Publications
187 results found
Grinblat G, Berte R, Nielsen MP, et al., 2018, Sub-20 fs all-optical switching in a single Au-Clad Si nanodisk, Nano Letters, Vol: 18, Pages: 7896-7900, ISSN: 1530-6984
Dielectric nanoantennas have recently emerged as promising elements for nonlinear and ultrafast nanophotonics due to their ability to concentrate light on the nanometer scale with low losses, while exhibiting large nonlinear susceptibilities. In this work, we demonstrate that single Si nanodisks covered with a thin 30 nm thick layer of Au can generate positive and negative sub-20 fs reflectivity modulations of ∼0.3% in the vicinity of the first-order anapole mode, when excited around the second-order anapole mode. The experimental results, characterized in the visible to near-infrared spectral range, suggest that the nonlinear optical Kerr effect is the responsible mechanism for the observed all-optical switching phenomena. These findings represent an important step toward nanoscale ultrafast all-optical signal processing.
Shautsova V, Sidiropoulos T, Xiao X, et al., 2018, Plasmon induced thermoelectric effect in graphene, Nature Communications, Vol: 9, ISSN: 2041-1723
Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.
Gusken N, Nielsen M, Nguyen N, et al., 2018, Nanofocusing in SOI-based hybrid plasmonic metal slot waveguides, Optics Express, Vol: 26, Pages: 30634-30643, ISSN: 1094-4087
Abstract: Through a process of efficient dielectric to metallic waveguide mode conversion, we calculate a >400-fold field intensity enhancement in a silicon photonics compatible nanofocusing device. A metallic slot waveguide sits on top of the silicon slab waveguide with nanofocusing being achieved by tapering the slot width gradually. We evaluate the conversion between the numerous photonic modes of the planar silicon waveguide slab and the most confined plasmonic mode of a 20 x 50 nm2 slot in the metallic film. With an efficiency of ~80%, this system enables remarkably effective nanofocusing, although the small amount of inter-mode coupling shows that this structure is not quite adiabatic. In order to couple photonic and plasmonic modes efficiently, in-plane focusing is required, simulated here by curved input grating couplers. The nanofocusing device shows how to efficiently bridge the photonic micro-regime and the plasmonic nano-regime whilst maintaining compatibility with the silicon photonics platform.
Kumar R, Verzhbitskiy I, Giustiniano F, et al., 2018, Interlayer screening effects in WS2/WSe2 van der Waals hetero-bilayer, 2D MATERIALS, Vol: 5, ISSN: 2053-1583
Gennaro SD, Li Y, Maier SA, et al., 2018, Double blind ultrafast pulse characterization by mixed frequency generation in a gold antenna, ACS Photonics, Vol: 5, Pages: 3166-3171, ISSN: 2330-4022
Ultrafast pulse characterization requires the analysis of correlation functions generated by frequency mixing of optical pulses in a nonlinear medium. In this work, we use a gold optical nanoantenna to generate simultaneously Four Wave Mixing and Sum Frequency Generation across the tuning range of a Ti: Sapphire and Optical Parametric Oscillator (OPO) system. Since metal nanoparticles create remarkably strong nonlinear responses for their size without the need for phase matching, this allows us to simultaneously characterize the unknown OPO pulse and its pump pulse using a single spectrogram. The nonlinear mixing is efficient enough to retrieve pulses with energies in the picojoule range.
Wells M, Bower R, Kilmurray B, et al., 2018, Temperature stability of thin film refractory plasmonic materials, Optics Express, Vol: 12, Pages: 15726-15744, ISSN: 1094-4087
Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their stability at high operational temperatures. However, investigation of the reproducibility of the optical properties after thermal cycling between room and elevated temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, SrRuO3 and SrNbO3 are investigated to assess their viability for robust refractory plasmonic applications. These results are further compared to the performance of SrMoO3 reported in literature. Films ranging in thickness from 50 to 105 nm are deposited on MgO, SrTiO3 and Si substrates by e-beam evaporation, RF magnetron sputtering and pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 to 1000° C for one hour, to establish the maximum cycling temperature and potential longevity at elevated temperatures for each material. It is found that SrRuO3 retains metallic behaviour after annealing at 800° C, while SrNbO3 undergoes a phase transition resulting in a loss of metallic behaviour after annealing at 400° C. Importantly, the optical properties of TiN and TiON are degraded as a result of oxidation and show a loss of metallic behaviour after annealing at 500° C, while the same is not observed in Au until annealing at 600° C. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.
