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Polarization

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Articles 91 - 120 of 122

Full-Text Articles in Physics

Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au + Au Collisions At Square Root Of Snn = 200 Gev And Constraints On Medium Transport Coefficients, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt Dec 2008

Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au + Au Collisions At Square Root Of Snn = 200 Gev And Constraints On Medium Transport Coefficients, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt

Aerospace, Physics, and Space Science Faculty Publications

For Au þ Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, pT, up to 20 GeV=c. A fivefold suppression is found, which is essentially constant for 5 < pT < 20 GeV=c. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e.g., hq^i in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au þ Au collisions.

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Long-Time Electron Spin Storage Via Dynamical Suppression Of Hyperfine-Induced Decoherence In A Quantum Dot, Wenxian Zhang, N. P. Konstantinidis, V. V. Dobrovitski, B. N. Harmon, Lea F. Santos, Lorenza Viola Mar 2008

Long-Time Electron Spin Storage Via Dynamical Suppression Of Hyperfine-Induced Decoherence In A Quantum Dot, Wenxian Zhang, N. P. Konstantinidis, V. V. Dobrovitski, B. N. Harmon, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

The coherence time of an electron spin decohered by the nuclear spin environment in a quantum dot can be substantially increased by subjecting the electron to suitable dynamical decoupling sequences. We analyze the performance of high-level decoupling protocols by using a combination of analytical and exact numerical methods, and by paying special attention to the regimes of large interpulse delays and long-time dynamics, which are outside the reach of standard average Hamiltonian theory descriptions. We demonstrate that dynamical decoupling can remain efficient far beyond its formal domain of applicability, and find that a protocol exploiting concatenated design provides best performance …

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Fast Domain Wall Motion In Nanostripes With Out-Of-Plane Fields, Andrew Kunz, Sarah C. Reiff Jan 2008

Fast Domain Wall Motion In Nanostripes With Out-Of-Plane Fields, Andrew Kunz, Sarah C. Reiff

Physics Faculty Research and Publications

Controlling domain wall motion is important due to the impact on the viability of proposed nanowire devices. One hurdle is slow domain wall speed when driven by fields greater than the Walker field due to nucleation of vortices in the wall. We present simulation results detailing the dynamics of these vortices including the nucleation and subsequent fast ejection of the vortex core leading to fast domain wall speeds. The ejection is due to the reversal of the core moments by an out-of-plane field. The technique can be used to produce domain walls of known orientation, independent of the initial state.

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Optical Absorption, Depolarization, And Scatter Of Epitaxial Single-Crystal Chemical-Vapor-Deposited Diamond At 1.064 Μm, Giorgio Turri, Ying Chen, Michael Bass Jun 2007

Optical Absorption, Depolarization, And Scatter Of Epitaxial Single-Crystal Chemical-Vapor-Deposited Diamond At 1.064 Μm, Giorgio Turri, Ying Chen, Michael Bass

Publications

No abstract provided.

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Gemini Mid-Ir Polarimetry Of Ngc 1068: Polarized Structures Around The Nucleus, C. Packham, S. Young, S. Fisher, K. Volk, R. Mason, J. H. Hough, P. F. Roche, Moshe Elitzur, J. Radomski, E. Perlman May 2007

Gemini Mid-Ir Polarimetry Of Ngc 1068: Polarized Structures Around The Nucleus, C. Packham, S. Young, S. Fisher, K. Volk, R. Mason, J. H. Hough, P. F. Roche, Moshe Elitzur, J. Radomski, E. Perlman

Physics and Astronomy Faculty Publications

We present diffraction-limited, 10 μm imaging polarimetry data for the central regions of the archetypal Seyfert active galactic nucleus NGC 1068. The position angle of polarization is consistent with three dominant polarizing mechanisms. We identify three distinct regions of polarization: (1) north of the nucleus, arising from aligned dust in the narrow emission line region, (2) south, east, and west of the nucleus, consistent with dust being channeled toward the central engine, and (3) a central minimum of polarization consistent with a compact (≤22 pc) torus. These observations provide continuity between the geometrically and optically thick torus and the …

