability was demonstrated mostly to toy model systems. This novel measure, the energy-based plasmonicity index (EPI), characterizes the nature of resonances in molecular nanostructures. The …
Nanoantennas for light enhance light-matter interaction at the nanoscale making them useful in optical communication, sensing, and spectroscopy. So far nanoantenna engineering has been largely based on rules derived from the radio frequency domain which neglect the inertia of free metal electrons at optical frequencies causing phenomena such as complete field penetration, ohmic losses and plasmon resonances. Here we introduce a general and scalable evolutionary algorithm that accounts for topological constrains of the fabrication method and therefore yields unexpected nanoantenna designs exhib…
Electrically-driven optical antennas can serve as compact sources of electromagnetic radiation operating at optical frequencies. In the most widely explored configurations, the radiation is generated by electrons tunneling between metallic parts of the structure when a bias voltage is applied across the tunneling gap. Rather than relying on an inherently inefficient inelastic light emission in the gap, we suggest to use a ballistic nanoconstriction as the feed element of an optical antenna supporting plasmonic modes. We discuss the underlying mechanisms responsible for the optical emission, an…
Metal nanostructures are key elements in nanooptics owing to their strong resonant interaction with light through local plasmonic charge oscillations. Their ability to shape light at the nanoscale have made them important across a multitude of areas, including biosensing, energy conversion and ultrathin flat metaoptics. Yet another dimension of avenues is foreseen for dynamic nanoantennas, ranging from tuneable metalenses for miniaturized medical devices to adaptable windows that control radiation flows in and out of buildings. However, enabling nano-optical antennas to be dynamically controll…
The optimization of nonlinear optical processes at the nanoscale is a crucial step for the development of nanoscale photon sources for quantum-optical networks. The development of innovative plasmonic nanoantenna designs and hybrid nanostructures to enhance optical nonlinearities in very small volumes represents one of the most promising routes. In such systems, the upconversion of photons can be achieved with high efficiencies via third-order processes, such as third harmonic generation (THG), thanks to the resonantly-enhanced volume currents. Conversely, second-order processes, such as secon…
Orbital angular momentum of light has recently been recognized as a new degree of freedom to encode information in quantum communication using light pulses. Methods to extract this information include reversing the process by which such twisted light was created in the first place or interference with other beams. Here, we propose an alternative new way to directly read out the extra information encoded in twisted light using plasmonic nanoantennas by con- verting the information about the orbital angular momentum of light into spectral information using bright and dark modes. Exemplarily cons…
Thermonanophotonics, i.e. the study of photothermal effects in optical nanoantennas, has recently attracted growing interest. While thermoplasmonic structures enable a broad range of applications, from imaging and optofluidics devices to medical and photochemical systems, dielectric nanoantennas open new opportunities for thermo-optical modulation and reconfigurable metasurfaces. However, computing both photo-thermal and thermo-optical effects in large arrays of nanoantennas remains a challenge. In this work, we implement a fast numerical method to compute the temperature increase of multi-dim…
Using large-scale, real-time quantum dynamics calculations, we present a detailed analysis of electronic excitation transfer (EET) mechanisms in a multi-particle plasmonic nanoantenna system. Specifically, we utilize real-time, time-dependent, density functional tight binding (RT-TDDFTB) to provide a quantum-mechanical description (at an electronic/atomistic level of detail) for characterizing and analyzing these systems, without recourse to classical approximations. We also demonstrate highly long-range electronic couplings in these complex systems and find that the range of these couplings i…
Nanostructures of conventional metals offer manipulation of light at the nanoscale but are limited to static behavior due to their fixed material properties. To develop the next frontier of dynamic nanooptics and metasurfaces, we utilize the redox-tunable optical properties of conducting polymers, which were recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Using nanodisks of poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system, we present the first electrically tunable conducting polymer nanooptical antennas. In addition to repeate…