Matsui T, Li Y, Hsu M-HM, et al., 2018, Highly Stable Plasmon Induced Hot Hole Transfer into Silicon via a SrTiO3 Passivation Interface, ADVANCED FUNCTIONAL MATERIALS, Vol: 28, ISSN: 1616-301X
Extracting plasmon‐induced hot carriers over a metal–semiconductor Schottky barrier enables photodetection below the semiconductor bandgap energy. However, interfacial carrier recombination hinders the efficiency and stability of this process, severely limiting its implementation in telecommunication. This study proposes and demonstrates the use of epitaxially grown lattice‐matched SrTiO3 for interfacial passivation of silicon‐based plasmonic Schottky devices. The devices are activated by an electrical soft‐breakdown of the interfacial SrTiO3 layer, resulting in reproducible rectified Schottky characteristics. The transition to a low resistance state of the SrTiO3 layer boosts the extraction efficiency of hot holes upon resonant plasmonic excitation, giving rise to a two orders of magnitude higher photocurrent compared to devices with a native oxide layer. Photoresponse, tunability, and barrier height studies under reverse biases as high as 100 V present superior stability with the incorporation of the SrTiO3 layer. The investigation paves the way toward plasmon‐induced photodetection for practical applications including those under challenging operating conditions.
Mignuzzi S, Mota M, Coenen T, et al., 2018, Energy-momentum cathodoluminescence spectroscopy of dielectric nanostructures, ACS Photonics, Vol: 5, Pages: 1381-1387, ISSN: 2330-4022
Precise knowledge of the local density of optical states (LDOS) is fundamental to understanding nanophotonic systems and devices. Complete LDOS mapping requires resolution in energy, momentum, and space, and hence a versatile measurement approach capable of providing simultaneous access to the LDOS components is highly desirable. Here, we explore a modality of cathodoluminescence spectroscopy able to resolve, in single acquisitions, the dispersion in energy and momentum of the radiative LDOS. We perform measurements on a titanium nitride diffraction grating, bulk molybdenum disulfide, and silicon to demonstrate that the technique can probe and disentangle the dispersion of coherent and incoherent cathodoluminescence signals. The approach presented raises cathodoluminescence spectroscopy to a versatile tool for subwavelength design and optimization of nanophotonic devices in the reciprocal space.
Nielsen MP, Nicholas, Gusken, et al., 2018, Giant nonlinear response at a plasmonic nanofocus drives efficient four wave mixing over micron length scales
We demonstrate four wave mixing in an integrated plasmonic gap waveguide on silicon that strongly confines light within a nonlinear organic polymer. We report >1% signal to idler conversion efficiency over micron-scale interaction lengths.
München, Matsui T, Li Y, et al., 2018, Plasmonic hot carrier detection via SrTiO<inf>3</inf> interfacial layer
Energetic hot carrier injection from metal plasmonic structure to adjacent semiconductor lies at the center of the application of non-radiative decays, photochemical reactions and energy harvesting. Plasmonic hot-electron devices, till now, have been highly focused on a Schottky barrier structures to separate the energetic carriers before the thermalization. For instance, much efforts were putted in exploring high absorption structure with enough thin metal; enough thin compared to mean free path. However, interfacial engineering of the device; exploring a new device structure, have not been fully investigated.
