Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Series

Portland State University

Discipline
Keyword
Publication Year
Publication

Articles 1 - 30 of 362

Full-Text Articles in Physics

Electromagnetic Reciprocity In The Presence Of Topological Insulators, Huai-Yi Xie, P. T. Leung Sep 2020

Electromagnetic Reciprocity In The Presence Of Topological Insulators, Huai-Yi Xie, P. T. Leung

Physics Faculty Publications and Presentations

Electromagnetic reciprocity is studied in the presence of topological insulators (TI) with application of axion electrodynamics for harmonic electromagnetic fields. The corresponding generalized Lorentz and Feld-Tai type lemmas are derived in terms of the axion coupling parameter, and their correlation to the conditional symmetry in source-observer coordinates for the various Green dyadics is established subjected to different types of boundary conditions. Possible application of the results to the probing of the topological magneto-electric effects from TI is discussed.


A New Look At The Quantum Liouville Theorem, P. T. Leung, G. I. Ni Aug 2020

A New Look At The Quantum Liouville Theorem, P. T. Leung, G. I. Ni

Physics Faculty Publications and Presentations

We clarify certain confusions in the literature of the density operator in quantum mechanics, and demonstrate that the quantum Liouville theorem has the same form in both the Schrodinger and the Heisenberg pictures. Our starting point is to treat the density operator as an observable which has its specific time dependence in each of the two pictures. It is further shown that such a formulation will provide the exact correspondence between classical and quantum statistical mechanics with the Liouville theorem being interpreted as a conservation law, which is derivable from the equation of motion only in the quantum case.


Improving The Understanding Of Jet Grooming In Perturbation Theory, Andrew J. Larkoski Jun 2020

Improving The Understanding Of Jet Grooming In Perturbation Theory, Andrew J. Larkoski

Portland Institute for Computational Science Publications

Jet grooming has emerged as a necessary and powerful tool in a precision jet physics program. In this paper, we present three results on jet grooming in perturbation theory, focusing on heavy jet mass in e+e → hadrons collisions, groomed with the modified mass drop tagger. First, we calculate the analytic cross section at leading-order. Second, using the leading-order result and numerical results through next-to-next-to-leading order, we show that cusps in the distribution on the interior of phase space at leading-order are softened at higher orders. Finally, using analytic and numerical results, we show that terms that violate the assumptions ...


Analytical Results For The Three-Body Radiative Attachment Rate Coefficient, With Application To The Positive Antihydrogen Ion H¯+, Jack C. Straton Apr 2020

Analytical Results For The Three-Body Radiative Attachment Rate Coefficient, With Application To The Positive Antihydrogen Ion H¯+, Jack C. Straton

Physics Faculty Publications and Presentations

To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient αRA for producing the negative hydrogen ion H or its antimatter equivalent, the positive antihydrogen ion H¯+ , we found the analytic form for this integral. This procedure is useful for temperatures below 700 K, the region for which the production of H¯+ has potential use as an intermediate stage in the cooling of antihydrogen to ultra-cold (sub-mK) temperatures for spectroscopic studies and probing the gravitational interaction of the anti-atom. Our results, utilizing a 50-term explicitly correlated exponential ...


Groomed Jet Mass At High Precision, Adam Kardos, Andrew J. Larkoski, Zoltán Trócsányi Feb 2020

Groomed Jet Mass At High Precision, Adam Kardos, Andrew J. Larkoski, Zoltán Trócsányi

Portland Institute for Computational Science Publications

We present predictions of the distribution of groomed heavy jet mass in electron-positron collisions at the next-to-next-to-leading order accuracy matched with the resummation of large logarithms to next-to-next-to-next-to-leading logarithmic accuracy. Resummation at this accuracy is possible through extraction of necessary two-loop constants and three-loop anomalous dimensions from fixed-order codes.