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Electric Field Induced Hopping Conductivity And Polarization In Hytrel, Steve Hart Apr 2007

Electric Field Induced Hopping Conductivity And Polarization In Hytrel, Steve Hart

Senior Theses and Projects

The focus of my 4900 research project is centered on the conductivity of Hytrel, a complex, newly developed block co-polymer. I first began to study Hytrel during the summer of 2006, as part of the USU College of Science Mini-Grant program1. My general objective was to study the relationship between the resistivity of Hytrel and hopping conductivity. Hopping conductivity is a theory of electron transport for nonconducting solids, originally developed for amorphous semiconductors2,3. The theory will be examined in greater detail later in this document. While studying this relationship last summer, I noticed an unusual phenomenon …

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Schroedinger Representation For The Polarized Gowdy Model, Charles G. Torre Jan 2007

Schroedinger Representation For The Polarized Gowdy Model, Charles G. Torre

All Physics Faculty Publications

The polarized T3 Gowdy model is, in a standard gauge, characterized by a point particle degree of freedom and a scalar field degree of freedom obeying a linear field equation on R × S1. The Fock representation of the scalar field has been well studied. We construct the Schrödinger representation for the scalar field at a fixed value of the Gowdy time in terms of square-integrable functions on a space of distributional fields with a Gaussian probability measure. We show that 'typical' field configurations are slightly more singular than square-integrable functions on the circle. For each time the corresponding Schrödinger …

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Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem Jan 2007

Effects Of Polarization And Coherence On The Propagation And The Detection Of Stochastic Electromagnetic Beams, Mohamed Fouad Salem

Electronic Theses and Dissertations

Most of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the properties of any stochastic field such as the spectral density and the spectral degree of coherence on propagation in any linear medium, deterministic …

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First Measurement Of Beam-Recoil Observables CX And CZ In Hyperon Photoproduction, M. J. Amaryan, H. Bagdasaryan, H. Bektasoglu, S. Bültmann, S. L. Careccia, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, S. E. Kuhn, J. Lachniet, M. R. Niroula, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration Jan 2007

First Measurement Of Beam-Recoil Observables CX And CZ In Hyperon Photoproduction, M. J. Amaryan, H. Bagdasaryan, H. Bektasoglu, S. Bültmann, S. L. Careccia, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, S. E. Kuhn, J. Lachniet, M. R. Niroula, R. A. Niyazov, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

Spin transfer from circularly polarized real photons to recoiling hyperons has been measured for the reactions →γ + p → K+ + →Λ and →γ+p → K+ + →Σ0. The data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS) detector at the Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85 < cos θc.m.K+ < +0.95. For the Λ, the polarization transfer coefficient along the photon momentum axis, Cz, was found to be near unity for a wide range of energy and kaon production angles. The associated transverse polarization coefficient Cx is smaller than Cz by a roughly …

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Methods For Resistivity Measurements Related To Spacecraft Charging, John R. Dennison, Jerilyn Brunson, Prasanna Swaminathan, Nelson Green, A. Robb Frederickson Oct 2006

Methods For Resistivity Measurements Related To Spacecraft Charging, John R. Dennison, Jerilyn Brunson, Prasanna Swaminathan, Nelson Green, A. Robb Frederickson

All Physics Faculty Publications

A key parameter in modeling differential spacecraft-charging is the resistivity of insulating materials. This parameter determines how charge will accumulate and redistribute across the spacecraft, as well as the timescale for charge transport and dissipation. American Society for Testing and Materials constant-voltage methods are shown to provide inaccurate resistivity measurements for materials with resistivities greater than ~1017 Omegamiddotcm or with long polarization decay times such as are found in many polymers. These data have been shown to often be inappropriate for spacecraft-charging applications and have been found to underestimate charging effects by one to four orders of magnitude for …

