Journal ArticlePhysical Review Letters · January 17, 2025
Coupling is an essential mechanism that drives complexity in natural systems, transforming single, noninteracting elements into intricate networks with rich physical properties. Here, we demonstrate a chip-scale coupled laser system that exhibits complex o ...
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Journal ArticleOptics Express · December 2, 2024
This erratum corrects a misstatement regarding the absence of non-integrable singularities in 2d distributed Raman sensing applications and a formula [Eq. (9)] for one case of Raman enhancement. These changes do not impact the other results present ...
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Journal ArticleCommunications Engineering · December 1, 2024
It is not currently possible for an infrared camera to see through a hot window. The window’s own blinding thermal emission prevents objects on the other side from being imaged. Here, we demonstrate a path to overcoming this challenge by coating a hot wind ...
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Journal ArticleNano letters · June 2024
Aluminum nanocrystals created by catalyst-driven colloidal synthesis support excellent plasmonic properties, due to their high level of elemental purity, monocrystallinity, and controlled size and shape. Reduction in the rate of nanocrystal growth enables ...
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Journal ArticleAdvanced Optical Materials · April 4, 2024
Hybrid light–matter coupled states, or polaritons, in magnetic materials have attracted significant attention due to their potential for enabling novel applications in spintronics and quantum information processing. However, most magnon-polariton studies i ...
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Journal ArticleProceedings of the National Academy of Sciences of the United States of America · March 2024
Aluminum nanocrystals (AlNCs) are of increasing interest as sustainable, earth-abundant nanoparticles for visible wavelength plasmonics and as versatile nanoantennas for energy-efficient plasmonic photocatalysis. Here, we show that annealing AlNCs under va ...
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ConferenceCLEO: Science and Innovations, CLEO: S and I 2024 in Proceedings CLEO 2024, Part of Conference on Lasers and Electro-Optics · January 1, 2024
We present an improved numerical model for quantum cascade laser pumped molecular lasers (QPMLs) and present predictions of QPML performance for various molecular gases such as OCS, NH3, N2O, CH3F, HCN or H2O. ...
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Conference2024 Conference on Lasers and Electro-Optics, CLEO 2024 · January 1, 2024
We present an improved numerical model for quantum cascade laser pumped molecular lasers (QPMLs) and present predictions of QPML performance for various molecular gases such as OCS, NH3, N2O, CH3F, HCN or H2O. ...
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Conference2024 Conference on Lasers and Electro-Optics, CLEO 2024 · January 1, 2024
We present an improved numerical model for quantum cascade laser pumped molecular lasers (QPMLs) and present predictions of QPML performance for various molecular gases such as OCS, NH3, N2O, CH3F, HCN or H2O. ...
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Journal ArticleNanoscale · June 2023
For the conversion of CO2 into fuels and chemical feedstocks, hybrid gas/liquid-fed electrochemical flow reactors provide advantages in selectivity and production rates over traditional liquid phase reactors. However, fundamental questions remai ...
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Journal ArticleOptical Materials Express · June 1, 2023
Ring laser gyroscopes (RLGs) based on non-Hermitian exceptional points (EPs) have garnered much recent interest due to their exceptional sensitivity. Such gyroscopes typically consist of two-ring laser resonators, one with loss and one with an equal amount ...
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Journal ArticleOptical Materials Express · June 1, 2023
This is an introduction to the feature issue of Optical Materials Express on Non-Hermitian Optics and Photonics. ...
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Journal ArticleNano letters · April 2023
The performance of photocatalysts and photovoltaic devices can be enhanced by energetic charge carriers produced from plasmon decay, and the lifetime of these energetic carriers greatly affects overall efficiencies. Although hot electron lifetimes in plasm ...
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Journal ArticleOptics express · January 2023
We present a general framework for inverse design of nanopatterned surfaces that maximize spatially averaged surface-enhanced Raman (SERS) spectra from molecules distributed randomly throughout a material or fluid, building upon a recently proposed trace f ...
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Conference2023 Conference on Lasers and Electro-Optics, CLEO 2023 · January 1, 2023
Non-Hermitian optics provides a unique platform to take advantage of absorption losses in materials and control radiative properties. We demonstrate a non-Hermitian metasurface that exhibit directional suppression of thermal radiation while maintaining tra ...
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ConferenceCLEO: Fundamental Science, CLEO:FS 2023 · January 1, 2023
Non-Hermitian optics provides a unique platform to take advantage of absorption losses in materials and control radiative properties. We demonstrate a non-Hermitian metasurface that exhibit directional suppression of thermal radiation while maintaining tra ...
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Journal ArticleApplied spectroscopy · December 2022
Although gas phase rotational spectroscopy is a mature field for which millions of rotational spectral lines have been measured in hundreds of molecules with sub-MHz accuracy, it remains a challenge to measure these rotational spectra in excited vibrationa ...
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Journal ArticleACS Energy Letters · October 14, 2022
Plasmonic metal nanostructures have garnered rapidly increasing interest as heterogeneous photocatalysts, facilitating chemical bond activation and overcoming the high energy demands of conventional thermal catalysis. Here we report the highly efficient pl ...
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Journal ArticleNano letters · September 2022
Plasmonic nanostructures have attracted increasing interest in the fields of photochemistry and photocatalysis for their ability to enhance reactivity and tune reaction selectivity, a benefit of their strong interactions with light and their multiple energ ...
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Journal ArticleACS Applied Energy Materials · August 22, 2022
Hybrid gas/liquid-fed electrochemical flow reactors may become attractive alternatives for chemical synthesis once it is understood how catalytic product selectivity may be optimized through the control of gas phase reactants. Using a constant pH basic ele ...
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Journal ArticleACS nano · April 2022
Plasmon-induced photocatalysis is a topic of rapidly increasing interest, due to its potential for substantially lowering reaction barriers and temperatures and for increasing the selectivity of chemical reactions. Of particular interest for plasmonic phot ...
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Journal ArticleApplied Physics Letters · February 21, 2022
Gaseous ammonia has previously been demonstrated as a compelling gain medium for a quantum cascade laser pumped molecular laser (QPML) exhibiting good power efficiency. Here, we explore the potential of the ammonia QPML to produce powerful, broadly tunable ...
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Journal ArticleNanophotonics · February 2, 2022
The synergy between topology and non-Hermiticity in photonics holds immense potential for next-generation optical devices that are robust against defects. However, most demonstrations of non-Hermitian and topological photonics have been limited to super-wa ...
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Journal ArticleAPL Photonics · January 1, 2022
Despite decades of research, no frequency tunable sources span the terahertz gap between 0.3 and 3 THz. By introducing methyl fluoride (CH3F) as a new gain medium for a quantum cascade laser-pumped molecular laser (QPML), we demonstrate continuous-wave las ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2022
The synergy between topology and non-Hermiticity in photonics holds potential for optical devices that are robust against defects. We demonstrate a non-Hermitian plasmonic-dielectric metasurface in the visible with non-trivial topology. ...
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Conference2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings · January 1, 2022
The synergy between topology and non-Hermiticity in photonics holds potential for optical devices that are robust against defects. We demonstrate a non-Hermitian plasmonic-dielectric metasurface in the visible with non-trivial topology. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2022
The quantum cascade laser pump molecular laser (QPML) is a tunable source of terahertz frequencies operating at room temperature that can easily scale beyond the milliwatt level. We present here new progress in QPML research. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2022
Infrared/Terahertz double resonance spectroscopy is explored for remote identification of trace molecular gases at atmospheric pressures. Free induction decay of low pressure hyperfine-resolved transitions in CH335Cl inform a roadmap for future atmospheric ...
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Journal ArticleAPL Photonics · November 1, 2021
The ability to image strain fields in composite materials is an indispensable necessity for structural health monitoring. Embedded electromagnetic metamaterials sensitive to applied stresses and operating in the terahertz regime have been proposed as a sol ...