Predicting Densities And Elastic Moduli Of Sio2-Based Glasses By Machine Learning, Yong-Jie Hu, Ge Zhao, Mingfei Zhang, Bin Bin, Tyler Del Rose, Qian Zhao, Qan Zu, Yang Chen, Xuekun Sun, Maarten De Jong, Multiple Additional Authors Jan 2020

Predicting Densities And Elastic Moduli Of Sio2-Based Glasses By Machine Learning, Yong-Jie Hu, Ge Zhao, Mingfei Zhang, Bin Bin, Tyler Del Rose, Qian Zhao, Qan Zu, Yang Chen, Xuekun Sun, Maarten De Jong, Multiple Additional Authors

Mathematics and Statistics Faculty Publications and Presentations

Chemical design of SiO2-based glasses with high elastic moduli and low weight is of great interest. However, it is difficult to find a universal expression to predict the elastic moduli according to the glass composition before synthesis since the elastic moduli are a complex function of interatomic bonds and their ordering at different length scales. Here we show that the densities and elastic moduli of SiO2-based glasses can be efficiently predicted by machine learning (ML) techniques across a complex compositional space with multiple (>10) types of additive oxides besides SiO2. Our machine learning approach relies on a training set generated ...


Polarization In The Production Of The Antihydrogen Ion, Casey A. Yazejian, Jack C. Straton Jan 2020

Polarization In The Production Of The Antihydrogen Ion, Casey A. Yazejian, Jack C. Straton

Physics Faculty Publications and Presentations

We provide estimates of both the cross section and rate coefficient for the radiative attachment of a second positron to create the H̅+ ion, H̅(1s)+e+→H̅+(1s2 1Se)+ℏω, for which the polarization of the initial state H̅(1s) is taken into account. We show how to analytically integrate the resulting six-dimensional, three-body integrals for wave functions composed of explicitly correlated exponentials, a result that may be extended to Hylleraas wave functions. We extend Bhatia’s polarization results for the equivalent matter problem down to the low temperatures required for the Gravitational ...


Reducing A Class Of Two-Dimensional Integrals To One-Dimension With An Application To Gaussian Transforms, Jack C. Straton Jan 2020

Reducing A Class Of Two-Dimensional Integrals To One-Dimension With An Application To Gaussian Transforms, Jack C. Straton

Physics Faculty Publications and Presentations

Quantum theory is awash in multidimensional integrals that contain exponentials in the integration variables, their inverses, and inverse polynomials of those variables. The present paper introduces a means to reduce pairs of such integrals to one dimension when the integrand contains powers multiplied by an arbitrary function of xy/ (x + y) multiplying various combinations of exponentials. In some cases these exponentials arise directly from transition-amplitudes involving products of plane waves, hydrogenic wave functions, and Yukawa and/or Coulomb potentials. In other cases these exponentials arise from Gaussian transforms of such functions.


Enhancing Final Image Contrast In Off-Axis Digital Holography Using Residual Fringes, Manuel Bedrossian, Kent Wallace, Eugene Serabyn, Chris Lindensmith, Jay Nadeau Jan 2020

Enhancing Final Image Contrast In Off-Axis Digital Holography Using Residual Fringes, Manuel Bedrossian, Kent Wallace, Eugene Serabyn, Chris Lindensmith, Jay Nadeau

Physics Faculty Publications and Presentations

We show that background fringe-pattern subtraction is a useful technique for removing static noise from off-axis holographic reconstructions and can enhance image contrast in volumetric reconstructions by an order of magnitude in the case for instruments with relatively stable fringes. We demonstrate the fundamental principle of this technique and introduce some practical considerations that must be made when implementing this scheme, such as quantifying fringe stability. This work also shows an experimental verification of the background fringe subtraction scheme using various biological samples.