The nonlinear process of second harmonic generation (SHG) in monolayer (1L) transition metal dichalcogenides (TMD), like $WS_2$, strongly depends on the polarization state of the excitation light. Combining plasmonic nanostructures with $1L-WS_2$ by transferring it onto a plasmonic nanoantenna array, a hybrid metasurface is realized impacting the polarization dependency of its SHG. Here, we investigate how plasmonic dipole resonances affect the process of SHG in plasmonic-TMD hybrid metasurfaces by nonlinear spectroscopy. We show, that the polarization dependency is affected by the lattice str…
We present numerical studies, nano-fabrication and optical characterization of bowtie nanoantennas demonstrating their superior performance with respect to the electric field enhancement as compared to other Au nanoparticle shapes. For optimized parameters, we found mean intensity enhancement factors >2300x in the feed-gap of the antenna, decreasing to 1300x when introducing a 5nm titanium adhesion layer. Using electron beam lithography we fabricated gold bowties on various substrates with feed-gaps and tip radii as small as 10nm. In polarization resolved measurement we experimentally observed…
We present the experimental realization of ordered arrays of hyper-doped silicon nanodisks, which exhibit a localized surface plasmon resonance. The plasmon is widely tunable in a spectral window between 2 and 5 $μ$m by adjusting the free carrier concentration between 10$^{20}$ and 10$^{21}$ cm$^{-3}$. We show that strong infrared light absorption can be achieved with all-silicon plasmonic metasurfaces employing nano-structures with dimensions as low as 100\,nm in diameter and 23 nm in height. Our numerical simulations show an excellent agreement with the experimental data and provide physical…
We demonstrate third harmonic generation in plasmonic antennas made of highly doped germanium and designed to be resonant in the mid infrared. Owing to the near-field enhancement, the result is an ultrafast, sub-diffraction, coherent light source tunable between 3 and 5 micrometer wavelength on a silicon substrate. To observe nonlinearity in this challenging spectral region, a high-power femtosecond laser system equipped with parametric frequency conversion in combination with an all-reflective confocal microscope setup is employed. We show spatially resolved maps of the linear scattering cros…
We study plasmonic excitations in the limit of few electrons, in one-atom thick sodium chains, and characterize them based on collectivity. We also compare the excitations to classical localised plasmon modes and find for the longitudinal mode a quantum-classical transition around 10 atoms. The transverse mode appears at much higher energies than predicted classically for all chain lengths. The electric field enhancement is also considered which is made possible by considering the effects of electron-phonon coupling on the broadening of the electronic spectra. Large field enhancements are poss…
Light localization is controlled at a scale of lambda/10 in the harmonic regime from the far field domain in a plasmonic nanoantenna. The nanoantenna under study consists of 3 aligned spheres 50 nm in diameter separated by a distance of 5 nm. By simply tuning the orientation of an incident plane wave, symmetric and antisymmetric mode-balancing induces a strong enhancement of the near field intensity in one cavity while nullifying the light intensity in the other cavity. Furthermore, it is demonstrated that the dipolar moment of a plasmonic particle can be fully extinguished when strongly coupl…
Active control of light-matter interactions in semiconductors is critical for realizing next generation optoelectronic devices, with tunable control of the systems optical properties via external fields. The ability to manipulate optical interactions in active materials coupled to cavities via geometrical parameters, which are fixed along with dynamic control with applied fields opens up possibilities of controlling exciton lifetimes, oscillator strengths and their relaxation properties. Here, we demonstrate electrical control of exciton-plasmon polariton coupling strength of a two-dimensional…
We design a photonic sphere-array nanoantenna (NA) exhibiting both strong directionality and wavelength selectivity. Although the geometric configuration of the photonic NA resembles a plasmonic Yagi-Uda NA, it has different working principles, and most importantly, reduces the inherent metallic loss from plasmonic elements. For any selected optical wavelength, a sharp Fano-resonance by the reflector is tunable to overlap spectrally with a wider dipole resonance by the sphere-chain director leading to the high directionality. The work provides design principles for directional and selective ph…
