Physical Sciences and Mathematics Commons^™

Model For A Partially Coherent Gaussian Beam In Atmospheric Turbulence With Application In Lasercom, Olga Korotkova, Larry C. Andrews, Ronald L. Phillips

Physics Articles and Papers

Analytic expressions for the mutual coherence function (MCF) and the scintillation index of a partially coherent lowest order Gaussian beam wave propagating through the atmosphere (based on Kolmogorov spectrum model) are developed for the pupil plane of a receiving system. Partial coherence of the beam is modeled as a thin (complex) phase screen with Gaussian spectrum (Rytov theory and ABCD ray matrices are applied). The relation between the second- and fourth-order statistics for a beam with any degree of coherence in the atmosphere is introduced with the help of “effective” beam parameters, deduced from the free-space MCF. In particular, the …

Non-Degenerate Normal-Mode Doublets In Vibrating Flat Circular Plates, Bradley M. Deutsch, Alexandra R. Robinson, Richard J. Felce, Thomas R. Moore

Student-Faculty Collaborative Research Publications

The vibrations of flat circular plates have been studied for hundreds of years, and they are well understood by the scientific community. Unfortunately, when vibrating circular plates are discussed in textbooks, the relationship between pairs of spatially orthogonal vibrational patterns that occur at each of the normal-mode frequencies is often ignored. Usually these orthogonal solutions are presented to the student as being degenerate in frequency; however, in practice the degeneracy of the doublet is often broken and the two spatially orthogonal solutions are separated in frequency. We show theoretically and experimentally that the degeneracy can be broken by a small …

Effect Of Measurement On The Periodicity Of The Coulomb Staircase Of A Superconducting Box, Jaan Männik, J. E. Lukens

Jaan Männik

We report on the effect of the backaction of a single Cooper pair transistor electrometer (E) on the charge state of a superconducting box (B). The charge is e periodic in the gate bias of B when E is operated near voltages 2Δ/e or 4Δ/e. We show that this is due to quasiparticle poisoning of B at a rate proportional to the number of quasiparticle tunneling events in E per second. We are able to eliminate this backaction and recover 2e-charge periodicity using a new measurement method based on switching-current modulation of E.

URL: http://link.aps.org/doi/10.1103/PhysRevLett.92.057004

DOI: 10.1103/PhysRevLett.92.057004

A Demonstration Of Phonons That Implements The Linear Theory, Dietrich Lüerßen, Nalini Easwar, Ayesha Malhotra, Libby Hutchins, Kim Schulze, Brandi Wilcox

Physics: Faculty Publications

Beads on a vibrating wire are used to simulate the discrete structure of a solid-state material. The novel idea of the experiment is to use very small oscillation amplitudes of the wire to avoid nonlinearities in the interaction. We achieve a good signal-to-noise ratio using a lock-in technique. We find quantitative agreement between theory and experiment for not only a mono- and a diatomic chain, but also for the bare wire. The latter agreement is the crucial aspect that distinguishes our experiment from previous ones. This agreement assures that the fundamental assumption of the theory ~Hooke’s law! is satisfied. We …

On The Solar Wind Control Of Cusp Aurora During Northward Imf, M. G. Bobra, S. M. Petrinec, S. A. Fuselier, E. S. Claflin, Harlan E. Spence

Physics & Astronomy

[1] The location of cusp aurora during northward interplanetary magnetic field (IMF) conditions and the solar wind control of that location are explored. The cusp aurora is imaged by the Imager for Magnetopause-to-Aurora Global Exploration's (IMAGE) Far Ultraviolet Instrument (FUV). Predicted locations of the cusp aurora were computed by assuming anti-parallel reconnection between the observed IMF orientation and the 1996 Tsyganenko model magnetopause magnetic field. While the majority of anti-parallel reconnection sites tailward of the cusp, when mapped to the ionosphere, coincide with the observed cusp aurora, the anti-parallel merging hypothesis cannot explain certain aspects of the observations, including its …

The Surface Band Structure Of W(112), Yaroslav B. Losovyj, I. N. Yakovkin, Hae-Kyung Jeong, Peter A. Dowben