Characterization Of Retinol Stabilized In Phosphatidylcholine Vesicles With And Without Antioxidants, Yekaterina G. Chmykh, Jay Nadeau Jan 2020

Characterization Of Retinol Stabilized In Phosphatidylcholine Vesicles With And Without Antioxidants, Yekaterina G. Chmykh, Jay Nadeau

Physics Faculty Publications and Presentations

Retinol stability has been reported to be improved by encapsulation in liposomes, both with and without cholesterol. However, this improvement is limited because of lipid peroxidation. In this study, we compare the stability of retinol in phosphatidylcholine liposomes under ultraviolet (UV) light or standard room air, with and without the addition of antioxidants. Both butylated hydroxytoluene (BHT) and a proprietary mix (StoppOx) improved the shelf stability from vesicles, including within the aqueous layer. Fluorescence lifetimes were equally heterogeneous. Under UV irradiation, StoppOx protected retinol for significantly longer than BHT and via different mechanisms. This suggests that natural antioxidants work well ...


Topological Magnetoelectric Effect As Probed By Nanoshell Plasmonic Modes, Railing Chang, Huai Yi Xie, Ya-Chih Wang, Hai-Pang Chiang, P.T. Leung Dec 2019

Topological Magnetoelectric Effect As Probed By Nanoshell Plasmonic Modes, Railing Chang, Huai Yi Xie, Ya-Chih Wang, Hai-Pang Chiang, P.T. Leung

Physics Faculty Publications and Presentations

Axion electrodynamics is applied to study the response of a plasmonic nanoshell with a core made of topological insulator (TI) materials. The electric polarizability of such a system is calculated in the long wavelength limit via the introduction of two scalar potentials satisfying the various appropriate boundary conditions. Our focus is on the topological magneto-electric effect (TME) as manifested in the coupled plasmonic resonances of the nanoshell. It is found that for a TI with broken time-reversal symmetry, such TME will lead to observable red-shifts in the coupled plasmonic modes, with more significant manifestation of such shifts for the bonding ...


Adapting Realtime Physics For Distance Learning With The Iolab, Erik Bodegom, Erik Jensen, David Sokoloff Sep 2019

Adapting Realtime Physics For Distance Learning With The Iolab, Erik Bodegom, Erik Jensen, David Sokoloff

Physics Faculty Publications and Presentations

The IOLab is a versatile and inexpensive data acquisition device in a cart that can roll on its three wheels. It has numerous sensors for a variety of physical quantities. We adapted RealTime Physics, Module 1: Mechanics active learning labs for use with the IOLab. We tested these labs both on campus and with distance learners at Portland State University and Chemeketa Community College for three years, consistently obtaining significant conceptual learning gains on the Force and Motion Conceptual Evaluation (FMCE). Student attitudes towards the labs, the device, and distance learning—as measured by post-course evaluations—were generally very positive.


The Fourier Spectrum Of A Singing Wine Glass, Reuben Leatherman, Justin Charles Dunlap, Ralf Widenhorn Aug 2019

The Fourier Spectrum Of A Singing Wine Glass, Reuben Leatherman, Justin Charles Dunlap, Ralf Widenhorn

Physics Faculty Publications and Presentations

The phenomenon of the singing wineglass is familiar to many. Most people have run a finger along the rim of a wine glass with the right speed and pressure to get it to whistle a tone or perhaps heard a glass harmonica being played. However, have you ever noticed and wondered why the vibrations caused by a finger on a glass produce a pulsating sound, rather than a steady, constant-amplitude vibration? Further exploration reveals that the sound and pulsations of a wine glass vary depending on the way the wine glass is stimulated. In this paper, we investigate and model ...


Multiwavelength Digital Holographic Imaging And Phase Unwrapping Of Protozoa Using Custom Fiji Plug-Ins, David Cohoe, Iulia Hanczarek, J. Kent Wallace, Jay Nadeau Jul 2019

Multiwavelength Digital Holographic Imaging And Phase Unwrapping Of Protozoa Using Custom Fiji Plug-Ins, David Cohoe, Iulia Hanczarek, J. Kent Wallace, Jay Nadeau

Physics Faculty Publications and Presentations

Multiwavelength digital holographic microscopy (DHM) has been used to improve phase reconstructions of digital holograms by reducing 2p phase ambiguities. However, most samples used as test images have been solid or adhered to a surface, making it easy to determine focal planes and correct for chromatic aberration. In this study we apply 3-wavelength off-axis DHM to swimming protozoa containing distinct spectral features such as chlorophyll and carotenoids. We reconstruct the holograms into amplitude and phase images using the angular spectrum method. Methods for noise subtraction, chromatic aberration correction, and image registration are presented for both amplitude and phase. Approaches to ...