Rahmani M, Leo G, Brener I, et al., 2018, Nonlinear frequency conversion in optical nanoantennas and metasurfaces: materials evolution and fabrication, OPTO-ELECTRONIC ADVANCES, Vol: 1
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Wang S, Wang X-Y, Li B, et al., 2018, Unusual Scaling Laws for Plasmonic Nanolasers, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Nguyen NB, Nielsen MP, Lafone L, et al., 2017, Hybrid gap plasmon GaAs nanolasers, APPLIED PHYSICS LETTERS, Vol: 111, ISSN: 0003-6951
Nielsen MP, Shi X, Dichtl P, et al., 2017, Giant nonlinear response at a plasmonic nanofocus drives efficient four-wave mixing, Science, Vol: 358, Pages: 1179-1181, ISSN: 0036-8075
Efficient optical frequency mixing typically must accumulate over large interaction lengths because nonlinear responses in natural materials are inherently weak. This limits the efficiency of mixing processes owing to the requirement of phase matching. Here, we report efficient four-wave mixing (FWM) over micrometer-scale interaction lengths at telecommunications wavelengths on silicon. We used an integrated plasmonic gap waveguide that strongly confines light within a nonlinear organic polymer. The gap waveguide intensifies light by nanofocusing it to a mode cross-section of a few tens of nanometers, thus generating a nonlinear response so strong that efficient FWM accumulates over wavelength-scale distances. This technique opens up nonlinear optics to a regime of relaxed phase matching, with the possibility of compact, broadband, and efficient frequency mixing integrated with silicon photonics.
Wang S, Wang X-Y, Li B, et al., 2017, Unusual scaling laws for plasmonic nanolasers beyond the diffraction limit., Nature Communications, Vol: 8, ISSN: 2041-1723
Plasmonic nanolasers are a new class of amplifiers that generate coherent light well below the diffraction barrier bringing fundamentally new capabilities to biochemical sensing, super-resolution imaging, and on-chip optical communication. However, a debate about whether metals can enhance the performance of lasers has persisted due to the unavoidable fact that metallic absorption intrinsically scales with field confinement. Here, we report plasmonic nanolasers with extremely low thresholds on the order of 10 kW cm-2 at room temperature, which are comparable to those found in modern laser diodes. More importantly, we find unusual scaling laws allowing plasmonic lasers to be more compact and faster with lower threshold and power consumption than photonic lasers when the cavity size approaches or surpasses the diffraction limit. This clarifies the long-standing debate over the viability of metal confinement and feedback strategies in laser technology and identifies situations where plasmonic lasers can have clear practical advantage.
Wells MP, Zou B, Doiron BG, et al., 2017, Tunable, Low Optical Loss Strontium Molybdate Thin Films for Plasmonic Applications, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071
Strontium molybdate (SrMoO3) thin films are grown epitaxially on strontium titanate (SrTiO3), magnesium oxide (MgO), and lanthanum aluminate (LaAlO3) substrates by pulsed laser deposition and possess electrical resistivity as low as 100 µΩ cm at room temperature. SrMoO3 is shown to have optical losses, characterized by the product of the Drude broadening, ΓD, and the square of the plasma frequency, ωpu2, significantly lower than TiN, though generally higher than Au. Also, it is demonstrated that there is a zero-crossover wavelength of the real part of the dielectric permittivity, which is between 600 and 950 nm (2.05 and 1.31 eV), as measured by spectroscopic ellipsometry. Moreover, the epsilon near zero (ENZ) wavelength can be controlled by engineering the residual strain in the films, which arises from a strain dependence of the charge carrier concentration, as confirmed by density of states calculations. The relatively broad tunability of ENZ behavior observed in SrMoO3 demonstrates its potential suitability for transformation optics along with plasmonic applications in the visible to near infrared spectral range.
