Electrodynamic Phenomena Research Articles

High-Precision Metrology of Highly Charged Ions via Relativistic Resonance Fluorescence

Resonance fluorescence of laser-driven highly charged ions is investigated with regard to precisely measuring atomic properties. For this purpose an ab initio approach based on the Dirac equation is employed that allows for studying relativistic ions. These systems provide a sensitive means to test correlated relativistic dynamics, quantum electrodynamic phenomena and nuclear effects by applying x-ray lasers. We show how the narrowing of sidebands in the x-ray fluorescence spectrum by interference due to an additional optical driving can be exploited to determine atomic dipole or multipole moments to unprecedented accuracy.

Efficient evaluation of Casimir force in arbitrary three-dimensional geometries by integral equation methods

In this Letter, we generalized the surface integral equation method for the evaluation of Casimir force in arbitrary three-dimensional geometries. Similar to the two-dimensional case, the evaluation of the mean Maxwell stress tensor is cast into solving a series of three-dimensional scattering problems. The formulation and solution of the three-dimensional scattering problems are well-studied in classical computational electromagnetics. This Letter demonstrates that this quantum electrodynamic phenomenon can be studied using the knowledge and techniques of classical electrodynamics.

Damage self-diagnoses feasibility of fiber-reinforced concrete structure

The seepage theory was used to explain the variation between the specific resistance of the carbon fiber reinforced cement concrete and the carbon fiber volume ratio. The electro-dynamic seepage was observed in the cement. The longer the carbon fiber is, the smaller the critical volume to produce the electro-dynamic seepage phenomenon will be. However, the forming and stirring process is harder. In general, the average length of carbon fiber is 5 mm. Under the condition of three-point bending load, the specific resistance changes with the loading process, and a good correlation could be obtained according to the load-deflection relationship. The experimental results reveal that the carbon fiber reinforced cement based composites can be used as sensors to self-diagnoses of the damage.

Evidence against Klein paradox in graphene

It is demonstrated that both transmission and reflection coefficients associated with the Klein paradox at a step barrier are positive and less than unity, so that the particle-antiparticle pair creation mechanism commonly linked to this phenomenon is not necessary. Because graphene is a solid-state testing ground for quantum electrodynamics phenomena involving massless Dirac fermions, we suggest that the transport characteristic through a p–n graphene junction can decide between the results obtained in this paper and the common Klein paradox theory, which imply negative transmission and higher-than-unity reflection coefficients. Recent experimental evidence supports our findings.

A theoretical model for mid- and low-latitude ionospheric electric fields in realistic geomagnetic fields

The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.

Casimir Forces and Quantum Electrodynamical Torques: Physics and Nanomechanics

This paper discusses recent developments on quantum electrodynamical (QED) phenomena, such as the Casimir effect, and their use in nanomechanics and nanotechnology in general. Casimir forces and torques arise from quantum fluctuations of vacuum or, more generally, from the zero-point energy of materials and their dependence on the boundary conditions of the electromagnetic fields. Because the latter can be tailored, this raises the interesting possibility of designing QED forces for specific applications. After a concise review of the field in an historical perspective, high precision measurements of the Casimir force using microelectromechanical systems (MEMS) technology and applications of the latter to nonlinear oscillators are presented, along with a discussion of its use in nanoscale position sensors. Then, experiments that have demonstrated the role of the skin-depth effect in reducing the Casimir force are presented. The dielectric response of materials enters in a nonintuitive way in the modification of the Casimir-Lifshitz force between dielectrics through the dielectric function at imaginary frequencies epsiv(ixi). The latter is illustrated in a dramatic way by experiments on materials that can be switched between a reflective and a transparent state (hydrogen switchable mirrors). Repulsive Casimir forces between solids separated by a fluid with epsiv(ixi) intermediate between those of the solids over a large frequency range is discussed, including ongoing experiments aimed at its observation. Such repulsive forces can be used to achieve quantum floatation in a virtually frictionless environment, a phenomenon that could be exploited in innovative applications to nanomechanics. The last part of the paper deals with the elusive QED torque between birefringent materials and efforts to observe it. We conclude by highlighting future important directions