Peter Dowben Publications

Both the experimental and theoretical band structure of the W(112) surface are presented, with the theoretical band structure calculated by the film–LAPW (linearized augmented plane waves) method. The results permit one to compare the W(112) and Mo(112) band structures and illuminate the similarities. It is found that for the W(112) surface the main photoemission features combine contributions from both the surface and bulk, as has been previously noted for Mo(112). The main differences between the electronic structures of the furrowed W(112) and Mo(112) surfaces are seen in the width of occupied bands. The differences are attributed to the extent of …

Chaos-Induced Pulse Trains In The Ionization Of Hydrogen, K. A. Mitchell, J. P. Handley, B. Tighe, A. Flower, John B. Delos

Arts & Sciences Articles

We predict that a hydrogen atom in parallel electric and magnetic fields, excited by a short laser pulse to an energy above the classical saddle, ionizes via a train of electron pulses. These pulses are a consequence of classical chaos induced by the magnetic field. We connect the structure of this pulse train (e.g., pulse size and spacing) to fractal structure in the classical dynamics. This structure displays a weak self-similarity, which we call “epistrophic self-similarity.” We demonstrate how this self-similarity is reflected in the pulse train.

High-Quality, Melt-Grown Zno Single Crystals, D. C. Reynolds, C. W. Litton, David C. Look, J. E. Joelscher, B. Claflin, T. C. Collins, J. Nause, B. Nemeth

Physics Faculty Publications

High-quality, melt-grown ZnO crystals are reported. The reflection and emission spectra of the melt-grown samples are compared with the same spectra from high-quality, vapor-grown ZnO crystals. We isolate the reflection and emission spectra predominantly related to the intrinsic properties associated with the wurtzite structure of the crystals. The quality of the crystals is reflected in the spectral reproduction of the intrinsic properties of the crystals. Both the ground state and the n=2 state of the free excitons associated with the A, B, and C valence bands of the crystals are spectrally observed in reflection. Assuming a hydrogenic character for …

Application Of Photopolymer Holographic Gratings, Emilia Mihaylova, Izabela Naydenova, Hosam Sherif, Suzanne Martin, Vincent Toal

Conference Papers

Two optical set-ups for electronic speckle pattern shearing interferometry (ESPSI) using photopolymer diffractive optical elements are presented. Holographic gratings are recorded using an acrylamide based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. In both ESPSI systems the photopolymer gratings are used to shear the image. In the first ESPSI system only one grating is used in combination with a sheet of ground glass. The distance between the grating and the ground glass can be used to control the amount of the shear. The sheared images on the ground glass …

The Case For An Optically-Thick High-Velocity Broad-Line Region, Stephanie A. Snedden, C. Martin Gaskell

Department of Physics and Astronomy: Faculty Publications

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Lyα/Hα ratio in the high-velocity gas. We show that the suggestion that the high velocity gas is optically-thin presents many problems. We show that the relative strengths of the high velocity wings arise naturally in an optically-thick BLR component. An optically-thick model successfully explains the equivalent widths of the lines, the Lyα/Hα ratios and flatter Balmer decrements in …

Statistical Study Of Solar Radio Bursts, Gelu-Marius Nita

Dissertations

The peak flux distribution of 40 years of solar radio burst data recorded by NOAA, as a function of frequency and time over a wide range of frequencies, was investigated to quantify the potential impact of radio bursts on wireless systems. Tables of fit parameters, which can be used to find burst occurrence rates in a number of frequency ranges, are presented. The typical power-law index of number density distribution, -1.8, is similar to that found in many hard X-ray studies. Significant changes were found in power-law index with frequency. The results may be useful for designers of current and …

High Resolution Solar Observations In The Context Of Space Weather Prediction, Guo Yang

Dissertations

Space weather has a great impact on the Earth and human life. It is important to study and monitor active regions on the solar surface and ultimately to predict space weather based on the Sun's activity. In this study, a system that uses the full power of speckle masking imaging by parallel processing to obtain high-spatial resolution images of the solar surface in near real-time has been developed and built. The application of this system greatly improves the ability to monitor the evolution of solar active regions and to predict the adverse effects of space weather. The data obtained by …