Grinblat G, Li Y, Nielsen MP, et al., 2017, Degenerate four-wave mixing in a multiresonant Germanium nanodisk, ACS Photonics, Vol: 4, Pages: 2144-2149, ISSN: 2330-4022
Dielectric nanoantennas excited at Mie resonances are becoming suitable candidates for nonlinear optical effects due to their large intrinsic nonlinearity and capability to highly confine electromagnetic fields within subwavelength volumes. In this work, we show that a single Ge nanodisk, recently demonstrated as an efficient source of third-harmonic generation (THG), can also be exploited for four-wave mixing (FWM) phenomena. The high field enhancement inside the disk yields effective third-order susceptibilities as high as 2 × 10–8 esu (2.8 × 10–16 m2/V2), which were determined by single pump wavelength THG measurements tuned to high-order Mie modes. A similar nonlinear optical response is observed in the case of degenerate FWM where two different pump wavelengths are coupled to a single high-order resonant mode. However, when the two pump wavelengths are coupled to different high-order modes, the FWM process is partially suppressed due to a diminished near-field spatial overlap of the mixed wavelengths within the disk. This investigation reveals useful pathways for the optimization of third-order optical processes in all-dielectric nanostructures.
Doiron B, Li Y, Mihai AP, et al., 2017, Comparison of the ultrafast hot electron dynamics of titanium nitride and gold for plasmonic applications, SPIE Optics + Photonics Conference on Plasmonics - Design, Materials, Fabrication, Characterization, and Applications XV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
With similar optical properties to gold and high thermal stability, titanium nitride continues to prove itself as a promising plasmonic material for high-temperature applications in the visible and near-infrared. In this work, we use transient pump probe differential reflection measurements to compare the electron energy decay channels in titanium nitride and gold thin films. Using an extended two temperature model to incorporate the photoexcited electrons, it is possible to separate the electron-electron and electron-phonon scattering contributions immediately following the arrival of the pump pulse. This model allows for incredibly accurate determination of the internal electronic properties using only optical measurements. As the electronic properties are key in hot electron applications, we show that titanium nitide has substantially longer electron thermalization and electron-phonon scattering times. With this, we were also able to resolve electron thermal conduction in the film using purely optical measurements.
Braic L, Vasilantonakis N, Mihai A, et al., 2017, Titanium oxynitride thin films with tuneable double epsilon-near-zero behaviour for nanophotonic applications, ACS Applied Materials and Interfaces, Vol: 9, Pages: 29857-29862, ISSN: 1944-8244
Titanium oxynitride (TiOxNy) thin films are fabricated using reactive magnetron sputtering. The mechanism of their growth formation is explained, and their optical properties are presented. The films grown when the level of residual oxygen in the background vacuum was between 5 nTorr to 20 nTorr exhibit double epsilon-near-Zero (2-ENZ) behavior with ENZ1 and ENZ2 wavelengths tunable in the 700–850 and 1100–1350 nm spectral ranges, respectively. Samples fabricated when the level of residual oxygen in the background vacuum was above 2 × 10–8 Torr exhibit nonmetallic behavior, while the layers deposited when the level of residual oxygen in the background vacuum was below 5 × 10–9 Torr show metallic behavior with a single ENZ value. The double ENZ phenomenon is related to the level of residual oxygen in the background vacuum and is attributed to the mixture of TiN and TiOxNy and TiOx phases in the films. Varying the partial pressure of nitrogen during the deposition can further control the amount of TiN, TiOx, and TiOxNy compounds in the films and, therefore, tune the screened plasma wavelengths. A good approximation of the ellipsometric behavior is achieved with Maxwell–Garnett theory for a composite film formed by a mixture of TiO2 and TiN phases suggesting that double ENZ TiOxNy films are formed by inclusions of TiN within a TiO2 matrix. These oxynitride compounds could be considered as new materials exhibiting double ENZ in the visible and near-IR spectral ranges. Materials with ENZ properties are advantageous for designing the enhanced nonlinear optical response, metasurfaces, and nonreciprocal behavior.
