187 research outputs found
On long-range plasmonic modes in metallic gaps
No full textSatuby and Orenstein [Opt. Express 15, 4247-4252 (2007)] reported the discovery and numerical and experimental investigation of long-range surface plasmon-polariton eigenmodes guided by wide (6 to 12 micrometer) rectangular gaps in 400 nm thick gold films using excitation of vacuum wavelength lambda = 1.55 micrometer. In this paper, we carry out a detailed numerical analysis of the two different types of plasmonic modes in these structures. We show that no long-range eigenmodes exists for these gap plasmon waveguides, and that the reported "modes" are likely to be beams of bulk waves and surface plasmons, rather than guided modes of the considered structures
On the Sherlocks, Jane Coleman and County Kildare in the Eighteen Forties
No full textIn the late 1980s and early 1990s the author acquired about 30,000 letters written mainly in the 1840s. These pertained to estates throughout Ireland managed by the firm of James Robert Stewart and Joseph Kincaid, hereafter denoted SK. Until the letters – called the SK correspondence in what follows – became the author’s property, they had not seen light of day since the 1840s. Addressed mainly to the firm’s office in Dublin, they were written by landlords, tenants, the partners in SK, local agents, etc. After about 200 years in operation as a land agency, the firm in which members of the Stewart family were the principal partners – Messrs J. R. Stewart & Son(s) from the mid- 1880s onwards – ceased operations in the mid-1980s. Since 1994 the author has been researching the SK correspondence of the 1840s. It gives many new insights into economic and social conditions in Ireland during the decade of the great famine, and into the operation of Ireland’s most important land agency during those years. It is intended ultimately to publish details on several of the estates managed by SK in a study more comprehensive than the present article, in book form. The proposed title is Landlords, tenants, famine: business of an Irish land agency in the 1840s, a draft of which has now been completed. A majority of the letters in that study are on themes some of which one might expect - rents, distraint (seizure of assets in lieu of rent); ‘voluntary’ surrender of land in return for ‘compensation’ upon quitting quietly; formal ejectment (a matter of last resort on estates managed by SK); landlordassisted emigration (on a scale much more extensive than most historians of Ireland in the 1840s appear to believe); petitions from tenants; complaints by tenants, both about other tenants and about local agents; landlord-financed and other relief of distress both before and during the great famine; major works of improvement (on almost all of the estates managed by SK which have been investigated in detail in the draft book); applications by SK, on behalf of landlords, for government loans to finance improvements; recommendations of agricultural advisers hired by SK, etc. Thus, most of the SK correspondence is about aspects of estate management. But the firm of SK was not only a manager of land. The correspondence reveals only two estates in Kildare, each of them relatively small, managed by SK in the 1840s. These were the lands of the Sherlocks near Naas and of Jane Coleman in the Kilcullen district. The correspondence on these properties differs substantively from most of those discussed in detail in the draft of Landlords, tenants, famine: first, it is relatively small in quantity, and secondly, it contains relatively little on the core aspects of estate management indicated above. Much of that on the Sherlocks focuses on misfortunes among family members, while the correspondence on Jane Coleman highlights the benevolence of that proprietor.
Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation
No full textHigh-refractive index nanostructured dielectrics have the ability to locally enhance electromagnetic fields with low losses while presenting high third-order nonlinearities. In this work, we exploit these characteristics to achieve efficient ultrafast all-optical modulation in a crystalline gallium phosphide (GaP) nanoantenna through the optical Kerr effect (OKE) and two-photon absorption (TPA) in the visible/near-infrared range. We show that an individual GaP nanodisk can yield differential reflectivity modulations of up to -40%, with characteristic modulation times between 14 and 66 fs, when probed at the anapole excitation (AE). Numerical simulations reveal that the AE represents a unique condition where both the OKE and TPA contribute with the same modulation sign, maximizing the response. These findings highly outperform previous reports on sub-100-fs all-optical switching from resonant nanoscale dielectrics, which have demonstrated modulation depths no larger than 0.5%, placing GaP nanoantennas as a promising choice for ultrafast all-optical modulation at the nanometer scale.Fil: Grinblat, Gustavo Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Zhang, Haizhong. Institute of Materials Research and Engineering; SingapurFil: Nielsen, Michael P.. University of New South Wales; AustraliaFil: Krivitsky, Leonid. Institute of Materials Research and Engineering; SingapurFil: Berté, Rodrigo. Ludwig Maximilians Universitat; AlemaniaFil: Li, Yi. Ludwig Maximilians Universitat; AlemaniaFil: Tilmann, Benjamin. Ludwig Maximilians Universitat; AlemaniaFil: Cortés, Emiliano. Ludwig Maximilians Universitat; AlemaniaFil: Oulton, Rupert F.. Imperial College London; Reino UnidoFil: Kuznetsov, Arseniy I.. Institute of Materials Research and Engineering; SingapurFil: Maier, Stefan A.. Ludwig Maximilians Universitat; Alemani
Semiconductor nanoplasmonics
No full textThe weak optical nonlinearities of natural materials restrict device sizes in photonic integrated circuits to dimensions far larger than conventional electronics. By exploiting the strong coupling between photons and collective electron oscillations in metals, plasmonics can confine light far below the Abbe diffraction limit. This increased confinement leads to enhanced nonlinear interactions that can be used for a wide range of applications. This thesis examines the integration of plasmonic components into semiconductor photonic architectures in order to utilize the strong light-matter interactions inherent in plasmonics to improve the performance of photonic integrated circuits.
