Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ELECTROMAGNETS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Electromagnetic wave propagation based upon spectral-element methodology in dispersive and attenuating media

SUMMARY We build on mathematical equivalences between Maxwell’s wave equations for an electromagnetic medium and elastic seismic wave equations. This allows us to readily model Maxwell’s wave propagation in the spectral-element codes SPECFEM2D and SPECFEM3D, written for acoustic, viscoelastic and poroelastic seismic wave propagation, providing the ability to handle complex geometries, inherent to finite-element methods and retaining the strength of exponential convergence and accuracy due to the use of high-degree polynomials to interpolate field functions on the elements, characteristic to spectral-element methods (SEMs). Attenuation and dispersion processes related to the frequency dependence of dielectric permittivity and conductivity are also included using a Zener model, similar to shear attenuation in viscoelastic media or viscous diffusion in poroelastic media, and a Kelvin–Voigt model, respectively. Ability to account for anisotropic media is also discussed. Here, we limit ourselves to certain dielectric permittivity tensor geometries, in order to conserve a diagonal mass matrix after discretization of the system of equations. Doing so, simulation of Maxwell’s wave equations in the radar frequency range based on SEM can be solved using explicit time integration schemes well suited for parallel computation. We validate our formulation with analytical solutions. In 2-D, our implementation allows for the modelling of both a transverse magnetic (TM) mode, suitable for surface based reflection ground penetration radar type of applications, and a transverse electric (TE) mode more suitable for crosshole and vertical radar profiling setups. Two 2-D examples are designed to demonstrated the use of the TM and TE modes. A 3-D example is also presented, which allows for the full TEM solution, different antenna orientations, and out-of-plane variations in material properties.

58 GEOSCIENCES↗
DOE OSTI2018

Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers

The electromagnetic transients accompanying compact binary mergers (γ-ray bursts, afterglows and ‘macronovae’) are crucial to pinpoint the sky location of gravitational wave sources. Macronovae are caused by the radioactivity from freshly synthesized heavy elements, e.g. from dynamic ejecta and various types of winds. We study macronova signatures by using multidimensional radiative transfer calculations. We then employ the radiative transfer code SUPERNU and state-of-the-art LTE opacities for a few representative elements from the wind and dynamical ejecta (Cr, Pd, Se, Te, Br, Zr, Sm, Ce, Nd, U) to calculate synthetic light curves and spectra for a range of ejecta morphologies. The radioactive power of the resulting macronova is calculated with the detailed input of decay products. We assess the detection prospects for our most complex models, based on the portion of viewing angles that are sufficiently bright, at different cosmological redshifts (z). The brighter emission from the wind is unobscured by the lanthanides (or actinides) in some of the models, permitting non-zero detection probabilities for redshifts up to z = 0.07. We also find that the nuclear mass model and the resulting radioactive heating rate are crucial for the detectability. While for the most pessimistic heating rate (from the finite range droplet model) no reasonable increase in the ejecta mass or velocity, or wind mass or velocity, can possibly make the light curves agree with the observed near-infrared excess after GRB130603B, a more optimistic heating rate (from the Duflo–Zuker model) leads to good agreement. We conclude that future reliable macronova observations would constrain nuclear heating rates, and consequently help constrain nuclear mass models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Electromagnetically induced transparency in mechanical effects of light

We consider the dynamical behavior of a nanomechanical mirror in a high-quality cavity under the action of a coupling laser and a probe laser. We demonstrate the existence of the analog of electromagnetically induced transparency (EIT) in the output field at the probe frequency. Our calculations show explicitly the origin of EIT-like dips as well as the characteristic changes in dispersion from anomalous to normal in the range where EIT dips occur. Remarkably the pump-probe response for the optomechanical system shares all the features of the {Lambda} system as discovered by Harris and collaborators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Phase modulation induced by cooperative effects in electromagnetically induced transparency