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Experimentally Derived Resistivity For Dielectric Samples From The Crres Internal Discharge Monitor, Nelson W. Green, A. Robb Frederickson, John R. Dennison Oct 2006

Experimentally Derived Resistivity For Dielectric Samples From The Crres Internal Discharge Monitor, Nelson W. Green, A. Robb Frederickson, John R. Dennison

All Physics Faculty Publications

Resistivity values were experimentally determined using charge-storage methods for six samples remaining from the construction of the internal discharge monitor flown on the Combined Release and Radiation Effects Satellite (CRRES). Three tests were performed over a period of three to five weeks each in a vacuum of ~5times10-6 torr with an average temperature of ~25degC to simulate a space environment. Samples tested included FR4, polytetrafluoroethylene (PTFE), and alumina with copper electrodes attached to one or more of the sample surfaces. FR4 circuit-board material was found to have a dark-current resistivity of ~1times1018 Omegamiddotcm and a moderately high polarization …

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Quantum Electrodynamic Corrections To The Hyperfine Structure Of Excited S States, Ulrich D. Jentschura, Vladimir A. Yerokhin Jun 2006

Quantum Electrodynamic Corrections To The Hyperfine Structure Of Excited S States, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

State-dependent quantum electrodynamic corrections are evaluated for the hyperfine splitting of nS states for arbitrary principal quantum number n. The calculations comprise both the self-energy and the vacuum-polarization correction of order α(Zα) 2 EF and the recoil correction of order (Zα)2 (m/M) EF. Higher-order corrections are summarized and partly reevaluated as well. Accurate predictions for hydrogen hyperfine splitting intervals of nS states with n=2,...,8 are presented. The results obtained are important due to steady progress in hydrogen spectroscopy for transitions involving highly excited S states.

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Probing Random Media With Singular Waves, Chaim Schwartz Jan 2006

Probing Random Media With Singular Waves, Chaim Schwartz

Electronic Theses and Dissertations

In recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular momentum transfer. Angular momentum carried by light can be, in many cases, divided in two terms. The first one relates to the polarization of light and …

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Differential Cross Sections For 𝛾 + P → K⁺ + Y For Λ And Σ⁰ Hyperons, H. Bagdasaryan, M. Bektasoglu, S. L. Careccia, S. Bültmann, G. E. Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. V. Klimenko, S. E. Kuhn, S. Tkachenko, L. B. Weinstein, J. Zhang, Et Al., Clas Collaboration Jan 2006

Differential Cross Sections For 𝛾 + P → K⁺ + Y For Λ And Σ⁰ Hyperons, H. Bagdasaryan, M. Bektasoglu, S. L. Careccia, S. Bültmann, G. E. Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. V. Klimenko, S. E. Kuhn, S. Tkachenko, L. B. Weinstein, J. Zhang, Et Al., Clas Collaboration

Physics Faculty Publications

High-statistics cross sections for the reactions 𝛾 + p → K⁺ + Λ and 𝛾 + p → K⁺ + Σ⁰ have been measured using CLAS at Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85 < cos θ Kc.m. < +0.95. In the K⁺ + Λ channel we confirm a resonance-like structure near W=1.9 GeV at backward kaon angles. The position and width of this structure change with angle, indicating that more than one resonance is likely playing a role. The K⁺ + Λ channel at forward angles and all energies is well described by a t-channel scaling characteristic of Regge exchange, whereas the same scaling applied to the K⁺ + Σ⁰ channel is less successful. Several existing theoretical models are compared to the data, but none provide a good representation of the results.