Intermixed light-matter quasiparticles - polaritons - possess unique optical properties owned to their compositional nature. These intriguing hybrid states have been extensively studied over the past decades in a wide range of realizations aiming at both basic science and emerging applications. However, recently it has been demonstrated that not only optical, but also material-related properties, such as chemical reactivity and charge transport, may be significantly altered in the strong coupling regime of light-matter interactions. Here, we show that a nanoscale system, comprised of a plasmon…
The unique gate-voltage dependent optical properties of graphene make it a promising electrically-tunable plasmonic material. In this work, we proposed in-situ control of the polarization of nanoantennas by combining plasmonic structures with an electrostatically tunable graphene monolayer. The tunable polarizer is designed based on an asymmetric cross nanoantenna comprising two orthogonal metallic dipoles sharing the same feed gap. Graphene monolayer is deposited on a Si/SiO2 substrate, and inserted beneath the nanoantenna. Our modelling demonstrates that as the chemical potential is incremen…
Deterministically integrating semiconductor quantum emitters with plasmonic nano-devices paves the way towards chip-scale integrable, true nanoscale quantum photonics technologies. For this purpose, stable and bright semiconductor emitters are needed, which moreover allow for CMOS-compatibility and optical activity in the telecommunication band. Here, we demonstrate strongly enhanced light-matter coupling of single near-surface ($<10\,nm$) InAs quantum dots monolithically integrated into electromagnetic hot-spots of sub-wavelength sized metal nanoantennas. The antenna strongly enhances the emi…
We demonstrate inverse design of plasmonic nanoantennas for directional light scattering. Our method is based on a combination of full-field electrodynamical simulations via the Green dyadic method and evolutionary optimization (EO). Without any initial bias, we find that the geometries reproducibly found by EO, work on the same principles as radio-frequency antennas. We demonstrate the versatility of our approach by designing various directional optical antennas for different scattering problems. EO based nanoantenna design has tremendous potential for a multitude of applications like nano-sc…
We suggest a hybrid plasmonic device consisting of a bimodal metallic nanoantenna coupled to an incoherently pumped quantum emitter. This hybrid device emits light into the two modes entangled in the number of photons. The process is a prime example where losses are turned from a nuisance into something beneficial, since, even though counterintuitively, the entanglement is enabled by strong incoherent processes, i.e. dominant scattering and absorption rates of the nanoantenna. Both, the high emission rate and the degree of entanglement of the emitted light are insensitive with respect to imper…
Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-ofstates engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of optical antennas based on the background of both we…
Planar chiral nanoantenna for excitation-chirality-controlled hot spot modulation and emitter-coupled circularly polarized emission
Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学）；Abbe Center of Photonics, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学阿贝光学中心）；Leibniz Institute of Photonic Technology（莱布尼茨光子技术研究所）；University of Würzburg（维尔茨堡大学）；The Australian National University（澳大利亚国立大学）；Academia Sinica（中央研究院）；National Yang Ming Chiao Tung University（国立阳明交通大学）
The chiral state of a molecule plays a crucial role in molecular recognition and biochemical reactions. Because of this and owing to the fact that most modern drugs are chiral, the sensitive and reliable detection of the chirality of molecules is of great interest to drug development. The majority of naturally occurring biomolecules exhibit circular dichroism (CD) in the UV-range. Theoretical studies and several experiments have demonstrated that this UV-CD can be transferred into the plasmonic frequency domain when metal surfaces and chiral biomolecules are in close proximity. Here, we demons…
The magneto-optical activity, namely the polarization conversion capabilities of high-index, non-absorbing, core-shell dielectric nanospheres is theoretically analyzed. We show that, in analogy with their plasmonic counterparts, the polarization conversion in resonant dielectric particles is linked to the amount of electromagnetic field probing the magneto-optical material in the system. However, in strong contrast with plasmon nanoparticles, due to the peculiar distribution of the internal fields in resonant dielectric spheres, the magneto-optical response is fully governed by the magnetic (d…