On Classification Approaches For Crystallographic Symmetries Of Noisy 2d Periodic Patterns, Peter Moeck May 2019

On Classification Approaches For Crystallographic Symmetries Of Noisy 2d Periodic Patterns, Peter Moeck

Physics Faculty Publications and Presentations

The existing types of classification approaches for the crystallographic symmetries of patterns that are more or less periodic in two dimensions (2D) are reviewed. Their relative performance is evaluated in a qualitative manner. Pseudo-symmetries of different kinds are discussed as they present severe challenges to most classification approaches when noise levels are moderate to high. The author’s information theory based approaches utilize digital images and geometric Akaike Information Criteria. They perform well in the presence of pseudo-symmetries and turn out to be the only ones that allow for fully objective (completely researcher independent) and generalized noise level dependent classifications ...


Sound Propagation, Reflection, And Its Relevance To Ultrasound Imaging, Thomas Allen, Alex Chally, Bradley Moser, Ralf Widenhorn Mar 2019

Sound Propagation, Reflection, And Its Relevance To Ultrasound Imaging, Thomas Allen, Alex Chally, Bradley Moser, Ralf Widenhorn

Physics Faculty Publications and Presentations

The labs presented here build on a simple speed of sound activity and models medical ultrasound imaging by demonstrating how multiple reflections propagate in a closed system. A short sound pulse is emitted into a pipe that is closed at one end and contains one or more partially reflecting surfaces within the pipe. The variety of reflections and transmissions that occur can be measured with a microphone at the pipe entrance.


Viscosities, Diffusion Coefficients, And Mixing Times Of Intrinsic Fluorescent Organic Molecules In Brown Limonene Secondary Organic Aerosol And Tests Of The Stokes–Einstein Equation, Dagny A. Ullmann, Mallory L. Hinks, Adrian M. Maclean, Christopher Butenhoff, James W. Grayson, Kelley Barsanti, Jose L. Jimenez, Sergey A. Nizkorodov, Saeid Kamal, Allan K. Bertram Feb 2019

Viscosities, Diffusion Coefficients, And Mixing Times Of Intrinsic Fluorescent Organic Molecules In Brown Limonene Secondary Organic Aerosol And Tests Of The Stokes–Einstein Equation, Dagny A. Ullmann, Mallory L. Hinks, Adrian M. Maclean, Christopher Butenhoff, James W. Grayson, Kelley Barsanti, Jose L. Jimenez, Sergey A. Nizkorodov, Saeid Kamal, Allan K. Bertram

Physics Faculty Publications and Presentations

Viscosities and diffusion rates of organics within secondary organic aerosol (SOA) remain uncertain. Using the bead-mobility technique, we measured viscosities as a function of water activity (aw) of SOA generated by the ozonolysis of limonene followed by browning by exposure to NH3 (referred to as brown limonene SOA or brown LSOA). These measurements together with viscosity measurements reported in the literature show that the viscosity of brown LSOA increases by 3–5 orders of magnitude as the aw decreases from 0.9 to approximately 0.05. In addition, we measured diffusion coefficients of intrinsic fluorescent organic molecules within ...


Photoemission Electron Microscopy To Characterize Slow Light In A Photonic Crystal Line Defect, Theodore Stedmark, Rolf Könenkamp Jan 2019

Photoemission Electron Microscopy To Characterize Slow Light In A Photonic Crystal Line Defect, Theodore Stedmark, Rolf Könenkamp

Physics Faculty Publications and Presentations

Using femtosecond nonlinear photoemission electron microscopy (PEEM) we provide a detailed characterization of slow light in a small-size asymmetric photonic crystal structure. We show that PEEM is capable of providing a unique description of the light propagation in such structures by direct imaging of the guided mode. This noninvasive characterization technique allows modal properties such as effective index, phase velocities, and group velocities to be determined. Combining experimental results with finite element method simulation calculations, we study slow light phenomena in a photonic crystal defect mode, and we produce a comprehensive picture of the mechanisms behind it. Our results illustrate ...