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Journal ArticlePhysical Review Applied · August 1, 2021
Quantum-cascade-laser-(QCL) pumped molecular lasers (QPMLs) have recently been introduced as a source of powerful (>1 mW) tunable (>1 THz) narrow-band (<10 kHz) continuous-wave terahertz radiation. The performance of these lasers depends critically on mole ...
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Conference2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings · May 1, 2021
We demonstrate a quantum cascade laser-pumped terahertz laser using methyl fluoride gas. The large dipole moment of this molecule allows for a low threshold laser with frequency tunable emission spanning more than one terahertz. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2021
We demonstrate a quantum cascade laser-pumped terahertz laser using methyl fluoride gas. The large dipole moment of this molecule allows for a low threshold laser with frequency tunable emission spanning more than one terahertz. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2021
Terahertz metamaterials that exhibit broad spectral resonances are used to probe local strain fields. By choosing specific frequencies and polarizations for measurement, it is possible to obtain unique spatial maps for different strain states. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2021
In preparation for remote atmospheric detection, preliminary double resonance spectroscopic measurements were made of CH3Cl and CH3F using a LWIR pump to excite transient vibrational states and a THz source to probe the rotational levels. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2021
We demonstrate and characterize a new quantum cascade laser-pumped molecular laser using methyl fluoride as its gain medium. We show that a laser using this gain medium can exhibit a low pump threshold while allowing emission over more than 100 lines spann ...
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Chapter · January 1, 2021
This chapter introduces a methodology to distinguish the thermal and nonthermal contributions in an illuminated, plasmon-enhanced catalyst. Although nonthermal effects in light-driven reactions are deservedly drawing much attention, photothermal effects ma ...
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ConferenceInternational Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz · November 8, 2020
Terahertz metamaterials with strain-sensitive junctions are introduced to identify structurally compromised regions of composite materials. Spatially mapping the local polarimetric metamaterial response visualizes and records regions of stress extrema expe ...
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ConferenceOptics InfoBase Conference Papers · September 14, 2020
Charge separation in ZnO/ZnS type II heterostructures may prove useful as a photocatalyst support. This work used cathodoluminescence spectroscopy to explore whether thermal annealing of ZnO and ZnS powders can synthesize such heterostructures. ...
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Journal ArticleNano Research · May 1, 2020
Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel fo ...
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ConferenceConference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS · May 1, 2020
We demonstrate a new type of Terahertz Gas Laser pumped by a tunable solid-state laser. This laser has a wide tuning range and operates at room temperature with a high efficiency in a very compact design. ...
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Journal ArticleJournal of Physical Chemistry C · April 2, 2020
Localized surface plasmon resonances optically excited in metallic nanoparticles (NPs) produce beneficial thermal and nonthermal effects. Nonthermal effects, such as enhancing and localizing fields on subwavelength scales and photo-generating hot carriers, ...
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Journal ArticleAdvances in Optics and Photonics · March 31, 2020
This tutorial describes the application of digital holography to the terahertz spectral region and demonstrates how to reconstruct images of complex dielectric targets. Using highly coherent terahertz sources, high-fidelity amplitude and phase reconstructi ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · January 1, 2020
An overview on our latest research on UV plasmonics with Rh and Ga metal nanostructures is presented. We will pay attention to their plasmonic performance and UV tunability. For Ga, its polymorphism will be analyzed and for Rh three characteristic geometri ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2020
We demonstrate a new type of Terahertz Gas Laser pumped by a tunable solid-state laser. This laser has a wide tuning range and operates at room temperature with a high efficiency in a very compact design. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2020
Terahertz metamaterials with strain-sensitive junctions are introduced to identify structurally compromised regions of composite materials. Spatially mapping the local polarimetric metamaterial response visualizes and records regions of stress extrema expe ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2020
Double resonant spectroscopy measurements are presented using a tunable 9-11 μm pump source with a sub-nanosecond pulse train output. This method is demonstrated at atmospheric pressure for methyl halides using a THz probe. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2020
We demonstrate a new class of optically pumped far-infrared lasers using quantum cascade lasers as the pump. Following an initial demonstration using nitrous oxide, we show how we can generate light at THz frequencies using different gases. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2020
This work presents the design and performance of a 10 μm sub-picosecond laser source. Initial measurements of high-intensity atmospheric propagation are also presented, which represent the first kilometer-range studies of ultrashort pulses in this waveleng ...
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Journal ArticleGranular Matter · November 1, 2019
A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a century, whether in the service of art, education, or sci ...
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Journal ArticleScience (New York, N.Y.) · November 2019
The terahertz region of the electromagnetic spectrum has been the least utilized owing to inadequacies of available sources. We introduce a compact, widely frequency-tunable, extremely bright source of terahertz radiation: a gas-phase molecular laser based ...
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Journal ArticleNano Research · August 1, 2019
In some cases, illumination of traditional thermal catalysts and tailored plasmonic photocatalysts may synergistically combine thermal and nonthermal mechanisms to enhance reaction rates and improve product selectivity at reduced temperatures. To understan ...
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Journal ArticleAdvanced Optical Materials · July 4, 2019
Interest in gallium (Ga) is growing rapidly, thanks in part to its wide spectral tunability and its intriguing temperature-dependent polymorphism. In order to exploit and control phase-change plasmonics in the liquid and solid phases of Ga, an accurate und ...
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Journal ArticleMaterials Today · July 1, 2019
Many epoxy adhesives require high temperatures to bond composite materials. However, oven heating severely restricts what may be attached or enclosed within composite material-based structures and greatly limits the possibilities for repair. Inspired by in ...
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Journal ArticleJournal of Luminescence · July 1, 2019
The effect of Al doping on the nature of ultraviolet (UV) near band edge emission and broadband “green” visible emission from deep defects in ZnO nanowires is explored by temperature- and excitation intensity-dependent photoluminescence (PL) spectroscopy. ...
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Journal ArticleACS Energy Letters · May 31, 2019
Synthetic ammonia has been the primary worldwide source of agricultural fertilizer over the last century and is a promising carbon-free energy carrier for sustainable transportation. Despite its global importance, synthetic ammonia produced with the Haber- ...
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Journal ArticleAdvanced Optical Materials · May 3, 2019
Mapping strain fields in visually opaque structural composites—for which failure is often sudden, irreparable, and even catastrophic—requires techniques to locate and record regions of stress, fatigue, and incipient failure. Many composite materials are tr ...
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Journal ArticleThe Review of scientific instruments · May 2019
Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial recons ...
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Journal ArticleNano letters · March 2019
Industrial scale catalytic chemical synthesis demands both high reaction rates and high product yields. In exothermic chemical reactions, these conflicting objectives require a complex balance of optimized catalysts, high temperatures, high pressures, and ...
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Journal ArticleScientific reports · February 2019
The reflected microwave power from the photo-excited high mobility GaAs/AlGaAs 2D device has been measured over the wide frequency band spanning from 30 to 330 GHz simultaneously along with diagonal magnetoresistance as a function of the magnetic field. Ea ...
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Journal ArticleOptical Materials Express · January 1, 2019
In order to exploit gallium's (Ga) rich polymorphism in the design of phase-change plasmonic systems, accurate understanding of the dielectric function of the different Ga-phases is crucial. The dielectric dispersion profiles of those phases appearing at a ...
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ConferenceInternational Conference on Metamaterials, Photonic Crystals and Plasmonics · January 1, 2019
Epoxy materials are widely used for efficient bonding and repair of composite materials. Plasmonic nanoparticles can be employed as heat source to improve curing of epoxy films. We theoretically show how the nanoparticle-assisted photothermal curing is a f ...
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Journal ArticleACS Photonics · August 15, 2018
Rotational spectroscopy is introduced as a new in situ method for monitoring gas-phase reactants and products during chemical reactions. Exploiting its unambiguous molecular recognition specificity and extraordinary detection sensitivity, rotational spectr ...
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Journal ArticleProceedings of the National Academy of Sciences of the United States of America · June 2018
We present both an innovative theoretical model and an experimental validation of a molecular gas optically pumped far-infrared (OPFIR) laser at 0.25 THz that exhibits 10× greater efficiency (39% of the Manley-Rowe limit) and 1,000× smaller volume than com ...