State-To-State Rotational Relaxation Rate Constants For Co+Ne From Ir-Ir Double-Resonance Experiments: Comparing Theory To Experiment, David A. Hostutler, Tony C. Smith, Gordon D. Hager, George C. Mcbane, Michael C. Heaven

Peer Reviewed Articles

IR-IR double-resonance experiments were used to study the state-to-state rotational relaxation of CO with Ne as a collision partner. Rotational levels in the range J_i=2-9 were excited and collisional energy transfer of population to the levels J_f=2-8 was monitored. The resulting data set was analyzed by fitting to numerical solutions of the master equation. State-to-state rate constant matrices were generated using fitting law functions. Fitting laws based on the modifed exponential gap (MEG) and statistical power exponential gap (SPEG) models were used; the MEG model performed better than the SPEG model. A rate constant matrix was …

Limits To Performance Improvement Provided By Balanced Interferometers And Balanced Detection In Oct/Ocm Instruments, David Liao, Adam E. Pivonka, Brendan R. Haberle, Daniel C. Petersen, Barbara M. Hoeling, Richard C. Haskell

All HMC Faculty Publications and Research

We compare the dynamic range of OCT/OCM instruments configured with unbalanced interferometers, e.g., Michelson interferometers, with that of instruments utilizing balanced interferometers and balanced photodetection. We define the dynamic range (DR) as the ratio of the maximum fringe amplitude achieved with a highly reflecting surface to the root-mean-square (rms) noise. Balanced systems achieve a dynamic range 2.5 times higher than that of a Michelson interferometer, enabling an image acquisition speed roughly 6 times faster. This maximum improvement occurs at light source powers of a few milliwatts. At light source powers higher than 30 mW, the advantage in acquisition speed of …

Measurement Of The Average Time-Integrated Mixing Probability Of B-Flavored Hadrons Produced At The Fermilab Tevatron, Darin Acosta, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have measured the number of like-sign (LS) and opposite-sign (OS) lepton pairs arising from double semileptonic decays of b and b-bar hadrons, pair produced at the Fermilab Tevatron collider. The data samples were collected with the Collider Detector at Fermilab during the 1992–1995 collider run by triggering on the existence of µµ or eµ candidates in an event. The observed ratio of LS to OS dileptons leads to a measurement of the average time-integrated mixing probability of all produced b-flavored hadrons which decay weakly, Χ̅=0.152±0.007 (stat)±0.011 (syst), that is significantly larger than the world average Χ̅=0.118±0.005.

Derivation Of Moving-Coil Loudspeaker Parameters Using Plane Wave Tube Techniques, Brian Eric Anderson

Theses and Dissertations

Small-signal moving-coil loudspeaker driver parameters are traditionally derived through electrical impedance measurement techniques. These parameters are commonly called Thiele/Small parameters, after Neville Thiele and Richard Small who are credited with developing industry-standard loudspeaker modeling techniques. However, because loudspeaker drivers are electro-mechano-acoustical transducers, it should be possible to measure their parameters in physical domains other than the electrical domain. A method of measuring loudspeaker parameters from the acoustical domain will be developed. The technique uses a plane wave tube to measure acoustical properties of a baffled driver under test. Quantities such as the transmission loss through the driver are measured for …

Quantum And Classical Coincidence Imaging, Ryan S. Bennink, Sean J. Bentley, Robert W. Boyd, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

Coincidence, or ghost, imaging is a technique that uses two correlated optical fields to form an image of an object. In this work we identify aspects of coincidence imaging which can be performed with classically correlated light sources and aspects which require quantum entanglement. We find that entangled photons allow high-contrast, high-resolution imaging to be performed at any distance from the light source. We demonstrate this fact by forming ghost images in the near and far fields of an entangled photon source, noting that the product of the resolutions of these images is a factor of 3 better than that …

High-Precision Lattice Qcd Confronts Experiment, James E. Hetrick, C. T. Davies

All Faculty Articles - School of Engineering and Computer Science

The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of “gold-plated” quantities. We find agreement to within statistical and systematic errors of 3% or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics.