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Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel Nov 2005

Laser-Dressed Vacuum Polarization In A Coulomb Field, A. I. Milstein, Ivan S. Terekhov, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

We investigate quantum electrodynamic effects under the influence of an external, time-dependent electromagnetic field, which mediates dynamic modifications of the radiative corrections. Specifically, we consider the quantum electrodynamic vacuum-polarization tensor under the influence of two external background fields: a strong laser field and a nuclear Coulomb field. We calculate the charge and current densities induced by a nuclear Coulomb field in the presence of a laser field. We find the corresponding induced scalar and vector potentials. The induced potential, in first-order perturbation theory, leads to a correction to atomic energy levels. The external laser field breaks the rotational symmetry of …

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Cosmic Shear Of The Microwave Background: The Curl Diagnostic, Asantha Cooray, Marc Kamionkowski, Robert R. Caldwell Jun 2005

Cosmic Shear Of The Microwave Background: The Curl Diagnostic, Asantha Cooray, Marc Kamionkowski, Robert R. Caldwell

Dartmouth Scholarship

Weak-lensing distortions of the cosmic-microwave-background (CMB) temperature and polarization patterns can reveal important clues to the intervening large-scale structure. The effect of lensing is to deflect the primary temperature and polarization signal to slightly different locations on the sky. Deflections due to density fluctuations, gradient-type for the gradient of the projected gravitational potential, give a direct measure of the mass distribution. Curl-type deflections can be induced by, for example, a primordial background of gravitational waves from inflation or by second-order effects related to lensing by density perturbations. Whereas gradient-type deflections are expected to dominate, we show that curl-type deflections can …

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Modelling Continuum Optical And Ultraviolet Polarization Of Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell Jun 2005

Modelling Continuum Optical And Ultraviolet Polarization Of Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell

Department of Physics and Astronomy: Faculty Publications

We present results from a new Monte Carlo radiative transfer computer code, STOKES, developed to model polarization induced by scattering off free electrons and dust grains. STOKES is freely available on the web and can be used to model scattering in a wide variety of astrophysical situations. For edge-on (type-2) viewing positions, the polarization produced by a dusty torus alone is largely wavelength-independent.

This is because the torus is optically thick and the change in albedo with wavelength is slight. Wavelength-independent polarization therefore does not necessarily imply electron scattering. We are able to fully explain wavelength independent type-2 polarization without …

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Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin Mar 2005

Positronium Formation In Positron-Li And Positron-Na Collisions At Low Energies, Anh-Thu Le, M. W. J. Bromley, C. D. Lin

Physics Faculty Research & Creative Works

We present the positronium formation cross sections for a positron colliding with lithium and sodium for the collision energies from 0.01 eV up to 20 eV by the hyperspherical close-coupling method. For Li, our results agree with the experimental data and with other calculations. Our results for Na remain in agreement with previous close-coupling calculations, but do not support the latest experimental data for Na below 1 eV. To validate our model potentials and method in the low-energy regime, the binding energies of positronic lithium and positronic sodium as well as the s-wave scattering lengths for positronium scattering from Li⁺ …

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Beam-Helicity Asymmetries In Double-Charged-Pion Photoproduction On The Proton, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, Gail Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, S. E. Kuhn, L. M. Qin, W. Roberts, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, J. Zhang, Et Al., Clas Collaboration Jan 2005

Beam-Helicity Asymmetries In Double-Charged-Pion Photoproduction On The Proton, H. Bagdasaryan, M. Bektasoglu, S. Bültmann, Gail Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. Klein, S. E. Kuhn, L. M. Qin, W. Roberts, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, J. Zhang, Et Al., Clas Collaboration

Physics Faculty Publications

Beam-helicity asymmetries for the two-pion-photoproduction reaction 𝛾⃗p → p π+π- have been studied for the first time in the resonance region for center-of-mass energies between 1.35 and 2.30 GeV. The experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer using circularly polarized tagged photons incident on an unpolarized hydrogen target. Beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics and dynamics of the reaction. The data are compared with the results of various phenomenological model calculations, and show that these models currently do not …

