Dispersive Dielectric Medium Research Articles

A Novel Method for Sensing Local Electron Density via Measuring the VSWR of Spaceborne Antenna

The performance of an antenna is impacted by the electromagnetic characteristics of the media surrounding the antenna. Most antennas work in neutral air. However, the surrounding media for the spaceborne antenna is space plasma, which is dispersive dielectric media. It could significantly change the performance of a spaceborne broadband antenna. In the present study, a broadband dipole antenna was taken for example to investigate the impacts led by space plasma. The working parameters in neutral air and space plasma were compared. The space plasma taken into account in the present study was supposed to be time-varying dispersive media. The study revealed that the space plasma could significantly influence the antenna voltage standing wave ratio (VSWR) and the antenna impedance. For those spaceborne radars working in active mode, there was a minimum detection range which makes it hard to detect the plasma area within the range. Since antenna working parameters vary with the variation of the surrounding plasma, a method to sensing the local plasma electron density based on VSWR of spaceborne broadband antennas was proposed. The method makes the antenna system work as a plasma sensor and could complement the radar minimum detection range. The results show the good performance of the method.

A Realistic Interpretation of Quantum Wavefunctions as Temperature Dependent Vacuum Polarization Waves

We discuss in this paper a novel interpretation of Born rule as an approximated thermodynamic law which emerges from the interaction of a quantum system with a non-stationary thermal bath associated to vacuum fluctuations induced by external environment radiation. In particular we assume that vacuum polarization is a real non relativistic phenomena caused by hidden vacuum charge oscillations which diffuses heat energy in a dispersive and dissipative dielectric medium with a temperature dependent speed of propagation. We propose a model which couples vacuum wavefunctions to vacuum charge fluctuations and we deduce a temperature dependent running fine structure constant function proportional, at first approximation, to the squared of the effective electron charge and compatible with known experimental data. We interpret the vacuum symmetry breaking energy fluctuations induced in scattering experiments of particle physics and in laser assisted nuclear reactions as thermal quasi-monochromatic beams produced by the decay of hidden non equilibrium massive photons propagating with a variable light speed. We suggest, exploiting an old analogy between plasmons and pseudo Goldstone bosons, to interpret heat diffusion of this non relativistic polarized vacuum as a real De Broglie electromagnetic scalar wave associated to the radiation emitted by the hidden massive photons with acceleration proportional to vacuum Unruh like temperature. We predict a temperature dependent deviation from Coulomb law and a generalized dispersive law of these hidden unstable photons that could be revealed as not stationary coloured noise in experiments on anomalous heat diffusions associated to the decay of unstable accelerated pairs produced in nuclear physics experiments. We discuss then how our proposal of a temperature dependent non relativistic vacuum polarization might be applied to deduce a dynamic generalization of Born rule based on a realistic interpretation of quantum wavefunctions as averaged electromagnetic waves of hidden massive photons. Finally we suggest to test our time asymmetric model looking for very fast oscillating polarization thermal waves emitted during the not instantaneous wavefunction collapse and revealed as not stationary bulk heating effects in experiments on accelerated conductors and nanoconductors.

Analogous Hawking Effect in Dielectric Media and Solitonic Solutions

We review some aspects of our longstanding research concerning the analogous Hawking effect in dispersive dielectric media. We introduce nonlinear contributions in the polarization field in the relativistically covariant version of the Hopfield model and then, in order to provide a simplified description aimed at avoiding some subtleties in the quantization of the original model, we discuss the so-called ϕψ-model. We show that the nonlinearity allows for introducing in a self-consistent way the otherwise phenomenological dependence of the susceptibility and of the resonance frequency ω0 on the spacetime variables, and this is a consequence of the linearization of the model around solitonic solutions representing propagating perturbations of the refractive index, to be then associated with the Hawking effect.