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Journal ArticleNano letters · March 2018
In plasmon-enhanced heterogeneous catalysis, illumination accelerates reaction rates by generating hot carriers and hot surfaces in the constituent nanostructured metals. In order to understand how photogenerated carriers enhance the nonthermal reaction ra ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2018
We present experimental studies of the linear and nonlinear optical response of switchable terahertz metasurfaces, using terahertz ellipsometry and nonlinear transmission spectroscopy with intense THz pulses. ...
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Journal ArticleNanomaterials (Basel, Switzerland) · December 2017
For applications of surface-enhanced spectroscopy and photocatalysis, the ultraviolet (UV) plasmonic behavior and charge distribution within rhodium nanocubes is explored by a detailed numerical analysis. The strongest plasmonic hot-spots and charge concen ...
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Journal ArticleApplied Physics Letters · November 6, 2017
Switchable metasurfaces fabricated on a doped epi-layer have become an important platform for developing techniques to control terahertz (THz) radiation, as a DC bias can modulate the transmission characteristics of the metasurface. To model and understand ...
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Journal ArticleIEEE Transactions on Terahertz Science and Technology · November 1, 2017
A rail-mounted synthetic aperture radar has been constructed to operate at W-band (75-110 GHz) and a terahertz (THz) band (325-500 GHz) in order to ascertain its ability to detect and locate isolated small, visually obscured metallic scatterers embedded in ...
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Conference2017 Conference on Lasers and Electro-Optics, CLEO 2017 - Proceedings · October 25, 2017
We perform experimental characterization of switchable THz metasurfaces using variable-angle broadband THz ellipsometry. We extract frequency dependent surface susceptibility tensors and model the applied DC bias as tuning the conductivity of the active la ...
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ConferenceInternational Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz · October 12, 2017
We describe experimental measurements and simulations of a switchable THz metasurface device in a slab waveguide geometry. The device exhibits giant phase modulation of the TE1 mode at particular frequencies determined by the metamaterial geometry. Simulat ...
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Journal ArticleJournal of Infrared, Millimeter, and Terahertz Waves · September 1, 2017
Flexible metamaterial films, fabricated by photolithography on a thin copper-backed polyimide substrate, are used to mark or barcode objects securely. The films are characterized by continuous-wave terahertz spectroscopic ellipsometry and visualized by a s ...
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ConferenceJournal of Physics: Conference Series · August 15, 2017
Remotely sensed microwave reflection was measured concurrently with standard magnetotransport in photo-excited high mobility GaAs/AlGaAs heterostructure. Experiments indicate strong reflection resonance on both sides of the magnetic field axis for linearly ...
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Journal ArticleJournal of the Optical Society of America. A, Optics, image science, and vision · July 2017
The combination of wide bandwidth W-band inverse synthetic aperture radar imagery and high-fidelity numerical simulations has been used to identify distinguishing signatures from simple metallic and dielectric targets. Targets are located with millimeter-s ...
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Journal ArticlePhysical Review B · May 3, 2017
Millimeter wave radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D electron system under bichromatic excitation in order to study the evolution of the oscillatory diagonal magnetoresistance, Rxx as the millimeter wave inten ...
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Journal ArticleAIP Advances · March 1, 2017
A high Al-content (y > 0.4) multi-quantum-well (MQW) structure with a quaternary InxAlyGa(1-x-y)N active layer was synthesized using plasma-assisted molecular beam epitaxy. The MQW structure exhibits strong carrier confinement and room temperature ultravio ...
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Journal ArticleOptics express · February 2017
In order to improve speed and efficiency over traditional scanning methods, a Bayesian compressive sensing algorithm using adaptive spatial sampling is developed for single detector millimeter wave synthetic aperture imaging. The application of this algori ...
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Journal ArticleChemical Engineering World · February 1, 2017
Duke University researchers have developed tiny nanoparticies that help convert carbon dioxide into methane using only ultraviolet light as an energy source. In the past two decades, scientists have explored new and useful ways that light can be used to ad ...
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Journal ArticleJournal of Materials Chemistry C · January 1, 2017
The mechanism for producing efficient white light phosphors from sulfidated zinc oxide (ZnO) powders is elucidated. ZnO powders prepared by vacuum annealing produce powders of oxygen-deficient ZnO:Zn, while ZnO powders annealed in a sulfur atmosphere produ ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · January 1, 2017
Plasmonics in the UV-range constitutes a new focus of research due to new challenges arising in fields such as biology, chemistry or spectroscopy. Very recent studies point out gallium and rhodium as good candidates for these purposes because of their low ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2017
We perform experimental characterization of switchable THz metasurfaces using variable-angle broadband THz ellipsometry. We extract frequency dependent surface susceptibility tensors and model the applied DC bias as tuning the conductivity of the active la ...
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Chapter · January 1, 2017
This chapter focuses on ultrafast nonlinear spectroscopy at the ultraviolet M- or saddle-point in the electronic bandstructure of graphene where the position and dynamical evolution of its absorption peak are especially sensitive to electron-phonon interac ...
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Conference2016 Conference on Lasers and Electro-Optics, CLEO 2016 · December 16, 2016
Electron-phonon coupling in graphene is studied across the Brillouin zone. The contributions from modulated hopping and conventional deformation potential coupling, and from intraband and interband coupling are analyzed and related to available experimenta ...
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ConferenceInternational Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz · November 28, 2016
We describe experimental characterization of switchable THz metasurfaces using variable-angle broadband THz ellipsometry. A theoretical framework is used to extract surface susceptibility tensors as a function of frequency and applied DC bias. This will al ...
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Journal ArticleOptics express · September 2016
The ultraviolet (UV) range presents new challenges for plasmonics, with interesting applications ranging from engineering to biology. In previous research, gallium, aluminum, and magnesium were found to be very promising UV plasmonic metals. However, a nat ...
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ConferenceOptics InfoBase Conference Papers · July 18, 2016
An Off-axis Fresnel interferometric imager was constructed to acquire holograms using a highly coherent, narrowband, continuous wave source tunable over 0.3-1.0 THz. Fresnel and angular spectrum reconstruction methods of amplitude and phase holograms are p ...
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Journal ArticleLangmuir : the ACS journal of surfaces and colloids · May 2016
Organic-inorganic hybrid materials formed by sequential vapor infiltration (SVI) of trimethylaluminum into polyester fibers are demonstrated, and the photoluminescence of the fibers is evaluated using a combined UV-vis and photoluminescence excitation (PLE ...
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Journal ArticleApplied Physics Letters · April 4, 2016
Conventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a sim ...
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Journal ArticleACS nano · April 2016
The intense local field induced near metallic nanostructures provides strong enhancements for surface-enhanced spectroscopies, a major focus of plasmonics research over the past decade. Here we consider that plasmonic nanoparticles can also induce remarkab ...
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Journal ArticleJournal of Physical Chemistry C · March 17, 2016
Simultaneous transmission infrared (IR) absorption and photoluminescence (PL) spectroscopies are used to reveal the correlation of free electron and defect densities during the stepwise annealing of ZnO nanocrystals in high vacuum. For increasing annealing ...
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Journal ArticlePhysical Review B · February 8, 2016
Recently, optical probes have become available that can access and observe energy renormalization due to electron-phonon interaction in graphene away from the well-studied Dirac K point. Using an expanded deformation potential approach, we present a theore ...
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Journal ArticleNano letters · February 2016
Hydrogen dissociation is a critical step in many hydrogenation reactions central to industrial chemical production and pollutant removal. This step typically utilizes the favorable band structure of precious metal catalysts like platinum and palladium to a ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · January 1, 2016
Plasmonics in the UV-range constitutes a new challenge due to the increasing demand to detect, identify and destroy biological toxins, enhance biological imaging, and characterize semiconductor devices at the nanometer scale. Silver and aluminum have an ef ...