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Nonlinear Optics And An Experimental Test Of Bell’S Inequality, Michael Herbst Jan 2005

Nonlinear Optics And An Experimental Test Of Bell’S Inequality, Michael Herbst

Honors Papers

The purpose of this investigation is to assemble an apparatus capable of testing Bell’s inequality for a local hidden variable. The historical context and theoretical developments that led to this area of inquiry are presented. Expected experimental results stemming from two distinct physical theories are introduced. Procedures are given that outline the assembly of a device capable of testing these theories. Analysis confirming the successful completion of a majority of the steps is presented, and the final necessary steps are detailed. Finally, a laboratory prompt for this experiment’s use in Oberlin College’s advanced laboratory class is given.

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Nonrelativistic Qed Approach To The Bound-Electron G Factor, Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin Oct 2004

Nonrelativistic Qed Approach To The Bound-Electron G Factor, Krzysztof Pachucki, Ulrich D. Jentschura, Vladimir A. Yerokhin

Physics Faculty Research & Creative Works

Within a systematic approach based on nonrelativistic quantum electrodynamics, we derive the one-loop self-energy correction of order α ( Z α )4 to the bound-electron g factor. In combination with numerical data, this analytic result improves theoretical predictions for the self-energy correction for carbon and oxygen by an order of magnitude. Basing on one-loop calculations, we obtain the logarithmic two-loop contribution of order α2 ( Z α )4 ln [ ( Z α )- 2 ] and the dominant part of the corresponding constant term. The results obtained improve the accuracy of the theoretical predictions for …

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Gold Adatoms And Dimers On Relaxed Graphite Surfaces, Guan Ming Wang, Joseph J. Belbruno, Steven D. Kenny, Roger Smith May 2004

Gold Adatoms And Dimers On Relaxed Graphite Surfaces, Guan Ming Wang, Joseph J. Belbruno, Steven D. Kenny, Roger Smith

Dartmouth Scholarship

The interaction of deposited gold adatoms and dimers with multilayer relaxed graphite surfaces is investigated through a density functional approach with numerical orbitals and a relativistic core pseudopotential. The energy landscape for a gold adatom along [110] agrees with scanning tunneling microscopy observations including the preferred β binding site for adatoms and the mobility difference between silver and gold adatoms. Deposited particles are shown to induce surface deformation and polarization. Static relaxation and dynamic simulations indicate that the energetically preferred binding orientation for a gold dimer is normal rather than parallel to the graphite surface. The dimer response to a …

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Microsecond Spin-Flip Times In N-Gaas Measured By Time-Resolved Polarization Of Photoluminescence, John S. Colton, T. A. Kennedy, A. S. Bracker, D. Gammon Mar 2004

Microsecond Spin-Flip Times In N-Gaas Measured By Time-Resolved Polarization Of Photoluminescence, John S. Colton, T. A. Kennedy, A. S. Bracker, D. Gammon

Faculty Publications

We have observed microsecond spin-flip times in lightly doped n-GaAs, by measuring the photoluminescence polarization in the time domain with pump and probe pulses. Times up to 1.4 μs have been measured. Our results as a function of magnetic field indicated three regions governing the spin relaxation: a low field region, where spin-flip times increase due to suppression of the nuclear hyperfine interaction for localized electrons, a medium field region where spin-flip times increase due to narrowing of the hyperfine relaxation for interacting electrons, and a high field region where spin-flip times begin to level off due to the increasing …

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A Test Of Bell’S Inequality For The Undergraduate Laboratory, Burton A. Betchart Jan 2004