We analyze the influence of dipole-dipole interactions in an electromagnetically induced transparency set up for a density at the onset of cooperative effects. To this end, we include mean-field models for the influence of local-field corrections and radiation trapping into our calculation. We show both analytically and numerically that the polarization contribution to the local field strongly modulates the phase of a weak pulse. We give an intuitive explanation for this local-field-induced phase modulation and demonstrate that it distinctively differs from the nonlinear self-phase-modulation that a strong pulse experiences in a Kerr medium.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Linear and nonlinear light propagations in a Doppler-broadened medium via electromagnetically induced transparency

We present a systematic theoretical study to deal with linear and nonlinear light propagations in a Doppler-broadened three-level {Lambda} system via electromagnetically induced transparency (EIT), with incoherent population exchange between two lower energy levels taken into account. Through a careful analysis of base state and linear excitation, we show that the EIT condition of the system is given by |{Omega}{sub c}|{sup 2{gamma}}{sub 31}>>2{gamma}{sub 21{Delta}{omega}D}{sup 2}, where {Omega}{sub c} is half the Rabi frequency of the control field, {Delta}{omega}{sub D} is the Doppler width, and {gamma}{sub jl} is the decay rate of the coherence between states |j> and |l>. Under this condition, the effect of incoherent population exchange is insignificant, while dephasing dominates the decoherence of the system. This condition also ensures the validity of the weak nonlinear perturbation theory used in this work for solving the Maxwell-Bloch equations with inhomogeneous broadening. We then investigate the nonlinear propagation of the probe field and show that it is possible to form temporal optical solitons in the Doppler-broadened medium. Such solitons have ultraslow propagating velocity and can be generated in very low light power. The possibility of realizing (1+1)-dimensional and (2+1)-dimensional spatial optical solitons in the adiabatic regime of the system is also discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Electromagnetic analysis of arbitrarily shaped pinched carpets

We derive the expressions for the anisotropic heterogeneous tensors of permittivity and permeability associated with two-dimensional and three-dimensional carpets of an arbitrary shape. In the former case, we map a segment onto smooth curves whereas in the latter case we map an arbitrary region of the plane onto smooth surfaces. Importantly, these carpets display no singularity of the permeability and permeability tensor components. Moreover, a reduced set of parameters leads to nonmagnetic two-dimensional carpets in p polarization (i.e., for a magnetic field orthogonal to the plane containing the carpet). Such an arbitrarily shaped carpet is shown to work over a finite bandwidth when it is approximated by a checkerboard with 190 homogeneous cells of piecewise constant anisotropic permittivity. We finally perform some finite element computations in the full vector three-dimensional case for a plane wave in normal incidence and a Gaussian beam in oblique incidence. The latter requires perfectly matched layers set in a rotated coordinate axis which exemplifies the role played by geometric transforms in computational electromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Engineering biphoton wave packets with an electromagnetically induced grating

We propose to shape biphoton wave packets with an electromagnetically induced grating in a four-level double-{Lambda} cold atomic system. We show that the induced hybrid grating plays an essential role in directing the new fields into different angular positions, especially for the zeroth-order diffraction. A number of interesting features appears in the shaped two-photon wave forms. For example, broadening or narrowing the spectrum would be possible in the proposed scheme even without the use of a cavity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Four-wave mixing in a three-level bichromatic electromagnetically induced transparency system

We investigate the four-wave mixing (FWM) phenomenon in a three-level bichromatic electromagnetically induced transparency system. Theoretical results predict that the FWM will exhibit a multipeak structure under bichromatic coupling fields. The stronger the coupling fields are, the more FWM the peaks should exhibit. Results of an experiment carried out with cold {sup 87}Rb atoms in a magneto-optical trap agree with the theoretical prediction.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Effect of buffer gas on an electromagnetically induced transparency in a ladder system using thermal rubidium vapor

We report on the observation of electromagnetically induced transparency in a ladder system in the presence of a buffer gas. In particular, we study the 5S{sub 1/2}-5P{sub 3/2}-5D{sub 5/2} transition in thermal rubidium vapor with a neon buffer gas at a pressure of 6 Torr. In contrast to the line-narrowing effect of buffer gas on {Lambda} systems, we show that the presence of the buffer gas leads to an additional broadening of (34{+-}5) MHz, which suggests a cross section for Rb(5D{sub 5/2})-Ne of {sigma}{sub k}{sup (D)}=(23{+-}4)x10{sup -19} m{sup 2}. However, in the limit where the coupling Rabi frequency is larger than the collisional dephasing, a strong transparency feature can still be observed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Scalable network of quadrangle entanglements via multiple phase-dependent electromagnetically induced transparency