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Journal ArticleNanoscale horizons · January 2016
Polydisperse rhodium nanoparticles have recently shown promise for ultraviolet (UV) plasmonics, but controlling the size and morphology of metal nanoparticles is essential for tuning surface plasmon resonances. Here we report the use of slow-injection poly ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2016
Electron-phonon coupling in graphene is studied across the Brillouin zone. The contributions from modulated hopping and conventional deformation potential coupling, and from intraband and interband coupling are analyzed and related to available experimenta ...
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Journal ArticleACS nano · November 2015
Aluminum is an abundant and high-quality material for plasmonics with potential for large-area, low-cost photonic technologies. Here we examine aluminum nanoclusters with plasmonic Fano resonances that can be tuned from the near-UV into the visible region ...
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Journal ArticleApplied Physics Letters · September 28, 2015
Thin films of the wide bandgap quaternary semiconductor InxAlyGa(1-x-y)N with low In (x=0.01-0.05) and high Al composition (y=0.40-0.49) were synthesized on GaN templates by plasma-assisted molecular beam epitaxy. High-reso ...
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Journal ArticleJournal of Physical Chemistry C · June 4, 2015
Local field enhancements produced by metal nanoparticles have been widely investigated in the visible range for common metals like gold and silver, but recent interest in ultraviolet plasmonics has required consideration of alternate metals. Aluminum and g ...
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Journal ArticleNano letters · April 2015
We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icos ...
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Journal ArticleNano letters · February 2015
The nonoxidizing catalytic noble metal rhodium is introduced for ultraviolet plasmonics. Planar tripods of 8 nm Rh nanoparticles, synthesized by a modified polyol reduction method, have a calculated local surface plasmon resonance near 330 nm. By attaching ...
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Journal ArticleACS nano · February 2015
Gallium has recently been demonstrated as a phase-change plasmonic material offering UV tunability, facile synthesis, and a remarkable stability due to its thin, self-terminating native oxide. However, the dense irregular nanoparticle (NP) ensembles fabric ...
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Journal ArticleIEEE Transactions on Terahertz Science and Technology · January 1, 2015
Terahertz digital off-axis holography (THzDH) has been demonstrated as a non-destructive tool for imaging voids within visually opaque dielectrics. Using a raster scanning heterodyne detector, the imager captures lensless transmission holograms formed by t ...
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Chapter · January 1, 2015
This chapter considers the challenge of using terahertz (THz) techniques for the detection and recognition of explosives. There are two general approaches to this problem: (1) imaging, which uses the penetration capability of THz radiation to “see” the ima ...
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Journal ArticlePhysical Review Applied · November 26, 2014
The practicality of a newly proposed infrared-terahertz (IR-THz) double-resonance (DR) spectroscopic technique for remote trace-gas identification is explored. The strength of the DR signatures depends on known molecular parameters from which a combination ...
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ConferenceInternational Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz · November 13, 2014
Terahertz digital off-axis holography has been demonstrated as a non-destructive imaging tool for three-dimensional (3D) printed structures. Digital holographic reconstructions from two structures were used to measure the imager's modulation transfer funct ...
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ConferenceInternational Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz · November 13, 2014
Spatially different arrangements of identical metaatoms in a unit cell bring about distinct properties in stereometamaterials. Integrating the stereometamaterial into a perfect metamaterial absorber, we designed, fabricated, and characterized a device with ...
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Journal ArticleJournal of Materials Research · November 12, 2014
Fibrous polyethylene terephthalate (PET) was modified by organometallic vapor exposure to form hybrid materials with unique photoluminescent characteristics. Using a sequential vapor infiltration (SVI) process, the elongated exposures of trimethylaluminum ...
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ConferenceOptics InfoBase Conference Papers · October 14, 2014
We studied the electron-phonon and electron-electron interactions in graphene and its heterostructures using pump-probe spectroscopy. Graphene on hexa-Boron Nitride undergoes band structure modification, which affects the relaxation mechanisms of the hot c ...
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ConferenceOptics InfoBase Conference Papers · October 14, 2014
High frequency differential transmission spectroscopy of graphene, probing near the Mpoint, is performed and analyzed theoretically. Electron-phonon coupling is identified as the chief mechanism for renormalization with an effective acoustic deformation po ...
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Journal ArticleApplied Physics Letters · September 29, 2014
InAlN films deposited by plasma-assisted molecular beam epitaxy exhibited a lateral composition modulation characterized by 10-12 nm diameter, honeycomb-shaped, columnar domains with Al-rich cores and In-rich boundaries. To ascertain the effect of this mic ...
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ConferenceProceedings - 2014 Summer Topicals Meeting Series, SUM 2014 · September 18, 2014
Zinc oxide (ZnO) is a major wide band gap semiconductor material for optoelectronic and photonic devices because of its exceptional optical properties, arising from the combination of a wide band gap (~3.37 eV) and a large exciton binding energy ...
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Journal ArticleACS Photonics · July 16, 2014
Self-assembled, irregular ensembles of hemispherical Ga nanoparticles (NPs) were deposited on sapphire by molecular beam epitaxy. These samples, whose constituent unimodal or bimodal distribution of NP sizes was controlled by deposition time, exhibited loc ...
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Journal ArticleOptics express · June 2014
We apply adaptive sensing techniques to the problem of locating sparse metallic scatterers using high-resolution, frequency modulated continuous wave W-band RADAR. Using a single detector, a frequency stepped source, and a lateral translation stage, invers ...
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Journal ArticlePhysical review letters · May 2014
The role of many-body interactions is experimentally and theoretically investigated near the saddle point absorption peak of graphene. The time and energy-resolved differential optical transmission measurements reveal the dominant role played by electron-a ...
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Journal ArticleJournal of Luminescence · January 1, 2014
The effect of Al doping concentration and oxygen ambient pressure on the structural and optical properties of chemical vapor deposition-grown, Al-doped ZnO nanowires is studied. As Al doping increases, the strength of the broad visible emission band decrea ...
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Journal ArticleACS nano · January 2014
Unlike silver and gold, aluminum has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the ultraviolet. This extended response, combined with its natural abundance, low cost, and amenabil ...
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ConferenceFiber Society 2014 Fall Meeting and Technical Conference: Fibers for ÃÂïÃÂÿÃÂý the Future · January 1, 2014
Depth profiling of poly(ethylene terephthalate) (PET) fibers modified with trimethylaluminum (TMA) using transmission electron microscopy (TEM), atomic force microscopy (AFM), and atomic force microscope-based infrared spectroscopy (AFM-IR). ...
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ConferenceFiber Society 2014 Fall Meeting and Technical Conference: Fibers for the Future · January 1, 2014
Depth profiling of poly(ethylene terephthalate) (PET) fibers modified with trimethylaluminum (TMA) using transmission electron microscopy (TEM), atomic force microscopy (AFM), and atomic force microscope-based infrared spectroscopy (AFM-IR). ...
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ConferenceConference on Lasers and Electro-Optics Europe - Technical Digest · January 1, 2014
High frequency differential transmission spectroscopy of graphene, probing near the Mpoint, is performed and analyzed theoretically. Electron-phonon coupling is identified as the chief mechanism for renormalization with an effective acoustic deformation po ...
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ConferenceLaser Science, LS 2014 · January 1, 2014
High frequency differential transmission spectroscopy of graphene, probing near the Mpoint, is performed and analyzed theoretically. Electron-phonon coupling is identified as the chief mechanism for renormalization with an effective acoustic deformation po ...
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ConferenceLaser Science, LS 2014 · January 1, 2014
We studied the electron-phonon and electron-electron interactions in graphene and its heterostructures using pump-probe spectroscopy. Graphene on hexa-Boron Nitride undergoes band structure modification, which affects the relaxation mechanisms of the hot c ...