On the nature of the Sommerfeld–Brillouin forerunners (or precursors)

We present a brief overview of Sommerfeld's forerunner signal, which occurs when a monochromatic plane-wave (frequency {\omega}={\omega}_s) suddenly arrives, at time t=0 and at normal incidence, at the surface of a dispersive dielectric medium of refractive index n({\omega}). Deep inside the dielectric host at a distance z0 from the surface, no signal arrives until t=z0/c, where c is the speed of light in vacuum. Immediately after this point, a weak but extremely high frequency signal is observed at z=z0. This so-called Sommerfeld forerunner (or precursor) is highly chirped, meaning that its frequency, which is much greater than {\omega}_s immediately after t=z0/c, declines rapidly with the passage of time. The incident light with its characteristic frequency {\omega}_s eventually arrives at t~z0/vg , where vg is the group velocity of the incident light inside the host medium. Brillouin has identified a second forerunner that occupies the interval between the end of the Sommerfeld forerunner at t~n(0)z0/c and the beginning of the steady signal. This second forerunner is commonly referred to as the Brillouin forerunner (or precursor). Given that the incident wave has a sudden start at t=0, its frequency spectrum spans the entire range of frequencies from minus infinity to infinity. Consequently, the high-frequency first forerunner cannot be considered a superoscillation, nor can the low-frequency second forerunner be regarded as a suboscillation. The goal of the present paper is to extend the Sommerfeld-Brillouin theory of precursors to bandlimited incident signals, in an effort to determine the conditions under which these precursors would continue to exist, and to answer the question as to whether or not such precursors, upon arising from a bandlimited incident signal, constitute super- or sub-oscillations.

Equivalence between the Hamiltonian and Langevin noise descriptions of plasmon polaritons in a dispersive and lossy inhomogeneous medium

We demonstrate the fundamental links existing between two different descriptions of quantum electrodynamics in inhomogeneous, lossy and dispersive dielectric media which are based either on the Huttner-Barnett formalism for polaritons [B. Huttner and S. M. Barnett, Phys.Rev. A 46, 4306 (1992)] or the Langevin noise approach using fluctuating currents [T. Gruner and D.-G. Welsch, Phys.Rev.A 53, 1818 (1996)]. In this work we demonstrate the practical equivalence of the two descriptions by introducing the concept of effective photon state associated with some specific noise current distribution. We study the impact of these results on the calculation and interpretation of quantum observables such as fluctuations, correlations, and Casimir forces.

Derivation of Hawking radiation in dispersive dielectric media

Motivated by recent experimental efforts, we study a black hole analog induced by the propagation of a strong laser pulse in a nonlinear dielectric medium. Based on the Hopfield model (one pair of Sellmeier coefficients), we perform an analytic and fully relativistic microscopic derivation of the analog of Hawking radiation in this setup. The Hawking temperature is determined by the analog of the surface gravity (as expected), but we also find a frequency-dependent gray-body factor (i.e., a nonthermal spectrum at infinity) due to the breaking of conformal invariance in this setup.

Perturbative photon production in a dispersive medium

We investigate photon pair-creation in a dispersive dielectric medium induced by the presence of a spacetime varying dielectric constant. Our aim is to examine the possibility to observe new phenomena of pair creation induced by travelling dielectric perturbations e.g. created by laser pulses by means of the Kerr effect. In this perspective, we adopt a semi-phenomenological version of the Hopfield model in which a space-time dependent dielectric susceptibility appears. We focus our attention on perturbation theory, and provide general formulas for the photon production induced by a local but arbitrarily spacetime dependent refractive index perturbation. As an example, we further explore the case of a uniformly travelling perturbation, and provide examples of purely time-dependent perturbations.