One important class of multipartite continuous variable entanglement is described by a closed polygon, where every vertex represents one optical field and every side corresponds to the entanglement between the two connected vertices. Here we show that it is possible to obtain a scalable network of quadrangle entanglements by using multiple phase-dependent electromagnetically induced transparency. For 4,6,8,...,2n (n{>=}2) mode cases the network consists of 1,9,36,...,(1/4)n{sup 2} (n-1){sup 2} quadrangles, respectively. This suggests an efficient way of creating complex quantum networks and has great potentials for quantum information and computation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Interpreting quantum states of electromagnetic field in time-dependent linear media

Recently, Pedrosa and Rosas [Phys. Rev. Lett. 103, 010402 (2009)] investigated the quantum states of an electromagnetic field in time-dependent linear media using a Hermitian linear invariant. The wave function obtained by them is represented in terms of an arbitrary weight function g({lambda}{sub l}). Since the type of wave function varies depending on the choice of g({lambda}{sub l}) in their problem, it may be a difficult task to construct a coherent state that resembles the classical state from their theory. We suggest, on the basis of a non-Hermitian linear invariant, another quantum state that is a kind of coherent state. The expectation value of canonical variables in this alternate state follows an exact classical trajectory. For a simple case in which the time dependence of the parameters {epsilon}(t), {mu}(t), and {sigma}(t) disappears, we showed that the quantum energy expectation value in the alternate quantum state recovers exactly to the classical energy in the limit ({h_bar}/2{pi}){yields}0. This alternate state leads to the correspondence between the quantum and the classical behaviors of physical observables in a high-energy limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Electromagnetically induced conical emission

We describe theoretically a scheme for observing conical emission, a transverse nonlinear optical effect, in an atomic vapor with all excitation fields below the saturation level of the involved atomic transitions. The scheme relies on the giant Kerr nonlinearities possible under electromagnetically induced transparency to introduce a radially varying phase shift to a weak probe field by a weak signal field. The probe's far-field diffraction pattern shows multiple concentric rings around the probe beam's axis, characteristic of conical emission.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Electromagnetically induced transparency without a Doppler background in a multilevel ladder-type cesium atomic system

We present an investigation of electromagnetically induced transparency (EIT) without Doppler background due to a locked probe laser. The EIT is theoretically studied based on a multilevel ladder-type cesium atomic system 6S{sub 1/2}-6P{sub 3/2}-8S{sub 1/2} in a room-temperature vapor cell. The experimental results agree with the theoretical calculations. Compared with the traditional EIT spectra with a Doppler profile limiting the spectral resolution for keeping the coupling laser locked and scanning the probe laser, these EIT spectra with the probe laser locked and the coupling laser scanned have a flat background, which seem be of great benefit for applications such as the measurement of hyperfine intervals between excited states, the study of highly excited Rydberg states, laser-frequency stabilization, etc.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Electromagnetically induced transparency in paraffin-coated vapor cells

Antirelaxation coatings in atomic vapor cells allow ground-state coherent spin states to survive many collisions with the cell walls. This reduction in the ground-state decoherence rate gives rise to ultranarrow-bandwidth features in electromagnetically induced transparency (EIT) spectra, which can form the basis of, for example, long-time scale slow and stored light, sensitive magnetometers, and precise frequency standards. Here we study, both experimentally and theoretically, how Zeeman EIT contrast and width in paraffin-coated rubidium vapor cells are determined by cell and laser-beam geometry, laser intensity, and atomic density. Using a picture of Ramsey pulse sequences, where atoms alternately spend ''bright'' and ''dark'' time intervals inside and outside the laser beam, we explain the behavior of EIT features in coated cells, highlighting their unique characteristics and potential applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Measurements of the magnetic field vector using multiple electromagnetically induced transparency resonances in Rb vapor