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Journal ArticleTurkish Journal of Physics · January 1, 2014
What has turned into highly complex and somewhat misunderstood efficiency loss mechanisms occurring in light-emitting diodes (LEDs) based on the InN-GaN material system at high injection levels are discussed. Suggestions are made as to the dominant mechani ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2014
High frequency differential transmission spectroscopy of graphene, probing near the Mpoint, is performed and analyzed theoretically. Electron-phonon coupling is identified as the chief mechanism for renormalization with an effective acoustic deformation po ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2014
High frequency differential transmission spectroscopy of graphene, probing near the Mpoint, is performed and analyzed theoretically. Electron-phonon coupling is identified as the chief mechanism for renormalization with an effective acoustic deformation po ...
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Journal ArticleApplied Physics Letters · November 11, 2013
The quantum efficiencies of both the band edge and deep-level defect emission from annealed ZnO powders were measured as a function of excitation fluence and wavelength from a tunable sub-picosecond source. A simple model of excitonic decay reproduces the ...
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Journal ArticleApplied Physics Letters · October 28, 2013
Low defect density asymmetric multiple quantum wells (MQWs) of InGaN/GaN grown on non-polar a-plane GaN substrates were investigated using time-integrated and time-resolved photoluminescence spectroscopy. Comparison of these spectra with the predicted emis ...
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Journal ArticleJournal of Physical Chemistry C · September 26, 2013
The practical efficacy of technologically promising metals for use in ultraviolet plasmonics (3-6 eV) is assessed by an exhaustive numerical analysis. This begins with estimates of the near- and far-field electromagnetic enhancement factors of isolated hem ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · June 17, 2013
We examine and compare the diagonal magnetoresistance, Rxx, and the photovoltage induced by microwave (42≤f<300 GHz) and terahertz (f≥300 GHz) photoexcitation in the high mobility quasi-two-dimensional GaAs/AlGaAs system. The data demonstrate strong radiat ...
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Journal ArticleNano letters · June 2013
Self-assembled arrays of hemispherical gallium nanoparticles deposited by molecular beam epitaxy on a sapphire support are explored as a new type of substrate for ultraviolet plasmonics. Spin-casting a 5 nm film of crystal violet upon these nanoparticles p ...
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Journal ArticleApplied Physics Letters · April 15, 2013
We show that N-doped ZnO films grown on sapphire can exhibit significant (∼1018 cm-3) room-temperature p-type behavior when sufficient nitrogen (N) is incorporated and the material is annealed appropriately. Substitutional N on the oxygen (O) sublattice is ...
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Journal ArticleJournal of Applied Physics · April 7, 2013
A series of continuous-wave spectroscopic measurements elucidates the mechanism responsible for the technologically important green emission from deep-level traps in ZnO:Zn powders. Analysis of low-temperature photoluminescence (PL) and PL excitation spect ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · December 1, 2012
In recent years a great amount of research has been focused on metamaterials, initially for fabrication of left-handed materials for use in devices such as superlenses or electromagnetic cloaking. Such devices have been developed and demonstrated in regime ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · December 1, 2012
Imaging with electromagnetic radiation in the THz frequency regime, between 0.2 THz and 10 THz, has made considerable progress in recent years due to the unique properties of THz radiation, such as being non-ionizing and transparent through many materials. ...
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ConferenceOptics InfoBase Conference Papers · December 1, 2012
This talk will survey the application of digital holographic and tomographic techniques to highly coherent, single frequency terahertz sources and extremely sensitive heterodyne receivers for high resolution three dimensional reconstructions of extended, v ...
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ConferenceFrontiers in Optics, FIO 2012 · December 1, 2012
We report on a Terahertz imaging methodology that combines digital holography and polarimetry to characterize objects in transmission and reflection geometries on their geometrical and physical properties in the Terahertz region between 0.3 - 1.0 THz. Digi ...
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Journal ArticleNano letters · November 2012
The use of aluminum for plasmonic nanostructures opens up new possibilities, such as access to short-wavelength regions of the spectrum, complementary metal-oxide-semiconductor (CMOS) compatibility, and the possibility of low-cost, sustainable, mass-produc ...
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Journal ArticlePhysical Review A - Atomic, Molecular, and Optical Physics · May 16, 2012
A method for highly selective remote sensing of atmospheric trace polar molecular gases is described. Based on infrared-terahertz double-resonance spectroscopic techniques, the molecule-specific coincidence between the lines of a CO 2 laser and rotational- ...
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Journal ArticleOptics letters · April 2012
Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interfe ...
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Journal ArticleOptics express · January 2012
Surface-enhanced Raman Scattering (SERS) is studied in sub-wavelength metallic gratings on a substrate using a rigorous electromagnetic approach. In the ultraviolet SERS is limited by the metallic dampening, yet enhancements as large as 10(5) are predicted ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2012
This talk will survey the application of digital holographic and tomographic techniques to highly coherent, single frequency terahertz sources and extremely sensitive heterodyne receivers for high resolution three dimensional reconstructions of extended, v ...
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Journal ArticleNano Research · 2012
We present a bottom-up synthesis, spectroscopic characterization, and ab initio simulations of star-shaped hexagonal zinc oxide (ZnO) nanowires. The ZnO nanostructures were synthesized by a low-temperature hydrothermal growth method. The cross-section of t ...
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ConferenceIRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves · December 1, 2011
IR/THz double resonance spectroscopy has recently been proposed as a method of chemical remote sensing with isotopic molecular recognition specificity at atmospheric pressures for distances approaching one kilometer. Double resonance signatures are calcula ...
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ConferenceIRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves · December 1, 2011
Terahertz digital off-axis holography is demonstrated with a highly coherent, frequency tunable continuous wave terahertz source emitting between 0.1 and 0.8 THz and a single spatially-scanned Schottky diode detector. The angular spectrum and dual waveleng ...
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ConferenceIRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves · December 1, 2011
We report high throughput, continuous wave terahertz imaging using a near-field funnel aperture with adjustable output diameter. The frequency dependence of the output power and resolution immediately following the aperture are reported, as are the propaga ...
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ConferenceIRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves · December 1, 2011
A reconfigurable, all-reflective terahertz imager has been constructed, capable of 4096-pixel resolution in 20 seconds. The imager spans 0.09-0.90 THz in 5 bands, each represented by a 16-element detector array. Both, beam profiling and confocal imaging co ...
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Journal ArticleNano letters · September 2011
Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depen ...
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Journal ArticleProceedings of SPIE - The International Society for Optical Engineering · May 23, 2011
Researchers at the Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) have initiated multidiscipline efforts to develop nano-based structures and components for insertion into advanced missile, aviation, and autonomous air and ...
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Journal ArticleOptics express · May 2011
Terahertz digital off-axis holography is demonstrated using a Mach-Zehnder interferometer with a highly coherent, frequency tunable, continuous wave terahertz source emitting around 0.7 THz and a single, spatially-scanned Schottky diode detector. The recon ...
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Journal ArticleOptics express · April 2011
We investigate laser emission from optically-pumped rotationally excited molecular gases confined in a metallic cavity. To this end, we have developed a theoretical framework able to accurately describe, both in the spatial and temporal domains, the molecu ...
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ConferenceApplied Mechanics and Materials · December 1, 2010
Total hip replacement is a highly successful operation; restoring function and reducing pain in arthritis patients. In recent years, thinner resurfacing acetabular cups have been introduced in order to preserve bone stock and reduce the risk of dislocation ...
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Journal ArticleOptics letters · November 2010
A transmissive, square-wave Ronchi phase grating has been fabricated from the dielectric polytetrafluoroethylene to diffract an ~0.7 THz beam quasi-optically. When illuminated by a coherent, cw terahertz (THz) source, the spot separation of the ±1 diffract ...
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Journal ArticlePhysica Status Solidi (A) Applications and Materials Science · August 1, 2010
Europium-doped gadolinium oxide (Gd2O3) thin films were deposited on sapphire substrates by pulsed laser deposition (PLD). The effect of oxygen pressure during deposition on the structure of the thin films, investigated by transmission electron microscopy ...
