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The anatomy of plasmons

Description: From abstract: "Plamons (plasma-magnetic entities) are toroidal "packages" of plasma wrapped up in their own magnetic field. Experimental evidence for the existence of plasmons is adduced and theoretical considerations concerning their various types and their stability are discussed."
Date: November 15, 1955
Creator: Bostick, W. H.
Partner: UNT Libraries Government Documents Department

Terahertz spectroscopy of two-dimensional subwavelength plasmonic structures

Description: The fascinating properties of plasmonic structures have had significant impact on the development of next generation ultracompact photonic and optoelectronic components. We study two-dimensional plasmonic structures functioning at terahertz frequencies. Resonant terahertz response due to surface plasmons and dipole localized surface plasmons were investigated by the state-of-the-art terahertz time domain spectroscopy (THz-TDS) using both transmission and reflection configurations. Extraordinary terahertz transmission was demonstrated through the subwavelength metallic hole arrays made from good conducting metals as well as poor metals. Metallic arrays m!lde from Pb, generally a poor metal, and having optically thin thicknesses less than one-third of a skin depth also contributed in enhanced THz transmission. A direct transition of a surface plasmon resonance from a photonic crystal minimum was observed in a photo-doped semiconductor array. Electrical controls of the surface plasmon resonances by hybridization of the Schottkey diode between the metallic grating and the semiconductor substrate are investigated as a function of the applied reverse bias. In addition, we have demonstrated photo-induced creation and annihilation of surface plasmons with appropriate semiconductors at room temperature. According to the Fano model, the transmission properties are characterized by two essential contributions: resonant excitation of surface plasmons and nonresonant direct transmission. Such plasmonic structures may find fascinating applications in terahertz imaging, biomedical sensing, subwavelength terahertz spectroscopy, tunable filters, and integrated terahertz devices.
Date: January 1, 2009
Creator: Azad, Abul K; Chen, Houtong; Taylor, Antoinette; O' Hara, John F; Han, Jiaguang; Lu, Xinchao et al.
Partner: UNT Libraries Government Documents Department

Surface Plasmon Based Nanophotonic Optical Emitters

Description: Group- III nitride based semiconductors have emerged as the leading material for short wavelength optoelectronic devices. The InGaN alloy system forms a continuous and direct bandgap semiconductor spanning ultraviolet (UV) to blue/green wavelengths. An ideal and highly efficient light-emitting device can be designed by enhancing the spontaneous emission rate. This thesis deals with the design and fabrication of a visible light-emitting device using GaN/InGaN single quantum well (SQW) system with enhanced spontaneous emission. To increase the emission efficiency, layers of different metals, usually noble metals like silver, gold and aluminum are deposited on GaN/InGaN SQWs using metal evaporator. Surface characterization of metal-coated GaN/InGaN SQW samples was carried out using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Photoluminescence is used as a tool for optical characterization to study the enhancement in the light emitting structures. This thesis also compares characteristics of different metals on GaN/InGaN SQW system thus allowing selection of the most appropriate material for a particular application. It was found out that photons from the light emitter couple more to the surface plasmons if the bandgap of former is close to the surface plasmon resonant energy of particular metal. Absorption of light due to gold reduces the effective mean path of light emitted from the light emitter and hence quenches the quantum well emission peak compared to the uncoated sample.
Access: This item is restricted to the UNT Community Members at a UNT Libraries Location.
Date: December 2005
Creator: Vemuri, Padma Rekha
Partner: UNT Libraries

Terahertz detectors for long wavelength multi-spectral imaging.

