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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Efficient reflection via four-wave mixing in a Doppler-free electromagnetically-induced-transparency gas system

We experimentally demonstrate the high-efficiency reflection of a probe field in {Lambda}-type three-level atoms of cesium vapor driven by two counterpropagating coupling fields. More than 60% of reflection efficiency is observed at the phase-matching angle. The underlying mechanism theoretically is investigated as the four-wave mixing is enhanced by the electromagnetically-induced transparency. Both of the two Doppler-free two-photon resonances (one for the probe and co-propagating fields, the other for the reflected and the counterpropagation fields) play an important role in satisfying the phase matching in the reflection direction. The phase compensation due to the anomalous dispersion and the decrease of effective absorption length in the atomic system allow the efficient reflection to be observed in a wide range of incident angles of the probe field and detunings of the coupling field.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Finite-temperature electromagnetic-field quantization in a medium: The thermofield approach

Starting from a Lagrangian, an electromagnetic field is quantized in the presence of a medium in thermal equilibrium and also in a medium with time-varying temperature. The vector potential for both equilibrium and nonequilibrium cases is obtained and vacuum fluctuations of the fields are calculated. As an illustrative example, the finite-temperature decay rate and level shift of an atom in a polarizable medium are calculated in this approach.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Discontinuities in the electromagnetic fields of vortex beams in the complex source-sink model

An analytical discontinuity is reported in what was thought to be the discontinuity-free exact nonparaxial vortex beam phasor obtained within the complex source-sink model. This discontinuity appears for all odd values of the orbital angular momentum mode. Such discontinuities in the phasor lead to nonphysical discontinuities in the real electromagnetic field components. We identify the source of the discontinuities, and provide graphical evidence of the discontinuous real electric fields for the first and third orbital angular momentum modes. Additionally, a simple means of avoiding these discontinuities is presented.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Parity-time electromagnetic diodes in a two-dimensional nonreciprocal photonic crystal

We propose a kind of electromagnetic (EM) diode based on a two-dimensional nonreciprocal gyrotropic photonic crystal. This periodic microstructure has separately broken symmetries in both parity (P) and time-reversal (T) but obeys parity-time (PT) symmetry. This kind of diode could support bulk one-way propagating modes either for group velocity or phase velocity with various types of negative and positive refraction. This symmetry-broken system could be a platform to realize abnormal photoelectronic devices, and it may be analogous to an electron counterpart with one-way features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Electromagnetic decays of excited states in {sup 261}Sg (Z=106) and {sup 257}Rf (Z=104)

An isomeric one-quasineutron state, likely based on the [725]11/2{sup -} Nilsson level, was identified in {sup 261}Sg by its decay via internal conversion electrons. The state has an excitation energy of approx =200 keV and a half-life of 9.0{sub -1.5}{sup +2.0} mus. {sup 261}Sg has the highest Z and A of any nucleus in which the electromagnetic decay of an isomeric state was observed to date. A separate experiment was performed on the alpha daughter nucleus of {sup 261}Sg, namely {sup 257}Rf. Spectroscopy of delayed gamma rays and converted electrons from {sup 257}Rf resulted in the identification of a K isomer at an excitation energy of approx =1125 keV with a half-life of 134.9 +- 7.7 mus. The spin of the isomeric state is tentatively assigned I=21/2,23/2 and the state likely decays to a rotational band built on the [725]11/2{sup -} Nilsson level via a DELTAK=5 or 6 transition. The present results provide new information on excited states in the transactinide region, which is important for testing models of the heaviest elements.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Electromagnetic form factors of nucleons in the extended vector meson dominance model

The extended vector meson dominance model, which allows one to describe the electromagnetic form factors of nucleons obeying the asymptotic quark counting rule prescriptions and contains the minimal number of free parameters, is presented. We obtain a reasonable fit of form factors over the experimentally available spacelike region of momentum transfer and reasonable results in the timelike region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Symmetries of higher-spin fields and the electromagnetic N{yields}N{sup *}(1680) form factors