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Journal ArticlePhysica Status Solidi (B) Basic Research · July 1, 2010
In pulsed laser deposition of the sesquioxide semiconductor Gd2O3, adjusting the chamber oxygen pressure controls the crystalline structure of the host. This technique was used to deposit thin films of nominally 1.6% by weight europiumdoped, cubic phase Gd ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · June 22, 2010
The standalone, portable Terahertz (THz) Imaging Profiler Array (TIPA) based on an Offner Relay design has been constructed as a THz beam profiler and multispectral imager. It integrates a solid-state detector technology (Schottky Diodes) that can be confi ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · June 22, 2010
Single resonance chemical remote sensing, such as Fourier-transform infrared spectroscopy, has limited recognition specificity because of atmospheric pressure broadening. Active interrogation techniques promise much greater chemical recognition that can ov ...
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Journal ArticleJournal of Applied Physics · May 15, 2010
Europium gallium oxide (Eux Ga1-x) 2 O3 thin films were deposited on sapphire substrates by pulsed laser deposition with varying Eu content from x=2.4 to 20 mol %. The optical and physical effects of high europium concentration on these thin films were stu ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · March 15, 2010
Ultrafast time-resolved photoluminescence spectroscopy following one- and two-photon excitations of ZnO powder is used to gain unprecedented insight into the surprisingly high external quantum efficiency of its "green" defect emission band. The role of exc ...
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Journal ArticleIEEE Journal of Quantum Electronics · December 1, 2009
The remote sensing of gases in complex mixtures at atmospheric pressure is a challenging problem and much attention has been paid to it. The most fundamental difference between this application and highly successful astrophysical and upper atmospheric remo ...
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Journal ArticleJournal of Vacuum Science and Technology B · October 2009
The effects of various deposition techniques on the photoluminescence spectra of the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-(1-cyanovinylene) phenylene] (MEH-CN-PPV) are investigated. Photoluminescence spectroscopy provides insight to t ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · September 8, 2009
Laser induced Semiconductor Switches (LSS), comprised of a gap antenna deposited on a semiconductor substrate and photoexcited by a pulsed laser, are the primary source of THz radiation utilized in time-domain spectroscopy (TDS). THz-TDS applications such ...
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Journal ArticleJournal of the American Chemical Society · September 2009
Size-controlled gallium nanoparticles deposited on sapphire were explored as alternative substrates to enhance Raman spectral signatures. Gallium's resilience following oxidation is inherently advantageous in comparison with silver for practical ex vacuo n ...
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Journal ArticleEPL · August 1, 2009
We report on photoluminescence (PL) measurements at 85 K for GaN/Al 0.2Ga0.8N surface quantum wells (SQWs) with a width in the range of 1.51-2.9 nm. The PL spectra show a redshift with decreasing SQW width, in contrast to the blueshift normally observed fo ...
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Journal ArticleProceedings of SPIE - The International Society for Optical Engineering · June 15, 2009
Nonstoichiometric ZnO with an excess of Zn atoms (ZnO:Zn) has a long history of use as a green/monochrome phosphor in electron-excited vacuum fluorescent and field emission displays. The advent of ultraviolet lasers and light emitting diodes presents the p ...
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Journal ArticleJournal of Applied Physics · May 8, 2009
We provide experimental evidence for direct and indirect excitations of photoluminescence (PL) from Tm-doped AlxGa1-xN of varying Al content. Direct excitation of Tm3+ ions is observed primarily at 85 K through transitions 3H6 → 1I 6, 3P0, 3P1, and 3P2 whe ...
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Journal ArticleJournal of Physical Chemistry C · March 12, 2009
A facile, template-free method was used to grow large areas of well-aligned ZnO nanowire arrays on amorphous SiO 2 substrates. The arrays are composed of vertically aligned, single-crystalline, wurtzitic [001] ZnO nanowires whose diameters were easily cont ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · March 3, 2009
We provide evidence that the Tm3+ -induced defects in Tm-doped Alx Ga1-x N hosts play a major role in the nonradiative transfer of the excitation energy from the I1 6 state to the D1 2 state of Tm3+ ions from which the most efficient photoluminescence (PL) ...
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Journal ArticleJournal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures · February 17, 2009
Highly reactive N-polar [000-1] GaN surfaces were analyzed using spectroscopic ellipsometry. Following exposure to air, observed changes in the pseudodielectric function near the GaN band edge indicate that surface contamination reduces the band bending. A ...
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Journal ArticleLangmuir · January 2009
Ga nanoparticles supported on large band gap semiconductors like SiC, GaN, and ZnO are interesting for plasmon-enhanced UV-emitting solid-state devices. We investigate the influence of the polarity of the SiC, GaN, and ZnO wurtzite semiconductors on the we ...
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ConferenceMaterials Science and Engineering: B · May 15, 2008
Beta phase gallium oxide thin films deposited by pulsed laser deposition are efficient hosts for rare earth metals such as europium. In this study europium doped gallium oxide deposited on glass substrates is used to make red (611 nm) electroluminescent de ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · April 21, 2008
The effect of plasma-induced ion damage on the optical properties of ZnO films grown by plasma-assisted molecular beam epitaxy on a-sapphire substrates and GaN(0001)/c-sapphire templates prepared has been studied using steady-state and time-resolved photol ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · March 20, 2008
Indium kinetics and evidence for indium segregation on the GaN (0001) surface are investigated via in situ spectroscopic ellipsometry. Indium deposition exhibits two stable states at coverages of 1.0 and 1.7 ML within the temperature range of 630-688°C. Fo ...
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Journal ArticleOptics InfoBase Conference Papers · January 1, 2008
We demonstrate novel use of in situ spectroscopic ellipsometry to probe in real-time metal nanoparticle deposition. Real-time monitoring of NP assembly plasmon resonance enables control of NP size via the plasmon resonance and vice versa. ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2008
We demonstrate novel use of in situ spectroscopic ellipsometry to probe in real-time metal nanoparticle deposition. Real-time monitoring of NP assembly plasmon resonance enables control of NP size via the plasmon resonance and vice versa. ...
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Journal ArticleJournal of Applied Physics · October 22, 2007
Photoluminescence (PL), photoluminescence excitation (PLE), and time-resolved PL spectroscopies have been carried out at room temperature and 86 K on transitions from D25, D15, and D05 excited states to numerous FJ7 ground states of Eu-doped GaN films grow ...
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Journal ArticleJournal of Applied Physics · September 20, 2007
We report on epitaxial lateral overgrowth (ELO) of (11 2- 0) a -plane GaN by metalorganic chemical vapor deposition. Different growth rates of Ga- and N-polar wings together with wing tilt create a major obstacle for achieving a smooth, fully coalesced sur ...
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Journal ArticleJournal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures · June 11, 2007
Spectroscopic ellipsometry installed on a GEN-II plasma assisted molecular beam epitaxy machine has been shown to be an effective in situ real time tool for monitoring the kinetics of gallium adlayer adsorption/desorption on the GaN surface. In this work, ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · May 24, 2007
We report on growth and characterization of epitaxial lateral overgrown (ELO) (112̄0) a-plane GaN by metalorganic chemical vapor deposition (MOCVD). The ELO samples were grown using a SiO2 striped mask pattern consisting of 4 μm wide open windows and 10 μm ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · May 24, 2007
ZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies as well as X-ray diffraction and transmission electron microscopy showed that ZnO nanorods grew mostly perpe ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · May 24, 2007
GaN epitaxial layers grown on SiC and sapphire suffer from high density of line and point defects. To address this problem, new growth methods using in situ or ex situ nano-network masks as dislocation filters have been introduced recently. In this work, w ...
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Journal ArticleApplied Physics Letters · February 5, 2007
Significant improvement of structural and optical qualities of GaN thin films on sapphire substrates was achieved by metal organic chemical vapor deposition with in situ Si Nx nanonetwork. Transmission electron microscope (TEM) studies revealed that screw- ...
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Journal ArticleApplied Physics Letters · 2007
Liquid Ga nanoparticles have been deposited on sapphire substrates at room temperature. The optical evolution of Ga nanoparticle surface plasmon resonance during deposition has been characterized by in situ real-time spectroscopic ellipsometry to control a ...