Description: The purpose of this work was to develop a wavelength tunable detector for Terahertz spectroscopy and imaging. Our approach was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays. When this work began, grating-gate gate detectors, while having many promising characteristics, had a noise-equivalent power (NEP) of only 10{sup -5} W/{radical}Hz. Over the duration of this project, we have obtained a true NEP of 10{sup -8} W/{radical}Hz and a scaled NEP of 10{sup -9}W/{radical}Hz. The ultimate goal for these detectors is to reach a NEP in the 10{sup -9{yields}-10}W/{radical}Hz range; we have not yet seen a roadblock to continued improvement.
Date: October 1, 2007
Creator: Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur & Grine, Albert D.
Partner: UNT Libraries Government Documents Department

Nanoplasmonic molecular ruler for nuclease activity and DNAfootprinting

Description: We have constructed a nanoplasmonic molecular ruler, which can perform label-free and real-time monitoring of DNA length changes and perform DNA footprinting. The ruler was created by tethering double-stranded DNA to single Au nanoparticles. The scattering spectra of Au-DNA nanoconjugates showed red-shifted peak plasmon resonance wavelength dependent on DNA length, which can be measured with sub-nanometer axial resolution, averaging {approx}1.24 nm peak wavelength shift per DNA base pair. The spectra of individual Au-DNA nanoconjugates in the presence of nuclease showed a time-resolved dependence on the reaction dynamics, allowing quantitative, kinetic and real-time measurement of nuclease activity. The ruler was further developed into a new DNA footprinting platform. We showed the specific binding of a protein to DNA and the accurate mapping of its footprint. This work promises a very fast and convenient platform for mapping DNA-protein interactions, for nuclease activity monitoring, and for other DNA size-based methods.
Date: August 15, 2006
Creator: Chen, Fanqing Frank; Liu, Gang L.; Yin, Yadong; Gerion, Daniele; Kunchakarra, Siri; Mukherjee, Bipasha et al.
Partner: UNT Libraries Government Documents Department

Tunable plasmonic lattices of silver nanocrystals

Description: Silver nanocrystals are ideal building blocks for plasmonicmaterials that exhibit a wide range of unique and potentially usefuloptical phenomena. Individual nanocrystals display distinct opticalscattering spectra and can be assembled into hierarchical structures thatcouple strongly to external electromagnetic fields. This coupling, whichis mediated by surface plasmons, depends on their shape and arrangement.Here we demonstrate the bottom-up assembly of polyhedral silvernanocrystals into macroscopic two-dimensional superlattices using theLangmuir-Blodgett technique. Our ability to control interparticlespacing, density, and packing symmetry allows for tunability of theoptical response over the entire visible range. This assembly strategyoffers a new, practical approach to making novel plasmonic materials forapplication in spectroscopic sensors, sub-wavelength optics, andintegrated devices that utilize field enhancement effects.
Date: February 18, 2008
Creator: Tao, Andrea; Sinsermsuksakul, Prasert & Yang, Peidong
Partner: UNT Libraries Government Documents Department

Observations of Plasmons in Warm Dense Matter

Description: We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.
Date: September 5, 2006
Creator: Glenzer, S H; Landen, O L; Neumayer, P; Lee, R W; Widmann, K; Pollaine, S W et al.
Partner: UNT Libraries Government Documents Department

FUNCTIONALIZED LATERAL SURFACE COATED LASERS FOR CHEM-BIO DETECTION

Description: We present a class of compact, monolithic, photonic sensors consisting of multiple section edge emitting lasers with functionalized lateral surface coatings for low level detection of chemical or biological agents. Specifically, we discuss 8 {micro}m x 250 {micro}m Pd-coated H{sub 2} sensors and configurations to reduce the minimum detection limit from 138ppm for passive sensors to 1ppm for active sensors. Compared with conventional optical H{sub 2} sensors that use fiber gratings, surface plasmon resonances, or surface reflectance, our sensors offer the advantages of smaller size, wider dynamic range, monolithic integration of laser source and detector, and 2-D scalability to arrays of sensors that are functionalized to detect different agents.
Date: July 5, 2007
Creator: Goddard, L L; Bond, T C; Cole, G D & Behymer, E M
Partner: UNT Libraries Government Documents Department