Yu H, Sidiropoulos T, Liu W, et al., 2017, Influence of silver film quality on the threshold of plasmonic nanowire lasers, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071
Plasmonic nanowire lasers are nanoscopic sources of light operating at deep subwavelength scales with ultrafast dynamics.[1-6] Such lasers enable the investigation of enhanced light-matter interactions and can have large impact on applications in the fields of non-linear optics, sensing, and optical communications.[7-12] However, metal-based lasers suffer from high losses, caused by the inherent electron scattering in metals, which leads to an increased lasing threshold and limits their use in applications. To minimise losses and thus improve their performance, it has been suggested to use metal films of high quality which ideally have an ultra-flat surface with a high crystalline perfection.[1, 13-16] However, investigating the effects of Ag film quality on the performance of hybrid-plasmonic zinc oxide (ZnO) nanowire lasers this work finds that such a laser geometry is dominated by losses in the gain material.
Ngoc BN, Maier SA, Hong M, et al., 2017, Erratum: Recovering parity-time symmetry in highly dispersive coupled optical waveguides (vol 18, 125012, 2016), New Journal of Physics, Vol: 19, ISSN: 1367-2630
Coupled photonic systems satisfying parity-time symmetry (PTS) provide exibility to engineer the ow of light including non-reciprocal propagation, perfect laser-absorbers, and ultra-fast switching. Achieving the required index pro le for an optical system with ideal PTS, i.e. n(x) =n(-x)*, has proven to be difficult due to the challenge of controlling gain, loss and material dispersion simultaneously. Consequently, most research has focused on dilute or low gain optical systems where material dispersion is minimal. In this paper, we study a model system of coupled inorganic semiconductor waveguides with potentially high gain (>1,500 cm-1) and dispersion. Our analysis makes use of coupled mode theory's parameters to quantify smooth transitions between PTS phases under imperfect conditions. We find that the detrimental influence of gain-induced dispersion is counteracted and the key features of parity-time symmetric optical systems are recovered by working with non-identical waveguides and bias pumping of the optical waveguides. Our coupled mode theory results show excellent agreement with numerical solutions, proving the robustness of coupled mode theory in describing various degrees of imperfection in systems with PTS.
Nguyen N, Maier SA, Hong M, et al., 2016, Recovering parity-time symmetry in highly dispersive coupled optical waveguides, New Journal of Physics, Vol: 18, ISSN: 1367-2630
Coupled photonic systems satisfying parity-time symmetry (PTS) provideexibility to engineer the ow of light including non-reciprocal propagation, perfectlaser-absorbers, and ultra-fast switching. Achieving the required index pro le foran optical system with ideal PTS, i.e. n(x) =n(-x)*, has proven to be difficult due to the challenge of controlling gain, loss and material dispersion simultaneously. Consequently, most research has focused on dilute or low gain optical systems where material dispersion is minimal. In this paper, we study a model system of coupled inorganic semiconductor waveguides with potentially high gain (>1,500 cm-1) and dispersion. Our analysis makes use of coupled mode theory's parameters to quantify smooth transitions between PTS phases under imperfect conditions. We find that the detrimental influence of gain-induced dispersion is counteracted and the key features of parity-time symmetric optical systems are recovered by working with non-identical waveguides and bias pumping of the optical waveguides. Our coupled mode theory results show excellent agreement with numerical solutions, proving the robustness of coupled mode theory in describing various degrees of imperfection in systems with PTS.
Yu H, Ren K, Wu Q, et al., 2016, Organic-inorganic perovskite plasmonic nanowire lasers with a low threshold and a good thermal stability, Nanoscale, Vol: 8, Pages: 19536-19540, ISSN: 2040-3364
Plasmonic nanolasers have ushered in a paradigm of deep sub-wavelength coherent optical sources with ultrafast dynamics that exploit the strong confinement capabilities of metals. Although these devices are usually associated with higher thresholds due to absorption in metals, the high gain inorganic II–VI and III–V semiconductor materials have allowed the realization of plasmonic nanolasers operating under ambient conditions. In this work, we introduce single-crystalline lead halide perovskite (CH3NH3PbI3) nanowires as an organic–inorganic semiconducting gain material to the plasmonic laser community. We demonstrate plasmonic laser action using a hybrid geometry whereby the perovskite nanowires are placed on a silver substrate with an insulating spacer layer. We report relatively low threshold operation under ambient conditions (13.5 μJ cm−2), and the devices work well even at temperatures up to 43.6 °C. The demonstration highlights the high optical gain achievable in perovskite materials and thus provides a solution to high gain materials for plasmonic devices.