In order to study integrated plasmonic devices, free-space laser light must first be coupled into the optical devices. To this end, a directional plasmonic-photonic coupler was designed to efficiently couple ultrashort pulses on-chip. Then, silicon hybrid gap plasmon waveguides (HGPWs) were studied for their waveguiding properties which includes the transition from photonic-like to plasmonic-like properties depending on gap width. Three-photon absorption photoluminescence in selectively deposited quantum dots showed the viability of these waveguides for extreme nanofocusing, which can be used to enhance light-matter interactions.
With the capability for high light intensities comes the possibility of nonlinear applications such as frequency mixing in the HGPWs. Four-wave mixing (FWM) in these waveguides was thus first explored theoretically and found to be promising, with conversion efficiencies comparable to photonic devices, and with no reliance upon phase-matching or dispersion considerations. The Z-scan measurement technique was utilized to explore organic polymers for the high nonlinearity and low refractive index necessary for plasmonics. Solution processing of such films is also advantageous for integrating the nonlinear material within nanoscopic gaps. Finally, once a suitable nonlinear polymer was found, FWM in the HGPWs was explored experimentally. These findings give further evidence of the capabilities of plasmonics to enable strong light-matter interactions in extremely small volumes.Open Acces
Giant and Tunable Optical Nonlinearity in Single‐Crystalline 2D Perovskites due to Excitonic and Plasma Effects
No full textMaterials with large optical nonlinearity, especially in the visible spectral region, are in great demand for applications in all-optical information processing and quantum optics. 2D hybrid Ruddlesden−Popper-type halide perovskites (RPPs) with tunable ultraviolet-to-visible direct bandgaps exhibit large nonlinear optical responses due to the strong excitonic effects present in their multiple quantum wells. Using a microscopic Z-scan setup with femtosecond laser pulses tunable across the visible spectrum, it is demonstrated that single-crystalline lead halide RPP nanosheets possess unprecedentedly large nonlinear refraction and absorption coefficients near excitonic resonances. A room-temperature insulator (exciton)–metal (plasma) Mott transition is found to occur near the exciton resonance of the thinnest qunatum-well RPPs, boosting the nonlinear response. Owing to the rapidly changing refractive index near resonance, a single RPP crystal can exhibit different nonlinear functionalities across the excitation spectrum. The results suggest that RPPs are efficient nonlinear materials in the visible waveband, indicating their potential use in integrated nonlinear photonic applications such as optical modulation and switching.Fil: Abdelwahab, Ibrahim. Imperial College London; Reino Unido. National University Of Singapore; SingapurFil: Dichtl, Paul. Imperial College London; Reino UnidoFil: Grinblat, Gustavo Sergio. Imperial College London; Reino UnidoFil: Leng, Kai. National University Of Singapore; SingapurFil: Chi, Xiao. National University Of Singapore; SingapurFil: Park, In-Hyeok. National University Of Singapore; SingapurFil: Nielsen, Michael P.. Imperial College London; Reino UnidoFil: Oulton, Rupert F.. Imperial College London; Reino UnidoFil: Loh, Kian Ping. National University Of Singapore; SingapurFil: Maier, Stefan A.. Imperial College London; Reino Unid
Scattering of Surface Plasmon Polaritons at Abrupt Surface\ud Discontinuities: Implications for Nano-Scale Cavities
No full textWe have developed a rigorous mode matching approach for the exact semi-analytical analysis\ud
of surface plasmon propagation across non-uniform semi-infinite dielectric-metal interfaces. We address two key deficiencies of related approaches in the literature: firstly, we resolve issues of accuracy and convergence and secondly, while we focus on the analysis of two-dimensional problems, we present a framework for three-dimensional problems for the first time. Analytical derivations of coupling coefficients between guided and radiation modes allow an efficient scattering matrix formulation to describe general structures with multiple discontinuities. Studies of the reflection, transmission and radiation of surface plasmons incident on both dielectric and metallic surface discontinuities show a correspondence with an effective Fresnel description. We also model a surface plasmon Distributed Bragg Reflector (DBR) capable of reflecting between 80% and 90% of incident surface plasmon power. Radiation mode scattering ultimately limits the DBR’s reflection performance rather than the intrinsic absorption of the metal. Thus alternative plasmonic geometries that suppress radiation modes, such as gap and channel structures, could be superior for the design of strongly reflective DBRs for integration in high Q-factor nano-scale cavities. We anticipate that this method will be an invaluable tool for the efficient and intuitive design of plasmonic devices based on structural non-uniformities