Development Of A Fourier Transform-Based Time-Of-Flight Electron Spectrometer With Ultra-High Resolution, Brian Frederick, Peter H. Kleban

University of Maine Office of Research Administration: Grant Reports

This project, funded by the Major Research Instrumentation program, will develop a time-of-flight electron velocity analyzer using advanced modulation and Fourier deconvolution techniques with a throughput advantage on the order of 1000 over existing instruments. The new spectrometer will operate with ultra-high resolution in the energy range 1-1000 electron volts. It will be useful for the investigation of surface properties under ultra-high vacuum and a variety of other scientific and commercial applications. The device utilizes secondary chopping of the electron beam in the nanosecond or sub-nanosecond time regime, and state-of-the-art Fourier transform-based digital signal recovery methods. Additionally, there is potential …

Are Half-Metallic Ferromagnets Half Metals? (Invited), Peter A. Dowben, Ralph Skomski

Peter Dowben Publications

Several classes of materials are currently under investigation as potential high-spin-polarization materials. Unfortunately, the proposed half-metallic materials, including the semi-Heusler alloys, the manganese perovskites, and the "simpler" oxides such as chromium dioxide and magnetite, suffer from fundamental limitations. First, the postulated half-metallic systems lose their full (T = 0) spin polarization at finite temperatures and, second, surfaces, interfaces, and structural inhomogenities destroy the complete spin polarization of half-metallic systems even at zero temperature. In a strict sense, half-metallic ferromagnetism is limited to zero temperature since magnon and phonon effects lead to reductions in polarization at finite temperatures. ©2004 American Institute …

Superferromagnetic Domain State Dynamics In Discontinuous Cofe/Al2o3, Christian Binek

Christian Binek Publications

Magnetization hysteresis and AC susceptibility measurements were performed on the discontinuous metal–insulator multilayer [Co80Fe20(1.4 nm)/Al2O3(3 nm)]10. CoFe forms ferromagnetic single-previous domain term particles being embedded in the Al2O3 matrix. Due to strong dipolar inter-particle interactions a “previous superferromagnetic term” correlation of particle moments was previously stated. The dynamical magnetic properties of the superferromagnet can be understood in the framework of previous domain term wall motion in an impure ferromagnet. Kinetic simulations are employed, which are based on field and temperature-dependent previous domain term wall velocities. The magnetization hysteresis as well as the AC susceptibility, χ′−iχ′′, are calculated and compared to …

Water Absorption And Dielectric Changes In Crystalline Poly(Vinylidene Fluoride-Trifluoroethylene) Copolymer Films, P.A. Jacobson, Luis G. Rosa, Christina M. Othon, Kristin L. Kraemer, A.V. Sorokin, Stephen Ducharme, Peter A. Dowben

Peter Dowben Publications

Crystalline Langmuir–Blodgett copolymer films of vinylidene fluoride with trifluoroethylene (70%:30% and 80%:20%) absorb water. Water absorption is accompanied by film swelling, as indicated by an increase in lattice spacing, sometimes by as much as 5%. This water absorption, between 0 and 40 °C, is a result of intercalation or occupation of interstitial sites between the layers of the film, not just water molecules filling voids and defect sites alone. An increase in the film capacitance is observed, although the polymer chains retain all trans configuration of the ferroelectric phase. © 2004 American Institute of Physics.

Hypothetical Thermodynamic Properties: The Boiling And Critical Temperatures Of Polyethylene And Polytetrafluoroethylene, James S. Chickos

James Chickos

No abstract provided.

Extrinsic Control Of The Exchange Bias, Christian Binek

Christian Binek Publications

A new control mechanism for the exchange bias effect in magnetic heterostructures is proposed. It takes advantage of the magnetoelectric effect which takes place in the antiferromagnetic pinning layer. In contrast with the pioneering AC measurements of the magnetoelectric effect, we investigate the magnetic response of the prototypical magnetoelectric compound Cr2O3 on static electric fields. The linear dependence of the magnetic moment on the applied axial electric field and the temperature dependence of the corresponding slopes αshort parallel are measured by DC SQUID magnetometry. The contribution of the field-induced surface magnetization and its impact on the exchange bias effect is …