Multiphonon Resonance Raman Scattering in InGaN

Description: In In{sub x}Ga{sub 1-x}N epitaxial films with 0.37 < x < 1 and free electron concentrations in the 10{sup 18} cm{sup -3} range, strong resonant Raman scattering of A{sub 1}(LO) phonon is observed for laser excitation in Raman scattering when excited above the direct band gaps. Examination of films with direct band gaps between 0.7 and 1.9 eV using laser energies from 1.9 to 2.7 eV shows that the resonance is broad, extending to up to 2 eV above the direct gap. Multiphonon Raman scattering with up to 5 LO phonons is also observed for excitation close to resonance in alloy samples; this is the highest number of phonon overtones ever observed for multiphonon scattering in a III-V compound under ambient conditions. Coupling of the electron plasmon to the LO phonon to form a longitudinal plasmon coupled mode of the type which is observed in the Raman spectra of n-GaN, appears not to occur in In{sub x}Ga{sub 1-x}N for x > 0.37.
Date: June 28, 2005
Creator: Ager, J. W., III; Walukiewicz, W.; Shan, W.; Yu, K. M.; Li, S. X.; Haller, E. E. et al.
Partner: UNT Libraries Government Documents Department

Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves

Description: With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the ...
Date: May 2012
Creator: Nagaraj, Nagaraj
Partner: UNT Libraries

Beat-wave generation of plasmons in semiconductor plasmas

Description: It is shown that in semiconductor plasmas, it is possible to generate large amplitude plasma waves by the beating of two laser beams with frequency difference close to the plasma frequency. For narrow gap seimconductors (for example n-type InSb), the system can simulate the physics underlying beat wave generation in relativistic gaseous plasmas.
Date: August 1, 1995
Creator: Berezhiani, V.I. & Mahajan, S.M.
Partner: UNT Libraries Government Documents Department

Giant, ultrafast optical switching based on an Insulator-to-MetalTransition in VO2 Nano-particles: Photo-activation of shape-controlledplasmons at 1.55 mu-m

Description: A new generation of devices where the electronic, optical or magnetic state of a system can be controlled optically on the ultrafast timescale is one of the most compelling technological ramifications of the rapidly advancing field of strongly correlated electrons. However, for real-world applications it is also necessary to incorporate these compounds in appropriate environments (e.g. optical fibers or silicon-based electronics), to ensure compatibility with existing technologies (e.g. telecom wavelengths), room temperature operation and limited power densities. Here, we report on the study of the photo-activated optical switching in nanorods of strongly correlated VO{sub 2}. The particles are grown by ion-implantation and self-assembly within a Silica matrix or an optical fiber, operate at room temperature and can be switched between the insulating and metallic phase within less than 100 fs. The energy threshold to achieve switching corresponds to approximately 500 pJ within the core of a single mode fiber and is compatible with current diode technologies. Tailoring of the spherical/cylindrical geometry results in control of the spectral response of the system, which is dominated by the impulsive formation of a surface plasmon upon the insulator-to-metal transition. The response at the technologically important 1.55 {micro}m wavelength is in this way maximized.
Date: July 1, 2004
Creator: Rini, M.; Cavalleri, A.; Schoenlein, R.W.; Lopez, R.; Feldman,C.; Haglund, R. et al.
Partner: UNT Libraries Government Documents Department

Using Plasmon Peaks in Electron Energy-Loss Spectroscopy to Determine the Physical and Mechanical Properties of Nanoscale Materials