Imaging Technologies And Strategies For Detection Of Extant Extraterrestrial Microorganisms, Jay Nadeau, Manuel Bedrossian, Chris Lindensmith Jan 2019

Imaging Technologies And Strategies For Detection Of Extant Extraterrestrial Microorganisms, Jay Nadeau, Manuel Bedrossian, Chris Lindensmith

Physics Faculty Publications and Presentations

There is no reductionist definition of life, so the way organisms look, behave, and move is the most definitive way to identify extraterrestrial life. Life elsewhere in the Solar System is likely to be microbial, but no microscope capable of imaging prokaryotic life has ever flown on a lander mission to a habitable planet. Nonetheless, high-resolution microscopes have been developed that are appropriate for planetary exploration. Traditional light microscopy, interferometric microscopy, light-field microscopy, scanning probe microscopy, and electron microscopy are all possible techniques for the detection of extant micro-organisms on Mars and the moons of Jupiter and Saturn. This article ...


Instrumentation-Level Improvements In Shear-Force Near-Field Acoustic Microscopy, J. Bai, P. Devulapalli, Theodore Brockman, Andres H. La Rosa Dec 2018

Instrumentation-Level Improvements In Shear-Force Near-Field Acoustic Microscopy, J. Bai, P. Devulapalli, Theodore Brockman, Andres H. La Rosa

Physics Faculty Publications and Presentations

The recently introduced Shear-force Near-field Acoustic Microscopy (SANM) brings a new sensing mechanism to the scanning probe microscopy family. SANM's ability to simultaneously monitor, in real time, several physical sample's responses presents some challenges for ensuring optimal operation; namely, avoid "cross-talk" among the multiple signals, address the compensation of thermal drift to ensure reproducibility of the measurements, and measuring the typical low-level signals obtained from nanometer-sized tested regions. Here, several improvements relevant to SANM, but valid for SPM in general, are addressed. i) The probe's coarse approach is performed via stepper motors, which are controlled either by ...


High-Performance Self-Powered Uv Detector Based On Sno2-Tio2 Nanomace Arrays, Duo Chen, Lin Wei, Lingpan Meng, Yanxue Chen, Yufeng Tian, Shishen Yan, Liangmo Mei, Jun Jiao Dec 2018

High-Performance Self-Powered Uv Detector Based On Sno2-Tio2 Nanomace Arrays, Duo Chen, Lin Wei, Lingpan Meng, Yanxue Chen, Yufeng Tian, Shishen Yan, Liangmo Mei, Jun Jiao

Physics Faculty Publications and Presentations

Photoelectrochemical cell-typed self-powered UV detectors have attracted intensive research interest due to their low cost, simple fabrication process, and fast response. In this paper, SnO2-TiO2 nanomace arrays composed of SnO2 nanotube trunk and TiO2 nanobranches were prepared using soft chemical methods, and an environment-friendly self-powered UV photodetector using this nanostructure as the photoanode was assembled. Due to the synergistic effect of greatly accelerated electron-hole separation, enhanced surface area, and reduced charge recombination provided by SnO2-TiO2 nanomace array, the nanostructured detector displays an excellent performance over that based on bare SnO2 arrays. The impact of the growing time of TiO2 branches ...