Thermal balance and photon-number quantization in layered structures

The quantization of the electromagnetic field in lossy and dispersive dielectric media has been widely studied during the last few decades. However, several aspects of energy transfer and its relation to consistently defining position-dependent ladder operators for the electromagnetic field in nonequilibrium conditions have partly escaped the attention. In this work we define the position-dependent ladder operators and an effective local photon-number operator that are consistent with the canonical commutation relations and use these concepts to describe the energy transfer and thermal balance in layered geometries. This approach results in a position-dependent photon-number concept that is simple and consistent with classical energy conservation arguments. The operators are formed by first calculating the vector potential operator using Green's function formalism and Langevin noise source operators related to the medium and its temperature, and then defining the corresponding position-dependent annihilation operator that is required to satisfy the canonical commutation relations in arbitrary geometry. Our results suggest that the effective photon number associated with the electric field is generally position dependent and enables a straightforward method to calculate the energy transfer rate between the field and the local medium. In particular, our results predict that the effective photon number in a vacuum cavity formed between two lossy material layers can oscillate as a function of the position suggesting that also the local field temperature oscillates. These oscillations are expected to be directly observable using relatively straightforward experimental setups in which the field-matter interaction is dominated by the coupling to the electric field. The approach also gives further insight on separating the photon ladder operators into the conventional right and left propagating parts and on the anomalies reported for the commutation relations of the corresponding operators within optical cavities.

Transition radiation of a charged particle crossing the waveguide filled with a dispersive dielectric medium perpendicularly to the waveguide axis

The theory of charged particle transition radiation is developed for the case when the particle crosses the waveguide, which is filled with a piecewise-homogeneous dielectric, perpendicularly to the waveguide axis. The cases where the charged particle is flying between two dispersive plates and between two thin impedance films are considered.

Electromagnetic energy, absorption, and Casimir forces. II. Inhomogeneous dielectric media

A general, exact formula is derived for the expectation value of the electromagnetic energy density of an inhomogeneous absorbing and dispersive dielectric medium in thermal equilibrium, assuming that the medium is well approximated as a continuum. From this formula we obtain the formal expression for the Casimir force density. Unlike most previous approaches to Casimir effects in which absorption is either ignored or admitted implicitly through the required analytic properties of the permittivity, we include dissipation explicitly via the coupling of each dipole oscillator of the medium to a reservoir of harmonic oscillators. We obtain the energy density and the Casimir force density as a consequence of the van der Waals interactions of the oscillators and also from Poynting's theorem.

EXTREMELY SHORT OPTICAL PULSES IN CARBON NANOTUBES IN DISPERSIVE NONMAGNETIC DIELECTRIC MEDIA

We consider Maxwell equations for an electromagnetic field propagating in carbon nanotubes (CNTs) placed on a dispersive nonmagnetic dielectric medium. We obtain the effective equation analogous to the classical sine-Gordon equation. Then it has been analyzed numerically. We have revealed the dependence of the pulse on the type of CNT and on the initial pulse amplitude, as well as on the medium dispersion constants.

On the role of dissipation on the Casimir–Polder potential between molecules in dielectric media

An expression for the Casimir-Polder potential between molecules in a homogeneous dispersive and absorptive dielectric medium is derived. The effect of retardation on the interaction energy is discussed by examining the wave-zone and nonretarded limits of the potential. Unlike Lifshitz theory, the interaction energy is not derived from the potential between macroscopic bodies. In this work, a Green function that explicitly accounts for absorption in the medium is obtained. This function leads to possible dissipation effects and presents a near-zone form that vanishes in the limit of nonabsorptive medium. Employing a two-level model, it is shown that the retarded van der Waals dispersion potential in a medium may become repulsive as a consequence of absorption by the medium. It is suggested that the repulsive dispersion force may delay precipitation of nonpolar molecules from a dielectric solvent or even inhibit chemical reaction between them.

Controlling metamaterial resonances with light

We investigate the use of coherent optical fields as a means of dynamically controlling the resonant behaviour of a variety of composite metamaterials, wherein the metamaterial structures are embedded in a dispersive dielectric medium. Control and switching is implemented by coherently driving the resonant permittivity of the embedding medium by applied optical radiation. The effect of embedding Split ring resonators (SRR) in a frequency- dispersive medium with Lorentz-like dispersion or with dispersion engineered by electromagnetic induced transparency (EIT), is manifested in the splitting of the negative permeability band, the modified (frequency-dependent) filling fractions and dissipation factors. The modified material parameters are strongly linked to the resonant frequencies of the medium, while for an embedding medium exhibiting EIT, also to the strength and detuning of the control field. The robustness of control against the deleterious influence of dissipation associated with the metallic structures as well as the inhomogeneous broadening due to structural imperfections is demonstrated. Studies on plasmonic metamaterials that consist of metallic nanorods arranged in loops and exhibit a collective magnetic response at optical frequencies are presented. Control and switching in this class of plasmonic nanorod metamaterials is shown to be possible, for example, by embedding these arrays in a Raman active liquid like CS$_2$ and utilizing the Inverse Raman Effect.