We study the Q{sup 2} evolution of the form factors (FFs) for the nucleon-to-N*(1680) transition in the framework of effective field theory. To this end, the intrinsic symmetries of the spin-(5/2) Rarita-Schwinger (RS) fields are analyzed, and a Lagrangian of the electromagnetic NN*(1680) interactions is constructed. The Lagrangian preserves all the intrinsic symmetries of the spin-(5/2) field--point and gauge invariance--and does not involve lower-spin components of the reducible RS field. In addition, the symmetries postulate the definitions of the Lagrangian FFs. These FFs are modeled as dispersionlike expansions in a vector-meson-dominance model. A good agreement with the experimental data is achieved.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Role of mesons in the electromagnetic form factors of the nucleon

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q{sup 2} behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q{sup 2} or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as ''charge distributions,'' nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment-theory comparisons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Rigorous pion electromagnetic form factor behavior in the spacelike region

Precise experimental information on {sigma}{sub tot}(e{sup +}e{sup -}{yields}{pi}{sup +}{pi}{sup -}) is transferred into the spacelike region by taking advantage of the analyticity. As a result, rigorous pion electromagnetic form factor behavior in spacelike region is obtained. The latter is compared with some existing model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Nucleon electromagnetic form factors and electroexcitation of low lying nucleon resonances in a light-front relativistic quark model

We utilize a light-front relativistic quark model (LF RQM) to predict the 3q core contribution to the electroexcitation amplitudes for the {Delta}(1232)P{sub 33}, N(1440)P{sub 11}, N(1520)D{sub 13}, and N(1535)S{sub 11} up to Q{sup 2} = 12 GeV{sup 2}. The parameters of the model have been specified via description of the nucleon electromagnetic form factors in the approach that combines 3q and pion-cloud contributions in the LF dynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Cerenkov radio pulses from electromagnetic showers in the time domain

The electric field of the Cerenkov radio pulse produced by a single charged particle track in a dielectric medium is derived from first principles. An algorithm is developed to obtain the pulse in the time domain for numerical calculations. The algorithm is implemented in a Monte Carlo simulation of electromagnetic showers in dense media (specifically designed for coherent radio emission applications) as might be induced by interactions of ultrahigh energy neutrinos. The coherent Cerenkov radio emission produced by such showers is obtained simultaneously both in the time and frequency domains. A consistency check performed by Fourier transforming the pulse in time and comparing it to the frequency spectrum obtained directly in the simulations yields, as expected, fully consistent results. The reversal of the time structure inside the Cerenkov cone and the signs of the corresponding pulses are addressed in detail. The results, besides testing algorithms used for reference calculations in the frequency domain, shed new light into the properties of the radio pulse in the time domain. The shape of the pulse in the time domain is directly related to the depth development of the excess charge in the shower and its width to the observation angle with respect to the Cerenkov direction. This information can be of great practical importance for interpreting actual data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Electromagnetic form factors of the {Omega}{sup -} in lattice QCD

We present results on the omega baryon ({Omega}{sup -}) electromagnetic form factors using N{sub f}=2+1 domain-wall fermion configurations for three pion masses in the range of about 350 to 300 MeV. We compare results obtained using domain-wall fermions with those of a mixed-action (hybrid) approach, which combines domain-wall valence quarks on staggered sea quarks, for a pion mass of about 350 MeV. We pay particular attention in the evaluation of the subdominant electric quadrupole form factor to sufficient accuracy to exclude a zero value, by constructing a sequential source that isolates it from the dominant form factors. The {Omega}{sup -} magnetic moment, {mu}{sub {Omega}}{sup -}, and the electric charge and magnetic radius, <r{sub E0/M1}{sup 2}>, are extracted for these pion masses. The electric quadrupole moment is determined for the first time using dynamical quarks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Neutrino pair emission off electrons in a strong electromagnetic wave field

The emission of {nu}{nu} pairs off electrons in a polarized ultraintense electromagnetic (e.g., laser) wave field is analyzed. We elaborate on the significance of nonlinear electrodynamics effects (i.e., multiphoton processes) and the peculiarities of neutrino production. Special attention is devoted to the convergence of the reaction probabilities as a function of the number of absorbed photons. Expressions for large field intensities are provided. The asymmetry between the probabilities of electron and {mu}+{tau} neutrino production depends on initial conditions such as energy of the wave field photons and the field intensity. These findings differ from the lowest-order perturbative calculation of the reaction {gamma}+e{yields}e{sup '}+{nu}{nu}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nonminimally coupled gravitational and electromagnetic fields: pp-wave solutions