Grinblat G, Li Y, Nielsen MP, et al., 2016, Efficient third harmonic generation and nonlinear subwavelength imaging at a higher-order anapole mode in a single germanium nanodisk., ACS Nano, Vol: 11, Pages: 953-960
Benefiting from large intrinsic nonlinearities, low absorption, and high field enhancement abilities, all-dielectric nanoantennas are considered essential for efficient nonlinear processes at subwavelength volumes. In particular, when the dielectric nanoantenna supports the nonradiating anapole mode, characterized by a minimum in the extinction cross section and a maximum electric energy within the material, third harmonic generation (THG) processes can be greatly enhanced. In this work, we demonstrate that a higher-order anapole mode in a 200 nm thick germanium nanodisk delivers the highest THG efficiency on the nanoscale at optical frequencies. By doubling the diameter of a disk supporting the fundamental anapole mode, we discover the emergence of an anapole mode of higher order, with a valley in the extinction cross section significantly narrower than that of the fundamental anapole. Under this condition, we observe a highly improved electric field confinement effect within the dielectric disk, leading to THG conversion efficiencies as large as 0.001% at a third harmonic wavelength of 550 nm. In addition, by mapping the THG emission across the nanodisk, we are able to unveil the anapole near-field intensity distributions, which show excellent agreement with numerical simulations. Our findings remarkably expand contemporary knowledge on localized modes in dielectric nanosystems, revealing crucial elements for the elaboration of highly efficient frequency upconversion nanodevices.
Gennaro SD, Rahmani M, Giannini V, et al., 2016, The interplay of symmetry and scattering phase in second harmonic generation from gold nanoantennas, Nano Letters, Vol: 16, Pages: 5278-5285, ISSN: 1530-6992
Nonlinear phenomena are central to modern photonics but, being inherently weak, typically require gradual accumulation over several millimeters. For example, second harmonic generation (SHG) is typically achieved in thick transparent nonlinear crystals by phase-matching energy exchange between light at initial, ω, and final, 2ω, frequencies. Recently, metamaterials imbued with artificial nonlinearity from their constituent nanoantennas have generated excitement by opening the possibility of wavelength-scale nonlinear optics. However, the selection rules of SHG typically prevent dipole emission from simple nanoantennas, which has led to much discussion concerning the best geometries, for example, those breaking centro-symmetry or incorporating resonances at multiple harmonics. In this work, we explore the use of both nanoantenna symmetry and multiple harmonics to control the strength, polarization and radiation pattern of SHG from a variety of antenna configurations incorporating simple resonant elements tuned to light at both ω and 2ω. We use a microscopic description of the scattering strength and phases of these constituent particles, determined by their relative positions, to accurately predict the SHG radiation observed in our experiments. We find that the 2ω particles radiate dipolar SHG by near-field coupling to the ω particle, which radiates SHG as a quadrupole. Consequently, strong linearly polarized dipolar SHG is only possible for noncentro-symmetric antennas that also minimize interference between their dipolar and quadrupolar responses. Metamaterials with such intra-antenna phase and polarization control could enable compact nonlinear photonic nanotechnologies.
Grinblat G, Li Y, Nielsen MP, et al., 2016, Enhanced third harmonic generation in single Germanium nanodisks excited at the anapole mode, Nano Letters, Vol: 16, Pages: 4635-4640, ISSN: 1530-6992
We present an all-dielectric germanium nanosystem exhibiting a strong third ordernonlinear response and efficient third harmonic generation in the optical regime. A thin germaniumnanodisk shows a pronounced valley in its scattering cross section close to the dark anapole mode,while the electric field energy inside the disk is maximized due to high confinement within thedielectric. We investigate the dependence of the third harmonic signal on disk size and pumpwavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a higheffective third order susceptibility of (3) = 4.3 10−9 , corresponding to an associated thirdharmonic conversion efficiency of 0.0001% at a wavelength of 1650 nm, which is four orders ofmagnitude greater than the case of an unstructured germanium reference film. Furthermore, thenonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonancesby about one order of magnitude, which is consistent with our numerical simulations. Thesefindings open new possibilities for the optimization of upconversion processes on the nanoscalethrough the appropriate engineering of suitable dielectric materials.