Description: In this program, we developed new theoretical and experimental insights into understanding the relationships among fundamental universality and scaling phenomena, the solid-state physical and mechanical properties of materials, and the volume plasmon energy as measured by electron energy-loss spectroscopy (EELS). Particular achievements in these areas are summarized as follows: (i) Using a previously proposed physical model based on the universal binding-energy relation (UBER), we established close phenomenological connections regarding the influence of the valence electrons in materials on the longitudinal plasma oscillations (plasmons) and various solid-state properties such as the optical constants (including absorption and dispersion), elastic constants, cohesive energy, etc. (ii) We found that carbon materials, e.g., diamond, graphite, diamond-like carbons, hydrogenated and amorphous carbon films, exhibit strong correlations in density vs. Ep (or maximum of the volume plasmon peak) and density vs. hardness, both from available experimental data and ab initio DFT calculations. This allowed us to derive a three-dimensional relationship between hardness and the plasmon energy, that can be used to determine experimentally both hardness and density of carbon materials based on measurements of the plasmon peak position. (iii) As major experimental accomplishments, we demonstrated the possibility of in-situ monitoring of changes in the physical properties of materials with conditions, e.g., temperature, and we also applied a new plasmon ratio-imaging technique to map multiple physical properties of materials, such as the elastic moduli, cohesive energy and bonding electron density, with a sub-nanometer lateral resolution. This presents new capability for understanding material behavior. (iv) Lastly, we demonstrated a new physical phenomenon - electron-beam trapping, or “electron tweezers” - of a solid metal nanoparticle inside a liquid metal. This phenomenon is analogous to that of optical trapping of solid microparticles in solution known as "optical tweezers", which is currently being used to manipulate molecules and inorganic materials in a ...
Date: May 9, 2013
Creator: Howe, James M.
Partner: UNT Libraries Government Documents Department

Plasmons in strongly coupled shock-compressed matter

Description: We present the first measurements of the plasmon dispersion and damping in laser shock-compressed solid matter. Petawatt laser produced K-{alpha} radiation scatters on boron targets compressed by a 10 ns-long 400 J laser pulse. In the vicinity of the Fermi momentum, the scattering spectra show dispersionless, collisionally damped plasmons, indicating a strongly coupled electron liquid. These observations agree with x-ray scattering calculations that include both the Born-Mermin approximation to account for electron-ion collisional damping and local field corrections reflecting electron-electron correlations.
Date: April 15, 2010
Creator: Neumayer, P.; Fortmann, C.; Doppner, T.; Davis, P.; Falcone, R. W.; Kritcher, A. L. et al.
Partner: UNT Libraries Government Documents Department

Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals

Description: We present the first comprehensive investigation on water-soluble nanoparticles embedded into a paramagnetic shell and their properties as an MRI contrast agent. The nanoprobes are constructed with an inorganic core embedded into an ultra-thin silica shell covalently linked to chelated Gd{sup 3+} paramagnetic ions that act as an MRI contrast agent. The chelator contains the molecule DOTA and the inorganic core contains a fluorescent CdSe/ZnS qdots in Au nanoparticles. Optical properties of the cores (fluorescence emission or plasmon position) are not affected by the neither the silica shell nor the presence of the chelated paramagnetic ions. The resulting complex is a MRI/fluorescence probe with a diameter of 8 to 15 nm. This probe is highly soluble in high ionic strength buffers at pH ranging from {approx}4 to 11. In MRI experiments at clinical field strengths of 60 MHz, the QDs probes posses spin-lattice (T{sub 1}) and a spin-spin (T{sub 2}) relaxivities of 1018.6 +/- 19.4 mM{sup -1} s{sup -1} and 2438.1 +/- 46.3 mM{sup -1} s{sup -1} respectively for probes having {approx}8 nm. This increase in relaxivity has been correlated to the number of paramagnetic ions covalently linked to the silica shell, ranging from approximately 45 to over 320. We found that each bound chelated paramagnetic species contributes by over 23 mM{sup -1} s{sup -1} to the total T{sub 1} and by over 54 mM{sup -1} s{sup -1} to the total T{sub 2} relaxivity respectively. The contrast power is modulated by the number of paramagnetic moieties linked to the silica shell and is only limited by the number of chelated paramagnetic species that can be packed on the surface. So far, the sensitivity of our probes is in the 100 nM range for 8-10 nm particles and reaches 10 nM for particles with approximately 15-18 nm in diameter. The sensitivities ...
Date: August 28, 2006
Creator: Gerion, D; Herberg, J; Gjersing, E; Ramon, E; Maxwell, R; Gray, J W et al.
Partner: UNT Libraries Government Documents Department