We give the Lagrangian formulation of a generic nonminimally extended Einstein-Maxwell theory with an action that is linear in the curvature and quadratic in the electromagnetic field. We derive the coupled field equations by a first-order variational principle using the method of Lagrange multipliers. We look for solutions describing plane-fronted Einstein-Maxwell waves with parallel rays. We give a family of exact pp-wave solutions associated with a partially massless spin-2 photon and a partially massive spin-2 graviton.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nucleon electromagnetic form factors in twisted mass lattice QCD

We present results on the nucleon electromagnetic form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1 fm and L=2.8 fm. Cutoff effects are investigated using three different values of the lattice spacings, namely a=0.089 fm, a=0.070 fm and a=0.056 fm. The nucleon magnetic moment, Dirac and Pauli radii are obtained in the continuum limit and chirally extrapolated to the physical pion mass allowing for a comparison with experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Implications of the recent high statistics determination of the pion electromagnetic form factor in the timelike region

The recently evaluated two-pion contribution to the muon g-2 and the phase of the pion electromagnetic form factor in the elastic region, known from {pi}{pi} scattering by Fermi-Watson theorem, are exploited by analytic techniques for finding correlations between the coefficients of the Taylor expansion at t=0 and the values of the form factor at several points in the spacelike region. We do not use specific parametrizations, and the results are fully independent of the unknown phase in the inelastic region. Using for instance, from recent determinations, <r{sub {pi}}{sup 2}>=(0.435{+-}0.005) fm{sup 2} and F(-1.6 GeV{sup 2})=0.243{sub -0.014}{sup +0.022}, we obtain the allowed ranges 3.75 GeV{sup -4} < or approx. c < or approx. 3.98 GeV{sup -4} and 9.91 GeV{sup -6} < or approx. d < or approx. 10.46 GeV{sup -6} for the curvature and the next Taylor coefficient, with a strong correlation between them. We also predict a large region in the complex plane where the form factor cannot have zeros.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Electromagnetic Casimir piston in higher-dimensional spacetimes

We consider the Casimir effect of the electromagnetic field in a higher-dimensional spacetime of the form MxN, where M is the four-dimensional Minkowski spacetime and N is an n-dimensional compact manifold. The Casimir force acting on a planar piston that can move freely inside a closed cylinder is investigated. Different combinations of perfectly conducting boundary conditions and infinitely permeable boundary conditions are imposed on the cylinder and the piston. It is verified that if the piston and the cylinder have the same boundary conditions, the piston is always going to be pulled towards the closer end of the cylinder. However, if the piston and the cylinder have different boundary conditions, the piston is always going to be pushed to the middle of the cylinder. By taking the limit where one end of the cylinder tends to infinity, one obtains the Casimir force acting between two parallel plates inside an infinitely long cylinder. The asymptotic behavior of this Casimir force in the high temperature regime and the low temperature regime are investigated for the case where the cross section of the cylinder in M is large. It is found that if the separation between the plates is much smaller than the size of N, the leading term of the Casimir force is the same as the Casimir force on a pair of large parallel plates in the (4+n)-dimensional Minkowski spacetime. However, if the size of N is much smaller than the separation between the plates, the leading term of the Casimir force is 1+h/2 times the Casimir force on a pair of large parallel plates in the four-dimensional Minkowski spacetime, where h is the first Betti number of N. In the limit the manifold N vanishes, one does not obtain the Casimir force in the four-dimensional Minkowski spacetime if h is nonzero. Therefore the data obtained from Casimir experiments suggest that the first Betti number of the extra dimensions should be zero.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Electromagnetic surface modes in a magnetized quantum electron-hole plasma

The propagation of surface electromagnetic waves along a uniform magnetic field is studied in a quantum electron-hole semiconductor plasma. A forward propagating mode is found by including the effect of quantum tunneling. In the classical limit (({h_bar}/2{pi}){yields}0), one of the low-frequency modes found is similar to an experimentally observed one in n-type InSb at room temperature. The surface modes are shown to be significantly modified in the case of high-conductivity semiconductor plasmas where electrons and holes may be degenerate. The effects of the external magnetic field and the quantum tunneling on the surface wave modes are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