Study Of The Excited-State Absorption Properties Of Polymethine Molecules, Richard Stanley Lepkowicz

Electronic Theses and Dissertations

This dissertation investigates excited-state nonlinearities in a series of polymethine dyes for the application of nanosecond optical limiting. Optical limiters are devices that for low intensity light exhibit a high linear transmittance, but for high intensity light strongly attenuate the incident radiation. These devices would serve to protect optical sensors from intense laser radiation by clamping the maximum energy allowed through an optical system below the damage threshold of the sensor. The search is ongoing for optical materials that are both broadband and have high damage thresholds to be effective materials for limiting applications. Polymethine dyes are promising compounds due …

Control Of Trapped-Ion Quantum States With Optical Pulses, Chitra Rangan, A.M. Bloch, C. Monroe, P.H. Bucksbaum

Physics Publications

The control-theoretical analysis of control of trapped-ion quantum states is described with optical pulses in large Hilbert spaces. The resonant bichromatic fields were applied to completely uncontrollable and controllable systems. The specific temporal shapes of control fields are important to determine controllability of trapped system. The Hilbert space of qubit-harmonic oscillator is made finite and Schrödinger equation controllable through resonant bichromatic fields.

Broadband Precision Wavelength Meter Based On A Stepping Fabry-Pérot Interferometer, T.J. Scholl, Steven J. Rehse, R.A. Holt, S.D. Rosner

Physics Publications

We have constructed a broadband apparatus for wavelength metrology capable of absolute accuracy at a level of better than 2 parts in 109. An evacuated plane-parallel Fabry-Pérot interferometer with continuously adjustable mirror separation is used to compare the wavelength of a single-frequency tunable laser with that of an iodine-stabilized HeNe laser used as a wavelength standard. This work details apparatus construction, a thorough investigation of systematic errors, and data analysis. The wavelengths of five Doppler-free 130Te2 transitions in the region from 475.6 to 490.8 nm have been measured and are found to be in excellent agreement with previous measurements. In …

High Precision Variational Calculations For H2 +, M. M. Cassar, Gordon W. F. Drake

Physics Publications

A double basis set in Hylleraas coordinates is used to obtain improved variational upper bounds for the nonrelativistic energy of the 1 1S (v = 0, R = 0), 2 1S (v = 1, R = 0) and 2 3P (v = 0, R = 1) states of H2 +. This method shows a remarkable convergence rate for relatively compact basis set expansions. A comparison with the most recent work is made. The accuracy of the wavefunctions is tested using the electron-proton Kato cusp condition.

Hole Drift-Mobility Measurements And Multiple-Trapping In Microcrystalline Silicon, T. Dylla, F. Finger, Eric A. Schiff

Physics - All Scholarship

We present photocarrier time-of-flight measurements of the hole drift-mobility in microcrystalline silicon samples with a high crystalline volume fraction; typical roomtemperature values are about 1 cm2/Vs. Temperature-dependent measurements are consistent with the model of multiple-trapping in an exponential bandtail. While this model has often been applied to amorphous silicon, its success for predominantly crystalline samples is unexpected. The valence bandtail width is 31 meV, which is about 10-20 meV smaller than values reported for a-Si:H, and presumably reflects the greater order in the microcrystalline material. The hole band-mobility is about 1 cm2/Vs – essentially the same magnitude as has been …

Drift-Mobility Measurements And Mobility Edges In Disordered Silicons, Eric A. Schiff

Physics - All Scholarship

Published electron and hole drift-mobility measurements in hydrogenated amorphous silicon (a-Si:H), amorphous silicon alloys (a-SiGe:H and a-SiC:H), and microcrystalline silicon (μc-Si:H) are analysed in terms of the exponential bandtail trapping model. A three-parameter model was employed using an exponential bandtail width E, the band mobility μ0, and the attempt-toescape frequency ν. Low-temperature measurements indicate a value around μ0 = 1 cm2 V−1 s−1 for both the conduction and valence bands over the entire range of materials. High temperature-measurements for electrons in a-Si:H suggest a larger value of 7 cm2 V−1 s−1. These properties and those of the frequency ν are …