Raman Spectroscopy Determination of Hole Concentration in p-Type GaSb

Description: Room temperature p-type GaSb bulk coupled mode spectra were measured as a function of hole concentration. These spectra were obtained using an optical system based on 752.55 nm excitation in order to obtain more sensitivity to bulk GaSb coupled mode scattering than possible with visible wavelength excitation-based systems. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated for determination of hole concentration from the bulk coupled mode spectra. Optically-derived values for hole concentration were determined by minimizing the sum of the residuals squared between an experimental and simulated spectrum as a function of total hole concentration and a plasmon damping parameter. Hole concentrations obtained from the Raman spectroscopic measurements deviated from the values determined from single field Hall effect measurements that were corrected to account for two band conduction by {approx}20% to {approx}65%. These deviations were attributed to the limitations of the spectral model employed and uncertainties in GaSb materials properties.
Date: April 5, 2007
Creator: Maslar JE, Hurst WS, Wang CA
Partner: UNT Libraries Government Documents Department

Terahertz-based target typing.

Description: The purpose of this work was to create a THz component set and understanding to aid in the rapid analysis of transient events. This includes the development of fast, tunable, THz detectors, along with filter components for use with standard detectors and accompanying models to simulate detonation signatures. The signature effort was crucial in order to know the spectral range to target for detection. Our approach for frequency agile detection was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays.
Date: September 1, 2008
Creator: Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur; Grine, Albert D. & Barrick, Todd A.
Partner: UNT Libraries Government Documents Department

Modification of Thermal Emission via Metallic Photonic Crystals

Description: Photonic crystals are materials that are periodically structured on an optical length scale. It was previously demonstrated that the glow, or thermal emission, of tungsten photonic crystals that have a specific structure - known as the 'woodpile structure' - could be modified to reduce the amount of infrared radiation from the material. This ability has implications for improving the efficiency of thermal emission sources and for thermophotovoltaic devices. The study of this effect had been limited because the fabrication of metallic woodpile structures had previously required a complex fabrication process. In this project we pursued several approaches to simplify the fabrication of metallic photonic crystals that are useful for modification of thermal emission. First, we used the self-assembly of micrometer-scale spheres into colloidal crystals known as synthetic opals. These opals can then be infiltrated with a metal and the spheres removed to obtain a structure, known as an inverse opal, in which a three-dimensional array of bubbles is embedded in a film. Second, we used direct laser writing, in which the focus of an infrared laser is moved through a thin film of photoresist to form lines by multiphoton polymerization. Proper layering of such lines can lead to a scaffold with the woodpile structure, which can be coated with a refractory metal. Third, we explored a completely new approach to modified thermal emission - thin metal foils that contain a simple periodic surface pattern, as shown in Fig. 1. When such a foil is heated, surface plasmons are excited that propagate along the metal interface. If these waves strike the pattern, they can be converted into thermal emission with specific properties.
Date: July 30, 2012
Creator: Norris, David J.; Stein, Andreas & George, Steven M.
Partner: UNT Libraries Government Documents Department

Solid-Density Plasma characterization with X-ray scattering on the 200-J Janus Laser

Description: We present collective x-ray scattering (CXS) measurements using a Chlorine He-{alpha} x-ray source pumped with less than 200 J of laser energy. The experimental scattering spectra show plasmon resonances from shocked samples. These experiments use only 10{sup 12} x-ray photons at the sample of which 10{sup -5} have been scattered and detected with a highly efficient curved crystal spectrometer. Our results demonstrate that x-ray scattering is a viable technique on smaller laser facilities making CXS measurements accessible to a broad scientific community.
Date: April 25, 2006
Creator: Neumayer, P B; Gregori, G; Ravasio, A; Price, D; Bastea, M; Landen, O L et al.
Partner: UNT Libraries Government Documents Department