On the Material Invariant Formulation of Maxwell’s Displacement Current

Maxwell accounted for the apparent elastic behavior of the electromagnetic field by augmenting Ampere’s law with the so-called displacement current, in much the same way that he treated the viscoelasticity of gases. Maxwell’s original constitutive relations for both electrodynamics and fluid dynamics were not material invariant. In the theory of viscoelastic fluids, the situation was later corrected by Oldroyd, who introduced the upper-convective derivative. Assuming that the electromagnetic field should follow the general requirements for a material field, we show that if the upper convected derivative is used in place of the partial time derivative in the displacement current term, Maxwell’s electrodynamics becomes material invariant. Note, that the material invariance of Faraday’s law is automatically established if the Lorentz force is admitted as an integral part of the model. The new formulation ensures that the equation for conservation of charge is also material invariant in vacuo. The viscoelastic medium whose apparent manifestation are the known phenomena of electrodynamics is called here the metacontinuum.

Problems of the physics of geoelectromagnetic waves (a review)

Relevant tasks, disputable issues, and unsettled problems of the physics of ultralow-frequency electromagnetic waves of natural origin (a period range of 0.2–600 s) are discussed in the paper. Waves excited by intra-and extraterrestrial sources are considered. Subjects associated with some closely interrelated problems in the physics of both the solid and plasma shells of the planet are discussed. Common features of electrodynamic phenomena in geophysical media are emphasized. It is inferred that recent progress in the investigation of ultralow-frequency waves does not eliminate the necessity for careful study of unsolved problems posed in the past.

Quantum vacuum properties of the intersubband cavity polariton field

We present a quantum description of a planar microcavity photon mode strongly coupled to a semiconductor intersubband transition in presence of a two-dimensional electron gas. We show that, in this kind of system, the vacuum Rabi frequency ${\ensuremath{\Omega}}_{R}$ can be a significant fraction of the intersubband transition frequency ${\ensuremath{\omega}}_{12}$. This regime of ultrastrong light-matter coupling is enhanced for long-wavelength transitions, because for a given doping density, effective mass and number of quantum wells, the ratio ${\ensuremath{\Omega}}_{R}∕{\ensuremath{\omega}}_{12}$ increases as the square root of the intersubband emission wavelength. We characterize the quantum properties of the ground state (a two-mode squeezed vacuum), which can be tuned in situ by changing the value of ${\ensuremath{\Omega}}_{R}$, e.g., through an electrostatic gate. We finally point out how the tunability of the polariton quantum vacuum can be exploited to generate correlated photon pairs out of the vacuum via quantum electrodynamics phenomena reminiscent of the dynamical Casimir effect.

Strong exciton‐light coupling in photonic crystal nanocavities

The strong coupling regime between excitons in a single self-assembled InAs quantum dot and the cavity mode in a photonic-crystal structure embedded in GaAs planar waveguides is theoretically investigated. It is concluded that zero-dimensional mixed states should form when the quality factor of the cavity mode is higher than Q ∼ 2000. The corresponding vacuum-field Rabi splitting is close to its limiting value already for Q ∼ 10000. Results are shown for a model GaAs-based photonic crystal nanocavity, in which single quantum dot excitons are predicted to be always in the strong coupling regime if the quantum dot is placed close to the antinode position of the electric field. 1 Introduction Photonic crystals (PhC) embedded in planar dielectric waveguides (also known as photonic-crystal slabs) allow for a three-dimensional (3D) control of light confinement and propagation at optical wavelengths, and are currently receiving much attention owing to the difficulties in fabricating 3D PhC with robust band gaps in the visible region (for a recent review see [1]). In PhC slabs the electromagnetic field can be confined in 3D by exploiting the photonic band gap properties in the plane of the waveguide and the confinement provided by the strong dielectric contrast along the vertical direction. By creating localized defects in the otherwise periodic structures, PhC nanocavities with cavity mode energies falling within the photonic band gap can be obtained. Very small mode volumes and ultra-high quality (Q) factors have been recently demonstrated for cavity modes in thin air-suspended Silicon slabs (also called air bridges) with point defects in a triangular lattice of air holes [2]. Thus, these systems appear as ideal candidates for the observation of the strong coupling regime and other interesting cavity quantum electrodynamics phenomena in photonic nanostructures.