Combining Atomic Force Microscopy And Shear-Force Acoustic Near-Field Microscopy To Characterize Confined Mesoscopic Fluids, Monte Allen Kozell, Theodore Brockman, Andres H. La Rosa Dec 2018

Combining Atomic Force Microscopy And Shear-Force Acoustic Near-Field Microscopy To Characterize Confined Mesoscopic Fluids, Monte Allen Kozell, Theodore Brockman, Andres H. La Rosa

Physics Faculty Publications and Presentations

An atomic force microscopy (AFM) cantilever is integrated into to a quartz tuning fork (QTF) to probe the viscoelastic properties of mesoscopic fluid layers confined between two solid surfaces under shear. Two procedures to fabricate the AFM/QTF probe are described herein. In the first, a nano-manipulator is used to transport a commercially available afm cantilever from its chip holder to the edge of a QTF tine. In the second, an afm cantilever is fabricated at the edge of the QTF tine itself. In both cases we exploit the capabilities of a dual-beam system (focused ion beam/scanning electron microscope ...


Confined Fluid Analyzed With Near-Field Acoustic Detection, Rodolfo Fernandez Rodriguez, Theodore Brockman, J. Bai, Andres H. La Rosa Dec 2018

Confined Fluid Analyzed With Near-Field Acoustic Detection, Rodolfo Fernandez Rodriguez, Theodore Brockman, J. Bai, Andres H. La Rosa

Physics Faculty Publications and Presentations

Measurement of the damping and elastic interactions between two solids interfaces (one being the apex of a tapered probe that is attached to one tine of a quartz tuning fork while the other is a flat substrate) under relative lateral oscillatory motion are reported. The solid boundaries are separated by a nanometer sized gap, and emphasis is placed on the role played by the mesoscopic fluid trapped in between. The measurements were implemented using two new acoustic techniques that have been integrated into a tuning fork based scanning probe microscope; the whole metrology system offers sub-nanometer precision for controlling the ...


Finite Element Method Analysis Of Whispering Gallery Acoustic Sensing, T. Le, H. Tran, Rodolfo Fernandez Rodriguez, C.J. Solano Salinas, Nima Laal, R. Bringas, J. Quispe, F. Segundo, Andres H. La Rosa Dec 2018

Finite Element Method Analysis Of Whispering Gallery Acoustic Sensing, T. Le, H. Tran, Rodolfo Fernandez Rodriguez, C.J. Solano Salinas, Nima Laal, R. Bringas, J. Quispe, F. Segundo, Andres H. La Rosa

Physics Faculty Publications and Presentations

Whispering Gallery Acoustic Sensing (WGAS) has recently been introduced as a sensing feedback mechanism to control the probe-sample separation distance in scanning probe microscopy that uses a quartz tuning fork as a sensor (QTF-SPM). WGAS exploits the SPM supporting frame as a resonant acoustic cavity to monitor the nanometer-sized amplitude of the QTF oscillations. Optimal WGAS sensitivity depends on attaining an exact match between the cavity's frequency peak response and the TF resonance frequency. However, two aspects play against this objective: i) the unpredictable variability of the TF resonance frequency (upon attaching a SPM-probe to one of its tines ...


Probe Damage Evaluation In Frequency-Modulation Shear-Force Acoustic Near-Field Microscopy, Theodore Brockman, Rodolfo Fernandez Rodriguez, J. Bai, Monte Allen Kozell, Andres H. La Rosa Dec 2018

Probe Damage Evaluation In Frequency-Modulation Shear-Force Acoustic Near-Field Microscopy, Theodore Brockman, Rodolfo Fernandez Rodriguez, J. Bai, Monte Allen Kozell, Andres H. La Rosa

Physics Faculty Publications and Presentations

Shear-force acoustic near-field microscopy (SANM) and Whispering Gallery Acoustic Sensing have recently been introduced as a tandem system to characterize the viscoelastic response of fluids confined between two solid-boundaries in relative oscillatory lateral motion. SANM uses a) a laterally oscillating tapered probe (attached to a quartz tuning fork QTF) as one of the trapping boundaries, and b) an acoustic sensor (attached to the other flat-substrate boundary) that independently monitors the fluid’s acoustic emission. On the other and, WGAS is another technique that uses an acoustic transducer (attached to the frame holding the probe) to monitor the probe’s lateral ...