We suggest a novel concept of efficient light-trapping structures for thin-film solar cells based on arrays of planar nanoantennas operating far from plasmonic resonances. The operation principle of our structures relies on the excitation of chessboard-like collective modes of the nanoantenna arrays with the field localized between the neighboring metal elements. We demonstrated theoretically substantial enhancement of solar-cell short-circuit current by the designed light-trapping structure in the whole spectrum range of the solar-cell operation compared to conventional structures employing a…
The temperature increase and temperature gradients induced by mid-infrared laser illumination of vertical gold nanoantenna arrays embedded into polymer layers was measured directly with a photothermal expansion nanoscope. Nanoscale thermal hotspot images and local temperature increase spectra were both obtained, the latter by broadly tuning the emission wavelength of a quantum cascade laser. The spectral analysis indicates that plasmon-enhanced mid-infrared vibrations of molecules located in the antenna hotspots are responsible for some of the thermoplasmonic resonances, while Joule heating in…
We report on the structural and optical properties of individual bowtie nanoantennas both on glass and semiconducting GaAs substrates. The antennas on glass (GaAs) are shown to be of excellent quality and high uniformity reflected by narrow size distributions with standard deviations for the triangle and gap size of $σ_s^{glass}=4.5nm$ ($σ_s^{GaAs}=2.6nm$) and $σ_g^{glass}=5.4nm$ ($σ_g^{GaAs}=3.8nm$), respectively. The corresponding optical properties of individual nanoantennas studied by differential reflection spectroscopy show a strong reduction of the localised surface plasmon polariton re…
Optical-field emission from nanostructured solids such as subwavelength nanoantennas can be leveraged to create sub-femtosecond, PHz-scale electronics for optical-field detection. One application that is of particular interest is the detection of an incident optical pulse's carrier-envelope phase. Such carrier-envelope-phase detection requires few-cycle, broadband optical excitation where the resonant properties of the nanoantenna can strongly alter the response of the near field in time. Little quantitative investigation has been performed to understand how the geometry and resonant propertie…
Plasmonic detectors have the potential to provide a method of rapid spectroscopy without the need of moving mirrors or gratings. Previous measurements have demonstrated frequency tunable detection based on plasmonic excitations, however these devices were either small area, polarization dependent and/or required e-beam lithography. We demonstrate that large area high sensitivity THz plasmonic detection can be achieved using self-assembly nanosphere lithography. We achieve a submicron feature size grid covering a detector area of 4 mm^2. The absorbance at the fundamental, third and 5th harmonic…
Nanoplasmonic systems combined with optically-active two-dimensional materials provide intriguing opportunities to explore and control light-matter interactions at extreme sub-wavelength lengthscales approaching the exciton Bohr radius. Here, we present room- and cryogenic-temperature investigations of light-matter interactions between an MoSe$_2$ monolayer and individual lithographically defined gold dipole nanoantennas having sub-10 nm feed gaps. By progressively tuning the nanoantenna size, their dipolar resonance is tuned relative to the A-exciton transition in a proximal MoSe$_2$ monolaye…
Films of close-packed Au nanoparticles are coupled electrodynamically through their collective plasmon resonances. This collective optical response results in enhanced light-matter interactions, which can be exploited in various applications. Here, we demonstrate their application in sensing volatile organic compounds, using methanol as a test-case. Ordered films over several cm2 were obtained by interfacial self-assembly of colloidal Au nanoparticles (~10 nm diameter) through controlled evaporation of the solvent. Even though isolated nanoparticles of this size are inherently non-scattering, …
Molecular chirality plays a crucial role in innumerable biological processes. The chirality of a molecule can typically be identified by its characteristic optical response, the circular dichroism (CD). CD signals have thus long been used to identify the state of molecules or to follow dynamic protein configurations. In recent years, the focus has moved towards plasmonic nanostructures, as they show potential for applications ranging from pathogen sensing to novel optical materials. The plasmonic coupling of the individual elements of such chiral metallic structures is a crucial prerequisite t…