A Test Of Bell’S Inequality For The Undergraduate Laboratory, Burton A. Betchart

Honors Papers

The thesis documents the work done over the year to initiate an undergraduate Advanced Laboratory experiment which tests Bell’s inequality. It provides reference theory for the experiment, including explanations of Bell inequalities, basics of nonlinear optics, type-I downconversion and entanglement, and polarization states of the entangled photons. A main result is the equipment and design proposal for the experiment, which will cost a total $19600, led in price by the $9000 of a four photodetector array and followed by the $5000 of a 405nm pump laser. Entangled photons are produced by pumping BBO in a two-crystal geometry. Although most of …

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Complete Angular Distribution Measurements Of Two-Body Deuteron Photodisintegration Between 0.5 And 3 Gev, H. Bagdasaryan, H. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, A. Klein, A. V. Klimenko, S. E. Kuhn, F. Sabatié, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration Jan 2004

Complete Angular Distribution Measurements Of Two-Body Deuteron Photodisintegration Between 0.5 And 3 Gev, H. Bagdasaryan, H. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, A. Klein, A. V. Klimenko, S. E. Kuhn, F. Sabatié, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration

Physics Faculty Publications

Nearly complete angular distributions of the two-body deuteron photodisintegration differential cross section have been measured using the CEBAF Large Acceptance Spectrometer detector and the tagged photon beam at the Thomas Jefferson National Accelerator Facility. The data cover photon energies between 0.5 and 3.0 GeV and center-of-mass proton scattering angles 10°–160°. The data show a persistent forward-backward angle asymmetry over the explored energy range, and are well described by the nonperturbative quark gluon string model.

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Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala Jan 2004

Influence Of Antenna Aiming On Ece In Mast, Josef Preinhaelter, Jakub Urban, Pavol Pavlo, Vladimir Shevchenko, Martin Valovič, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The effect of the direction of the detected beam on the intensity of ECE is studied. It is found that the combined effects of the strong dependence of the conversion efficiencey of O mode at the plasma resonance on the direction of the incident wave and the partial screening of the beam waist by the MAST vessel wall, can be responsible for the weakening of ECE emission for some frequencies. The theoretical model for ECE data interpretation on MAST has been significantly improved. New features of the model are as follows: the quasioptical treatment of the receiving antenna, interference, polarization …

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Superfluorescence Polarization: Signature Of Collisional Redistribution, A. Kumarakrishnan, S. Chudasama, Xianming Han Jan 2003

Superfluorescence Polarization: Signature Of Collisional Redistribution, A. Kumarakrishnan, S. Chudasama, Xianming Han

Scholarship and Professional Work - LAS

We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p1P1–3d4s1D2 transition at 5.5μm. These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s21S0–4s4p1P1 transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through 90° for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1 state can be estimated using a simple model …

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Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich Jul 2001

Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25PW/cm2 laser pulses at 795 nm have been measured using a “reaction microscope.” At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical “recollision model” revealed an (e,2e)-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield.

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Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky Jan 2000

Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky

Physics Faculty Publications

There are two possible sources of the factorial large-order behavior of a typical perturbative series. First, the number of different Feynman diagrams may be large; second, there may be abnormally large diagrams known as renormalons. It is well known that the large combinatorial number of diagrams is described by instanton-type solutions of the classical equations. We demonstrate that, from the functional-integral viewpoint, the renormalons do not correspond to a particular configuration but manifest themselves as dilatation modes in the functional space.

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Polarization Of Astronomical Maser Radiation. Iv. Circular Polarization Profiles, Moshe Elitzur Sep 1998

Polarization Of Astronomical Maser Radiation. Iv. Circular Polarization Profiles, Moshe Elitzur

Physics and Astronomy Faculty Publications

Profile comparison of the Stokes parameters V and I is a powerful tool for maser data analysis, which provides the first direct methods for unambiguous determination of (1) the maser saturation stage, (2) the amplification optical depth and intrinsic Doppler width of unsaturated masers, and (3) the comparative magnitudes of Zeeman splitting and Doppler line width. Circular polarization recently detected in OH 1720 MHz emission from the Galactic center appears to provide the first direct evidence for maser saturation.

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