Electrodynamics of Magnetoactive Media

`Electrodynamics of Magnetoactive Media' is an unusual book in that it cuts across conventional physics discipline boundaries. The unifying theme allowing this is, quite simply, the physics of magnetic fields in various media. I believe the authors are correct in stating that the book is unique in specifically covering electrodynamic phenomena associated with magnetic fields, though of course some of the more elementary aspects are covered in the classical textbooks on electromagnetism, which are duly acknowledged. This interdisciplinarity makes the book very interesting to people with a range of backgrounds. For example, as a plasma physicist, I was familiar with most of the material on plasmas, but liquid crystals and superconductors were entirely new territory for me. These chapters were indeed both accessible and interesting, and it was surprising for me to see how much commonality there is in the physics of these various media. The first part of the book covers some fundamentals of electrodynamics and magnetostatics, and of electromagnetic waves. Most of this material is covered in textbooks on electromagnetism, and some of it is very basic (for example, LRC circuit theory, surely covered in most first year physics courses, is included) but it is perhaps a useful prelude for what is to come. The generic topic of charged particle motion in electromagnetic fields is well covered. Three main magnetoactive media are then discussed: plasmas (focusing on waves), liquid crystals and superconductors. It is all too easy to criticise a book on the grounds of omitted material, but I do feel that a chapter on magnetostatics in plasmas would have been very helpful, covering force-free fields and so on. Some interesting analogies could then have been exploited. For example, I was intrigued to discover an equation for magnetic fields in superconductors (equation (9.36)) which, apart from a change of sign, is identical to the Helmholtz equation used to\newpage\noindent model linear force-free fields in plasmas. Even more intriguingly, the mathematical solution then developed for a junction between a normal conductor and a superconductor is then almost identical to a solution I once published for the equilibrium of expanding plasma loops in the solar corona! The book is clearly written, and the level of mathematics is very appropriate for an advanced undergraduate or postgraduate text: the authors do not fall into the trap of superficially simplifying the description by omitting steps of mathematical arguments. It is a pity, however, that there are no examples or problems, ideally with solutions, which would have been very helpful if the book were to be used for teaching purposes. Nevertheless, because of the interdisciplinarity and the emphasis on fundamental physical principles unifying diverse applications, this book would be a very good basis for a course. Perhaps academics will be encouraged to introduce new lecture courses on this interesting topic. Every library should have a copy of this book, and it would be of interest to many individual researchers who would like to broaden their knowledge outside their own research fields.

Sculpting the vacuum in a photonic band gap micro-chip

We describe the engineering of the electromagnetic vacuum in a 2D–3D photonic bandgap (PBG) hetero-structure. This facilitates the development of novel active devices and the observation of novel quantum electrodynamic phenomena. We consider a specific architecture suitable as an all-optical micro-transistor capable of novel ultra-fast response with low switching power requirements. This relies on a unique collective atomic switching and population inversion achieved by coherent resonant pumping in a suitably engineered vacuum. Specific waveguide architectures within the 3D PBG micro-chip provide local density-of-states (LDOS) peaks near their cutoff frequency. These provide “building blocks” for electromagnetic vacuum engineering without recourse to conventional high Q-factor micro-cavities. For the all-optical micro-transistor, a fork shape LDOS within the micro-chip is desirable, using trimodal waveguide architecture. We delineate the functional robustness of these architectures to disorder caused by manufacturing errors within the PBG micro-chip.