Confinement and propagation characteristics of subwavelength plasmonic modes
No full textWe have studied subwavelength confinement of the surface plasmon polariton modes of various plasmonic waveguides and examined their relative merits using a graphical parametric representation of their confinement and propagation characteristics. While the same plasmonic phenomenon governs mode confinement in all these waveguides, the various architectures can exhibit distinctive behavior in terms of effective mode area and propagation distance. We found that the waveguides based on metal and one dielectric material show a similar trade-off between energy confinement and propagation distance. However, a hybrid plasmon waveguide, incorporating metal, low index and high index dielectric materials, exhibits longer propagation distances for the same degree of confinement. We also point out that plasmonic waveguides with sharp features can provide an extremely strong local field enhancement, which is not necessarily accompanied by strong confinement of the total electromagnetic energy. In these waveguides, a mode may couple strongly to nearby atoms, but suffer relatively low propagation losses due to weak confinement
Organic-inorganic perovskite plasmonic nanowire lasers with a low threshold and a good thermal stability
No full textUltrafast All-Optical Modulation in 2D Hybrid Perovskites
No full textTwo-dimensional (2D) hybrid organic-inorganic Ruddlesden-Popper perovskites (RPPs) have been recently shown to exhibit large nonlinear optical properties due to the strong excitonic effects present in their multiple quantum wells. In this work, we use nondegenerate pump-probe spectroscopy in the 600-1000 nm wavelength range to study the influence of nonlinear effects on the ultrafast dynamics of 2D RPP thin flakes. We find that, under sub-bandgap excitation, â100 nm thick perovskite sheets allow up to â2% reflectivity modulation within a 20 fs period, due to the nonlinear optical Kerr effect and two-photon absorption, surpassing by a factor of â5 the reported nonlinear performance of photonic metasurfaces and single nanoantennas. When the excitation is resonant with the excitonic absorption, the ultrafast nature of the nonlinear response is lost due to the presence of linear absorption creating long-lived free carriers. Our results suggest that 2D RPPs are potential nanoscale all-optical modulators in the visible/near-infrared waveband for applications such as ultrafast information processing, optical data transmission, and high-performance computing.Fil: Grinblat, Gustavo Sergio. Imperial College London; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Abdelwahab, Ibrahim. Imperial College London; Reino Unido. National University of Singapore; SingapurFil: Nielsen, Michael P.. Imperial College London; Reino Unido. University of New South Wales; AustraliaFil: Dichtl, Paul. Imperial College London; Reino UnidoFil: Leng, Kai. National University of Singapore; SingapurFil: Oulton, Rupert F.. Imperial College London; Reino UnidoFil: Loh, Kian Ping. National University of Singapore; SingapurFil: Maier, Stefan A.. Imperial College London; Reino Unido. Ludwig Maximilians Universitat; Alemani
Hot carrier optoelectronic phenomena in van der Waals heterostructures
No full textTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) exhibit fascinating optical properties including strong light-matter coupling, prominent excitonic effects, and valley-selective circular dichroism. These properties render TMDs as a potential component for advanced optoelectronics devices. One of the most remarkable phenomena of 2D TMDs is the ultrafast charge transfer of photocarriers across van der Waals (vdW) interfaces, which potentially allows realization of hot carrier optoelectronic devices. Hot photocarrier and exciton dynamics in 2D TMDs depend on intrinsic and extrinsic factors such as many-body effects and interface electronic states. Thus, the prospects for exploiting the photophysical properties of 2D TMDs and their heterostructures for hot carrier optoelectronic devices remain largely unexplored. In this thesis, experimental studies on the photophysics and optoelectronic device properties of 2D TMD-based vdW heterostructures are presented. The first part of this thesis discusses an unconventional electro-optic light upconverter. It is shown that ultrafast interlayer transfer of photoexcited carriers can be electrically induced, allowing upconversion of relatively weak continuous wave laser light. The second part reports on efficient exciton-exciton annihilation (EEA) process in monolayer TMDs. We discover that encapsulation of TMD within hexagonal boron nitride (hBN) films strongly suppresses EEA. The last part reports on unusually robust photocurrent response in a metal-insulator-semiconductor (MIS) heterostructure. It is shown that generation of high energy free carriers via efficient EEA plays a fundamental role in the observed unusual photoresponse of the heterostructures.Open Acces
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