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Journal ArticleJournal of Applied Physics · December 1, 2006
Epitaxial ZnO films codoped with tellurium and nitrogen were grown by pulsed laser deposition on c -axis oriented sapphire substrates. The codoping strategy allowed the resistivity of the films to be controlled over several orders of magnitude and may prov ...
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Journal ArticleApplied Physics Letters · December 1, 2006
Epitaxial lateral overgrowth (ELO) was employed for both c -plane and a -plane GaN layers on sapphire, and a more pronounced optical improvement was observed for the a -plane GaN as evidenced by the significantly increased band edge photoluminescence (PL). ...
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Journal ArticleApplied Physics Letters · November 13, 2006
In situ spectroscopic ellipsometry kinetic characterization is used to monitor the behavior of Ga atoms during and after Ga flux impingement upon a (0001) GaN surface at various temperatures in the range of 680-750 °C. The observed saturation of the pseudo ...
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Journal ArticleNano letters · June 2006
Sulfur-doped zinc oxide (ZnO) nanowires grown on gold-coated silicon substrates inside a horizontal tube furnace exhibit remarkably strong visible wavelength emission with a quantum efficiency of 30%, an integrated intensity 1600 times stronger than band e ...
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Journal ArticleApplied Physics Letters · May 29, 2006
Europium-doped Β- Ga2 O3 thin films were grown on double-side polished c -axis (0001) sapphire substrates by pulsed laser deposition at 850 °C. Transmission measurements of the films revealed a sharp band edge with a band gap at 5.0 eV. The films exhibited ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · May 24, 2006
We report on the structural, electrical, and optical characterization of GaN epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) on SiN x and TiN x, porous templates in order to reduce the density of extended defects. Observations by t ...
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ConferenceJournal of Electronic Materials · April 1, 2006
Thermal conductivities (K) of melt-grown bulk ZnO samples thermally treated under different conditions were measured using scanning thermal microscopy. Samples annealed in air at 1050°C for 3 h and treated with N-plasma at 750°C for 1 min. exhibited κ = 1. ...
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ConferenceMaterials Science Forum · January 1, 2006
Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on in situ-formed SiN and TiN porous network templates. The room temperature carrier decay time of 1.86 ns measured for a T ...
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ConferenceMaterials Research Society Symposium Proceedings · January 1, 2006
ZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies showed that ZnO nanorods grew mostly perpendicular to the GaN substrate surface, whereas a more random direc ...
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Book · December 1, 2005
Practical quantum computing still seems more than a decade away, and researchers have not even identified what the best physical implementation of a quantum bit will be. There is a real need in the scientific literature for a dialog on the topic of lessons ...
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ConferenceMaterials Research Society Symposium Proceedings · August 25, 2005
Recently, wide band gap II-IV-N 2 semiconductors such as ZnSiN 2, and ZnGeN 2 and ZnSiGeN 2 have been synthesized, but very little is known about their band structure, optical properties, or electronic properties. Bulk crystals are hard to synthesize becau ...
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Journal ArticleSuperlattices and Microstructures · August 1, 2005
Ultrafast optical probes, photoluminescence spectroscopy, and Raman spectroscopy have been applied to investigate carrier dynamics in nitride-based binary and ternary, and dilute nitride semiconductors. Carrier dynamics in the form of radiative and non-rad ...
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Journal ArticleApplied Physics Letters · June 6, 2005
Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on TiN porous network templates formed by in situ thermal annealing of Ti in ammonia. The room-temperature decay times obta ...
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Journal ArticleJournal of Applied Physics · May 15, 2005
Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on SiN and TiN porous network templates. The room-temperature decay times obtained from biexponential fits to time-resolved ...
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Journal ArticleApplied Physics Letters · March 21, 2005
II-IV- N2 wide band gap semiconductors such as ZnSi N2, ZnGe N2, and ZnSiGe N2 have potential uses for nonlinear materials and as lattice matching compounds for the growth of SiC and GaN devices. In this study, the dispersion of the TE and TM indices of re ...
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Journal ArticleIEEE Transactions on Nanotechnology · March 1, 2005
The dependence of radiative recombination rate and efficiency on GaN quantum-dot (QD) size and temperature is studied by time-resolved photoluminescence (PL) spectroscopy. The emission is dominated by radiative recombination at low temperatures (<125 K) an ...
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Journal ArticleApplied Physics Letters · January 31, 2005
Photoluminescence (PL) excitation spectroscopy mapped the photoexcitation wavelength dependence of the red luminescence (D05 → F27) from GaN:Eu. Time-resolved PL measurements revealed that for excitation at the GaN bound exciton energy, the decay transient ...
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Journal ArticleOptics InfoBase Conference Papers · January 1, 2005
Broadband, visible-wavelength emission of unprecedented brightness from ZnO nanowires is characterized by steady-state and ultrafast time-resolved spectroscopy. Energy transfer is explored by simultaneously studying the unusually fast decay of band edge em ...
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ConferenceMaterials Research Society Symposium Proceedings · January 1, 2005
The GaN:RE phosphor development plays a major role in the GaN:RE AC thick dielectric electroluminescent (TDEL) device optimization. In this paper we report on EL devices fabricated using Eu-doped GaN red phosphors films grown by interrupted growth epitaxy ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2005
Broadband, visible-wavelength emission of unprecedented brightness from ZnO nanowires is characterized by steady-state and ultrafast time-resolved spectroscopy. Energy transfer is explored by simultaneously studying the unusually fast decay of band edge em ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · November 1, 2004
The optical properties of a high quality bulk ZnO, thermally post treated in a forming gas environment are investigated by temperature dependent continuous wave and time-resolved photoluminescence (PL) measurements. Several bound and free exciton transitio ...
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ConferenceProceedings of SPIE - The International Society for Optical Engineering · August 16, 2004
In this study, stimulated emission (SE) and ultrafast carrier relaxation are explored in InGaN and AlGaN/GaN multiple quantum wells (MQWs). The SE threshold densities (I th) in InGaN MQWs increase with increasing QW depth. By contrast, no significant varia ...
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Journal ArticleJournal of Applied Physics · June 15, 2004
Time-resolved photoluminescence measurements of the 5D 0→ 7F 2 and 5G 0→ 7F 3 transitions were performed for investigating the temperature-dependent energy transfer mechanisms of Eu-doped GaN. Numerically integrated rate equation models enabled the analysi ...
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Journal ArticleApplied Physics Letters · April 26, 2004
A measurement of stimulated emission (SE) from ZnO thin films grown on c-plane sapphire by rf sputtering was performed. At 10 K, free exciton transitions were observed in the photoluminescence (PL), transmission and reflection spectra of the sample anneale ...
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ConferenceConference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series · December 1, 2003
Strain-induced modification of recombination dynamics in single layer (SQDs) and stacked (MQDs) GaN quantum dots is compared by time-resolved photoluminescence spectroscopy. Large strain induced built-in fields increases the radiative recombination time in ...
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Journal ArticleApplied Physics Letters · June 9, 2003
The stimulated emission and ultrafast carrier relaxation in AlGaN/GaN multiple quantum wells were analyzed. The room temperature, time-resolved, differential transmission measurements were used to map the carrier relaxation mechanism for above barrier ener ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · April 11, 2003
Room-temperature, wavelength-nondegenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well (QW) structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength a ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · April 1, 2003
Room-temperature, wavelength-nondegenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well (QW) structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength a ...
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Journal ArticleApplied Physics Letters · March 3, 2003
A study was performed on ultrafast carrier relaxation and simulated emission (SE) in InGaN multiple quantum wells (MQW). Two InGaN MQW laser structures with different QW In compositions x was used to measure SE. It was found that SE threshold energy densit ...
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Journal ArticleIEEE Transactions on Nanotechnology · March 1, 2003
Self-assembled GaN quantum dots (QDs), grown on AlN by molecular beam epitaxy, were investigated by time-resolved photoluminescence spectroscopy. We investigate the emission mechanism in GaN QDs by comparing the carrier recombination dynamics in single and ...