Supercanonical Probability Distributions, John D. Ramshaw Aug 2018

Supercanonical Probability Distributions, John D. Ramshaw

Physics Faculty Publications and Presentations

The canonical probability distribution describes a system in thermal equilibrium with an infinite heat bath. When the bath is finite the distribution is modified. These modifications can be derived by truncating a Taylor-series expansion of the entropy of the heat bath, but their form depends on the expansion parameter chosen. We consider two such expansions, which yield supercanonical (i.e., higher-order canonical) distributions of exponential and power-law form. The latter is identical in form to the "Tsallis distribution," which is therefore a valid asymptotic approximation for an arbitrary finite heat bath, but bears no intrinsic relation to Tsallis entropy.


Entanglement Entropy, Dualities, And Deconfinement In Gauge Theories, Mohamed M. Anber, Benjamin J. Kolligs Aug 2018

Entanglement Entropy, Dualities, And Deconfinement In Gauge Theories, Mohamed M. Anber, Benjamin J. Kolligs

Portland Institute for Computational Science Publications

Computing the entanglement entropy in confining gauge theories is often accompanied by puzzles and ambiguities. In this work we show that compactifying the theory on a small circle S 1/L evades these difficulties. In particular, we study Yang-Mills theory on R3×S 1/L with double-trace deformations or adjoint fermions and hold it at temperatures near the deconfinement transition. This theory is dual to a multi-component (electric-magnetic) Coulomb gas that can be mapped either to an XY-spin model with Zp symmetry-preserving perturbations or dual Sine-Gordon model. The entanglement entropy of the dual SineGordon model exhibits an extremum ...


Structural Instability And Dynamic Emission Fluctuations In Zinc Oxide Random Lasers, Zachariah Peterson, Robert Campbell Word, Rolf Könenkamp Aug 2018

Structural Instability And Dynamic Emission Fluctuations In Zinc Oxide Random Lasers, Zachariah Peterson, Robert Campbell Word, Rolf Könenkamp

Physics Faculty Publications and Presentations

We report experimental results on the structural stability of optically pumped zinc oxide random lasers. We find that the lasing threshold is not entirely stable and depends on the accumulated light exposure received in pulsed optical pumping. We show that exposure levels below ∼1.5 kJ/cm2 improve the lasing efficiency and lower the lasing threshold. Beyond that value, however, lasing efficiency and threshold begin to degrade. Electron microscopy shows that the degradation is accompanied by morphological changes characteristic of melting. These changes become visible at an exposure of ∼0.7 kJ/cm2. We suggest that the melting is initially ...


Enhanced Terahertz Emission From Quantum Dot By Graphene-Coated Nanoparticle, Edin Sijercic, P. T. Leung Jul 2018

Enhanced Terahertz Emission From Quantum Dot By Graphene-Coated Nanoparticle, Edin Sijercic, P. T. Leung

Physics Faculty Publications and Presentations

The terahertz (THz) emission from quantum dots in close proximity to graphene-coated nanoparticles is studied via phenomenological modeling with particular interest in the possibility of enhancement for such emission via the excitation of the graphene plasmons. It is shown that depending on various factors such as the damping factor and the Fermi level of the graphene, as well as the size and core material of the coated particle, such plasmonic-enhanced THz emission is indeed possible. This thus opens up a new pathway to provide intense THz sources for future applications.


Steady States And Transport Processes In Urban Ozone Balances, M. A. K. Khalil Jul 2018

Steady States And Transport Processes In Urban Ozone Balances, M. A. K. Khalil

Physics Faculty Publications and Presentations

Core chemical theory is combined with transport processes and local emissions to study the validity of commonly made assumptions regarding steady states to interpret urban and regional ozone data. It is shown that photo-stationary states of NO and NO2 cannot exist in urban areas or polluted regions in addition to the lack of such a state for ozone. Calculations in published papers, which make the assumption of a photo-stationary state for NO and NO2, or ozone, are likely to be inaccurate by unacceptable amounts. The Leighton Ratio is re-interpreted to show how it incorporates both the peroxy radical and transport ...