Ritz, Einstein, and the Emission Hypothesis

Just as Albert Einstein’s special theory of relativity was gaining acceptance around 1908, the young Swiss physicist Walter Ritz advanced a competing though preliminary emission theory that sought to explain the phenomena of electrodynamics on the assumption that the speed of light depends on the motion of its source. I survey Ritz’s unfinished work in this area and review the reasons why Einstein and other physicists rejected Ritz’s and other emission theories. Since Ritz’s emission theory attracted renewed attention in the 1960s, I discuss how the earlier observational evidence was misconstrued as telling against it more conclusively than actually was the case. Finally, I contrast the role played by evidence against Ritz’s theory with other factors that led to the early rejection of his approach.

The sink for outer belt electrons and the electrodynamics of the middle atmosphere

The middle atmosphere at the foot of the geomagnetic field lines of the outer belt of trapped radiation (about L=4) is a region of dramatically variable electron precipitation. Consequently, electrodynamic phenomena in the atmosphere of this region exhibit significant variation. Typically, the electron population of the outer belt increases by several orders of magnitude during geomagnetic activity associated with the passage of a solar sector boundary; then, over the course of the following week or so, this enormous quantity of trapped electrons precipitates into the atmosphere. However, due to the geometry of the geomagnetic field, this electron precipitation is not distributed evenly: it is concentrated in the sink for outer belt electrons in Antarctica above the Weddell Sea. This “sink” occurs because trapped electrons are scattered to lower equatorial pitch angles by wave–particle interactions. Individual scattering events are smaller than the longitudinal, or hemispheric, variations in the equatorial pitch angle at which electrons are lost into the atmosphere, thus precipitation occurs around 0° longitude in the southern hemisphere for eastward drifting trapped electrons. West of this location, electrons can be temporarily trapped at smaller equatorial pitch angles, but eastward drift transports these particles into the atmosphere, a phenomenon referred to as the drift loss cone. The diurnal modulation of electron precipitation induced by the effect of the dawn-to-dusk geoelectric field is discussed, as well. Experimental data that support this model of electron precipitation are presented. Also, the effect of the outer belt electron sink on the chemistry of the middle atmosphere is introduced.

Electric launch science and technology in the United States

For electromagnetic launchers, most of the effort is directed toward improved computational tools, exploitation of these tools for detailed understanding of transient electrodynamic phenomena, novel diagnostics, and experiments to resolve remaining critical issues such as transition from solid to arc contacts in railguns, improved computational techniques for pulsed power systems, and application of these tools to design new high-energy pulsed-power sources. New methods of testing and determining the critical properties of advanced materials, such as composites, are being developed to enable these materials to be evaluated in extreme thermal and electromechanical environments. Additionally, the U.S. Navy is also in the process of initiating hypervelocity electromagnetic launch efforts for extremely long-range artillery systems employing high-G novel projectiles. Other applications of electric launch technology, such as hypervelocity powder deposition and electromagnetic gun launch to space, continue to offer new and interesting opportunities.

Computational modeling of electrodynamic and transport phenomena in materials processing systems

This paper discusses the numerical modeling of coupled electromagnetic and transport (fluid flow and heat and mass transfer) phenomena in materials processing systems under both terrestrial and microgravity conditions. Two types of magnetically induced transport phenomena are considered and both require iterative numerical computations. For the former, the flow is activated through Faraday's law and the computational methodology entails the use of the boundary element method to model the free space region and of the finite element method to model the interior region of the liquid. Computations involve the iterative solution of magnetic fields, fluid flow and surface stress balance when free surface deformation occurs. For the later, the fluid motion is suppressed by an applied DC magnetic field and flow and magnetic fields are coupled so that iterative computational procedure is again required. For this later case, computational costs are substantially reduced by carefully designing the finite element global matrix structure.