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ConferenceOSA Trends in Optics and Photonics Series · January 1, 2003
A spectroscopic study of Eu-doped GaN grown on silicon by solid state molecular beam epitaxy is presented. The temperature dependence of the continuous-wave and time-resolved luminescence properties reveals details about the energy transfer rates and therm ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2003
Strain-induced modification of recombination dynamics in single layer (SQDs) and stacked (MQDs) GaN quantum dots is compared by time-resolved photoluminescence spectroscopy. Large strain induced built-in fields increases the radiative recombination time in ...
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ConferenceOptics InfoBase Conference Papers · January 1, 2003
A spectroscopic study of Eu-doped GaN grown on silicon by solid state molecular beam epitaxy is presented. The temperature dependence of the continuous-wave and time-resolved luminescence properties reveals details about the energy transfer rates and therm ...
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Journal ArticlePhysical Review B - Condensed Matter and Materials Physics · October 15, 2002
Using time-resolved photoluminescence measurements, the recombination rate in an In0.18Ga0.82N/GaN quantum well (QW) is shown to be greatly enhanced when spontaneous emission is resonantly coupled to a silver surface plasmon. The rate of enhanced spontaneo ...
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Journal ArticleMonthly Notices of the Royal Astronomical Society · September 21, 2002
We present the results of a survey for variable stars in the core of the globular cluster M3. Our findings include the discovery of 11 new or suspected variables, including a possible W Vir, and the first period determinations for 13 previously known varia ...
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ConferenceConference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series · January 1, 2002
Coherent bulk and zone folded longitudinal acoustic phonons were generated in InGaN MQWs using impulsive optical techniques. It was observed that the frequency of the oscillations was changed by the changing quantum well period. The bulk phonon transport i ...
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ConferenceConference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series · January 1, 2002
Spontaneous emission rate in nitrides was enhanced. The degree of enhancement increased with increasing film thickness and decreasing GaN cap layer thickness. Enhancement factors of almost 100 were indicated by dramatically accelerated TRPL decay at a freq ...
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Journal ArticleApplied Physics Letters · December 17, 2001
Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic AlxGa1-xN epitaxial layers with 0.0≤x≤1.0 throughout the visible wavelength region. The dispersion, measured by a prism coupling waveguide te ...
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Journal ArticlePhysica Status Solidi (A) Applied Research · November 1, 2001
Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic AlxGa1-xN epitaxial layers with 0 ≤ x ≤ 1.0 throughout the visible wavelength region 457 nm < λ < 800 nm. The dispersion, measured by a prism ...
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Journal ArticlePhysical review letters · June 2001
Using subpicosecond optical pump-probe techniques, coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were investigated in an InGaN multiple quantum well structure. A two-pump differential transmission technique was used to generate and control co ...
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ConferencePhysica Status Solidi (B) Basic Research · January 1, 2001
Sub-picosecond optical pump-probe techniques were used to generate coherent zone-folded longitudinal acoustic phonons (ZFLAPs) in an InGaN multiple quantum well structure. Differential transmission measurements revealed that carriers injected near the barr ...
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Journal ArticleOptics and Photonics News · January 1, 2001
Control behavior of coherent acoustic phonons was studied. Acoustic phonons in semiconductor multiple quantum wells (MQW) are expected to have very long coherence times. Semiconductor MQWs produce zone folding of the acoustic phonon branch, allowing direct ...
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Journal ArticleApplied Physics Letters · July 3, 2000
Subpicosecond wavelength-degenerate differential transmission optical spectroscopy was used to characterize the electron capture time in a 10-period InxGa1-xN multiple-quantum-well (MQW) structure. Photoluminescence and photoluminescence excitation spectro ...
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Journal ArticleApplied Physics Letters · February 21, 2000
Indices of refraction for MgxZn1-xO epitaxial films grown by pulsed-laser deposition on sapphire substrates with x up to 0.36 were determined in the range of wavelength 457-968 nm by analysis of optical transmission spectra and prism-coupled waveguide meas ...
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Journal ArticleIEEE Transactions on Microwave Theory and Techniques · December 1, 1999
Square and triangular lattice two-dimensional (2-D) photonic crystals (PC's) composed of lossy dielectric rods in air were constructed with a microwave bandgap between 4-8 GHz. Fabry-Perot resonators of varying length were constructed from two of these PC' ...
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Journal ArticleApplied Physics Letters · July 5, 1999
A large variation in the dispersion data for AlxGa1.0-xN epitaxial layers is presented. An experimental study is conducted which no(λ) and ne(λ) were measured to an accuracy of approximately ±0.01 for five AlxGa1.0-xN MOCVD-grown layers on sapphire substra ...
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Journal Article · January 1, 1995
This chapter discusses rotational energy transfer (RET) in small polyatomic molecules. It focuses on incoherent state-to-state rates that result from collisions between like molecules and on the relationship of these rates to fundamental molecular paramete ...
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Journal ArticleMolecular Physics · August 10, 1993
The temperature dependencies of two fast vibrational energy transfer processes in methyl fluoride (CH3F) have been measured between 120K and 400 K by means of time-resolved millimetre/submillimetre-infrared double resonance spectroscopy. The first of these ...
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Journal ArticleJournal of Molecular Spectroscopy · January 1, 1992
Motivated by Oka's early work on molecular collisions and especially collision-induced rotational transitions, this paper addresses progress in these areas. Particular attention is paid to recent extensions to lower energy collisions of astrophysical signi ...
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Journal ArticleApplied Physics Letters · December 1, 1990
Direct measurements of the gain profile of optically pumped far-infrared lasers show that large shifts in the laser frequency can be caused by the absorption from thermal molecules on the laser transition. The absorption shifting greatly exacerbates pump f ...
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Journal ArticleThe Journal of Chemical Physics · January 1, 1990
We report the measurement of the rates of ΔJ=n, ΔK=0(|n| ≤ 10) processes for CH3F-CH3F collisions at 300 K. The data are derived from a time-resolved millimeter/ submillimeter-infrared double resonance investigation of both the 12CH3F and the 13CH3F isotop ...
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Journal ArticleThe Journal of Chemical Physics · January 1, 1989
Rotational energy transfer processes into the A and E symmetry species of the symmetric top molecule 13CH3F have been studied. In this time-resolved double resonance experiment a tunable millimeter/ submillimeter wave spectrometer was used to monitor the c ...
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ConferenceConference Digest - International Conference on Infrared and Millimeter Waves · December 1, 1987
A small-diameter continuous-wave far-infrared (FIR) laser that can provide approximately 100-MHz spectrally pure tunability has been developed and studied both experimentally and theoretically. Operation of this laser at pressures significantly greater tha ...
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ConferenceConference Digest - International Conference on Infrared and Millimeter Waves · December 1, 1987
Optically pumped far-infrared (OPFIR) lasers have been the subject of extensive theoretical and experimental investigations. The authors have used the results of a large experimental data set to appropriately select the degrees of freedom for a numerical s ...
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ConferenceConference Digest - International Conference on Infrared and Millimeter Waves · December 1, 1987
The authors conducted a time-resolved double-resonance study of **1**3CH//3F to explore the rotational and vibrational energy-transfer processes in this optically pumped far-infrared (OPFIR) laser. The use of a Q-switched CO//2 laser and sensitive, tunable ...
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Conference · January 1, 1987
A program of diagnostic studies and theoretical modeling has resulted in development of a tunable optically pumped far-infrared (FIR) laser that is very compact. The tunability of this laser comes about because it operates at pressures significantly higher ...
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Journal ArticleIEEE Journal of Quantum Electronics · January 1, 1987
A numerical simulation of collisional energy transfer in optically pumped far-infrared (OPFIR) lasers is presented along with a discussion of each collisional process and how it affects laser operation. A simulation is required to adequately describe these ...
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Journal ArticleApplied Physics Letters · December 1, 1986
We report the development of an ultrasmall, optically pumped cw far-infrared (FIR) laser that provides substantial tunability. This laser operates at pressures significantly higher than the maximum allowed by currently accepted theory. We also report the d ...
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