We study the dependence of electromagnetically induced transparency (EIT) resonance amplitudes on the external magnetic field direction in a linearly polarized bichromatic light (lin||lin) configuration in {sup 87}Rb vapor. We demonstrate that all seven resolvable EIT resonances exhibit maxima or minima at certain orientations of the laser polarization relative to the wave vector and magnetic field. This effect can be used for the development of a high-precision EIT vector magnetometer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Electromagnetic vacuum of complex media: Dipole emission versus light propagation, vacuum energy, and local field factors

We offer a unified approach to several phenomena related to the electromagnetic vacuum of a complex medium made of point electric dipoles. To this aim, we apply the linear response theory to the computation of the polarization field propagator and study the spectrum of vacuum fluctuations. The physical distinction among the local density of states which enter the spectra of light propagation, total dipole emission, coherent emission, total vacuum energy, and Schwinger-bulk energy is made clear. Analytical expressions for the spectrum of dipole emission and for the vacuum energy are derived. Their respective relations with the spectrum of external light and with the Schwinger-bulk energy are found. The light spectrum and the Schwinger-bulk energy are determined by the Dyson propagator. The emission spectrum and the total vacuum energy are determined by the polarization propagator. An exact relationship of proportionality between both propagators is found in terms of local field factors. A study of the nature of stimulated emission from a single dipole is carried out. Regarding coherent emission, it contains two components. A direct one which is transferred radiatively and directly from the emitter into the medium and whose spectrum is that of external light. And an indirect one which is radiated by induced dipoles. The induction is mediated by one (and only one) local field factor. Regarding the vacuum energy, we find that in addition to the Schwinger-bulk energy the vacuum energy of an effective medium contains local field contributions proportional to the resonant frequency and to the spectral line width.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Simultaneous electromagnetically induced transparency for two circularly polarized lasers coupled to the same linearly polarized laser in a four-level atomic system in the W scheme

Electromagnetic induced transparency (EIT) can be produced in a four-level atomic system in the W scheme using a linearly polarized optical field for simultaneously slowing down two {sigma}{sup +} and {sigma}{sup -} circularly polarized optical fields. This four-level atomic system can be set up with a |{sup 1}S{sub 0}> ground state and three Zeeman levels of the |{sup 1}P{sub 1}> excited state of any alkali-metal atom placed in a weak magnetic field. We apply our W scheme to ultracold magnesium atoms for neglecting the collisional dephasing. Atomic coherences are reported after solving a density matrix master equation including radiative relaxations from Zeeman states of the |{sup 1}P{sub 1}> multiplet to the |{sup 1}S{sub 0}> ground state. The EIT feature is analyzed using the transit time between the normal dispersive region and the EIT region. The evolution of the EIT feature with the variation of the coupling field is discussed using an intuitive dressed-state representation. We analyze the sensitivity of an EIT feature to pressure broadening of the excited Zeeman states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Electromagnetically induced transparency in a five-level {Lambda} system dominated by two-photon resonant transitions

We study the steady optical response of a five-level atomic system in the parametric region where resonant two-photon transitions are much stronger than far-detuned single-photon transitions. We find that the concurrent absorption of two weak probe fields can be well suppressed in a narrow spectral region to attain electromagnetically induced transparency (EIT) via quantum destructive interference between different two-photon transition pathways. To gain a deeper insight into relevant physics, we adiabatically reduce this five-level system with trivial single-photon transitions into a three-level system with vanishing single-photon transitions by deriving an effective Hamiltonian. The two systems have almost the same two-photon absorption spectra exhibiting typical EIT features but are a little different in fine details. This means that most characteristics of two-photon quantum destructive interference are reserved after the adiabatic elimination approximation. In addition, we verify by numerical calculations that the two-photon EIT spectra are insensitive to the dipole-dipole interaction of cold Rydberg atoms when the uppermost level has a high principle quantum number.

74 ATOMIC AND MOLECULAR PHYSICS↗