Grinblat G, Li Y, Nielsen MP, et al., 2016, Enhanced Third Harmonic Generation in Single Germanium Nanodisks Excited at the Anapole Mode, Nano Letters, Vol: 16, Pages: 4635-4640, ISSN: 1530-6992
We present an all-dielectric germanium nanosystem exhibiting a strong third order nonlinear response and efficient third harmonic generation in the optical regime. A thin germanium nanodisk shows a pronounced valley in its scattering cross section at the dark anapole mode, while the electric field energy inside the disk is maximized due to high confinement within the dielectric. We investigate the dependence of the third harmonic signal on disk size and pump wavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a high effective third order susceptibility of χ(3) = 4.3 × 10–9 esu, corresponding to an associated third harmonic conversion efficiency of 0.0001% at an excitation wavelength of 1650 nm, which is 4 orders of magnitude greater than the case of an unstructured germanium reference film. Furthermore, the nonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonances by about 1 order of magnitude, which is consistent with our numerical simulations. These findings open new possibilities for the optimization of upconversion processes on the nanoscale through the appropriate engineering of suitable dielectric materials.
Zhao W, Wang S, Liu B, et al., 2016, Exciton-plasmon coupling and electromagnetically induced transparency in monolayer semiconductors hybridized with Ag nanoparticles, Advanced Materials, Vol: 28, Pages: 2709-2715, ISSN: 1521-4095
Exciton–plasmon coupling in hybrids of a monolayer transition metal dichalcogenide and Ag nanoparticles is investigated in the weak and strong coupling regimes. In the weak coupling regime, both absorption enhancement and the Purcell effect collectively modify the photoluminescence properties of the semiconductor. In the strong coupling regime, electromagnetically induced transparency dips are displayed, evidencing coherent energy exchange between excitons and plasmons.
Gennaro SD, Roschuk TR, Maier SA, et al., 2016, Measuring chromatic aberrations in imaging systems using plasmonic nanoparticles, Optics Letters, Vol: 41, Pages: 1688-1691, ISSN: 1539-4794
We demonstrate a method to measure chromatic aberrations of microscope objectives with metallic nanoparticles using white light. Extinction spectra are recorded while scanning a single nanoparticle through a lens’s focal plane. We show a direct correlation between the focal wavelength and the longitudinal chromatic focal shift through our analysis of the variations between the scanned extinction spectra at each scan position and the peak extinction over the entire scan. The method has been tested on achromat and apochromat objectives using aluminum disks varying in size from 260–520 nm. Our method is straightforward, robust, low cost, and broadband with a sensitivity suitable for assessing longitudinal chromatic aberrations in high-numerical-aperture apochromatic corrected lenses.
Roeder R, Sidiropoulos TPH, Buschlinger R, et al., 2016, Mode Switching and Filtering in Nanowire Lasers, Nano Letters, Vol: 16, Pages: 2878-2884, ISSN: 1530-6992
Coherent light sources confining the light below the vacuum wavelength barrier will drive future concepts of nanosensing, nanospectroscopy, and photonic circuits. Here, we directly image the angular emission of such a light source based on single semiconductor nanowire lasers. It is confirmed that the lasing switches from the fundamental mode in a thin ZnO nanowire to an admixture of several transverse modes in thicker nanowires approximately at the multimode cutoff. The mode competition with higher order modes substantially slows down the laser dynamics. We show that efficient photonic mode filtering in tapered nanowires selects the desired fundamental mode for lasing with improved performance including power, efficiency, and directionality important for an optimal coupling between adjacent nanophotonic waveguides.
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