Optimization of three-dimensional micropost microcavities for cavity quantum electrodynamics

This article presents a detailed analysis, based on the first-principles finite-difference time-domain method, of the resonant frequency, quality factor (Q), mode volume (V), and radiation pattern of the fundamental (HE11) mode in a three-dimensional distributed-Bragg-reflector (DBR) micropost microcavity. By treating this structure as a one-dimensional cylindrical photonic crystal containing a single defect, we are able to push the limits of Q/V beyond those achievable by standard micropost designs, based on the simple rules established for planar DBR microcavities. We show that some of the rules that work well for designing large-diameter microposts (e.g., high-refractive index contrast) fail to provide high-quality cavities with small diameters. By tuning the thicknesses of mirror layers and the spacer, the number of mirror pairs, the refractive indices of high and low refractive index regions, and the cavity diameter, we are able to achieve Q as high as 10^4, together with a mode volume of 1.6 cubic wavelengths of light in the high-refractive-index material. The combination of high Q and small V makes these structures promising candidates for the observation of such cavity quantum electrodynamics phenomena as strong coupling between a quantum dot and the cavity field, and single-quantum-dot lasing.

Experimental investigation of creep and the recovery behaviours of magnetorheological fluids

This paper presents an analytical study on the transient electrodynamic and fluid flow phenomena in a magnetically-levitated liquid sphere. Using the method of separation of variables, analytical solutions are derived for the transient electromagnetic field inside and outside the sphere in the form of the magnetic vector potential, and the fluid flow field in terms of the stream function, respectively. Both asymptotic and detailed analyses are described. It is found that the decay of a levitation system is characterized by three quite different time scales: one for the electromagnetic field, one for the fluid flow field, and one for the thermal field. The electromagnetic field decays several orders of magnitude faster than either the fluid flow field or the temperature field, and therefore its effect can be well ignored when the flow and/or thermal fields are considered. The ratios of these time scales may be related to the nondimensional system numbers that characterize the system. Detailed calculations show that when started from a symmetric velocity field, the decay results in a reduction of the velocity level but the flow pattern remains unchanged, whereas the evolution from an asymmetric flow field involves both a diminution in the velocity level and a change in the flow pattern. The two decaying processes are also characterized by different time scales, with the one for the asymmetric case being larger. Application of the analyses to design and control the experiments of undercooling and/or free surface oscillations under microgravity is also discussed. It is found that an undercooling of a desired degree may be obtained free from the internal flow influence if an appropriate starting temperature is chosen for the experiment. It is also possible to carry out the experiments of free surface oscillation without the interference from the internal flow; however, careful control is needed to maintain the liquid at a relatively constant temperature.

A macro/micro model for magnetic stirring and microstructure formation during solidification

An integrated macro/micro model is developed to represent the evolution of complex electrodynamic and transport phenomena and solidification microstructures in solidifying metals with electromagnetic stirring. The model development is based on the hybrid boundary/finite element solution of the Maxwell equations and the finite element (FE) solution of the momentum and thermal transport equations, in combination with the Monte-Carlo-cellular-automaton representation of the evolution of solidification microstructure formation. In applying the FE method for flow calculations, pressure is treated using the standard reduced penalty approximation and the phase interaction effects by the Carman–Kozney equation. A sub-level time and space scheme is developed to effectively integrate the macro- and micro-scale simulations. To enhance the computational speed, the microstructure formation simulations are carried out in parallel using the Parallel Virtual Machine library. The model is applied to simulate the electrodynamic, fluid flow and heat transfer phenomena and microstructure formation in a cavity surrounded by induction coils. Results show that magnetically induced stirring can have pronounced effects on the evolution of microstructure during solidification.

Surface roughness contribution to the Casimir interaction between an isolated atom and a cavity wall

An approximate perturbative method is developed to calculate the corrections to the Casimir force between an isolated atom and a cavity wall due to surface roughness. The results are obtained up to the fourth order in the relative roughness amplitude. All possible types of surface roughness are considered: large scale, short scale, and intermediate, defined by the ratio of the characteristic lateral length scale of roughness to the atom-wall distance. A continuous transition between the corrections due to different types of roughness is carried out. It is shown that the large-scale roughness can lead to corrections of the order of 70% of the net Casimir force. In the cases of large-scale and intermediate-type roughness the lateral Casimir force comes into play, which leads to moving the atom to the nearest extreme point of the vertical force with subsequent dying out oscillations in its vicinity. Possible role wall roughness can play in some phenomena of cavity electrodynamics is discussed.