Electromagnetic momenta and forces in dispersive dielectric media

When the effects of dispersion are included, neither the Abraham nor the Minkowski expression for electromagnetic momentum in a dielectric medium gives the correct recoil momentum for absorbers or emitters of radiation. The total momentum density associated with a field in a dielectric medium has three contributions: (i) the Abraham momentum density of the field, (ii) the momentum density associated with the Abraham force, and (iii) a momentum density arising from the dispersive part of the response of the medium to the field, the latter having a form evidently first derived by Nelson (1991) [8]. All three contributions are required for momentum conservation in the recoil of an absorber or emitter in a dielectric medium. We consider the momentum exchanged and the force on a polarizable particle (e.g., an atom or a small dielectric sphere) in a host dielectric when a pulse of light is incident upon it, including the dispersion of the dielectric medium as well as a dispersive component in the response of the particle to the field. The force can be greatly increased in slow-light dielectric media.

Photons in dispersive dielectrics

The expressions for the electromagnetic components of the polariton modes in a dispersive dielectric medium differ from the mode amplitudes of the electromagnetic field in a nondispersive dielectric. They solve different master equations and are subject to different normalization conditions. We discuss the physics of these differences.

Nanoscale Nonlinear dynamic characterization of the neuron-electrode junction.

Extracellular recordings from neurons using microelectrode and field effect transistor arrays suffer from many problems including low signal to noise ratio, signal attenuation due to counter-ion diffusion from the bulk extracellular medium and a modification of the shape of the cell-generated potentials due to the presence of a highly dispersive dielectric medium in the cell-electrode cleft. Attempts to date to study the neuron-electrode interface have focused on point or area contact linear-equivalent-circuit models. We present here the results obtained from a 'data-true' nonlinear dynamic characterization of the neuron-electrode junction using Volterra-Wiener modeling. For the characterization, NG108-15 cells were cultured on microelectrode arrays and stimulated with broadband Gaussian white noise under voltage clamp mode. A Volterra-Wiener model was then estimated using the input signal and the extracellular signal recorded on the microelectrode. The existence of the second order Wiener kernel confirmed that the recorded extracellular signal had a nonlinear component. The verification of the estimated model was carried out by employing the intracellular action potential as an input to the Volterra-Wiener model and comparing the predicted extracellular response with the corresponding extracellular signal recorded on the microelectrode. We believe that a 'data-true' Volterra-Wiener model of the neuron-electrode junction shall not only facilitate a direct insight into the physicochemical processes taking place at the interface during signal transduction but will also allow one to evolve strategies for engineering the neuron-electrode interface using surface chemical modification of the microelectrodes.

Amplification of the radiation of a bunch of charged particles moving in a waveguide lined with an active dielectric medium

The radiation of a bunch of charged particles moving along the axis of a cylindrical waveguide lined with a resonant dispersive dielectric medium is theoretically studied. Conditions necessary for the amplification of generated waveguide modes are established. It is shown that any selected mode or a group of neighboring modes can be amplified provided that the system parameters are properly chosen. The maximum possible growth increment is independent of the mode number and is determined entirely by the properties of the resonant medium.

Modeling dispersive dielectric media in FDTD: a systematic approach

Two popular and distinct methods to model dispersive dielectric media in finite-difference time domain are the piecewise linear recursive convolution approach and the auxiliary differential equation approach. As they are used to model the same phenomenon and address the same equations, it is reasonable to think there is a close connection between the two. As a result of exploring this connection, we propose a new approach that can be seen as an extension of the two methods and thus, to some extent, serves to unify the two. In addition, the new approach has the advantages of being 1) more systematic-allowing the treatment of different types of dispersive dielectric media in the same manner-and 2) less ad hoc-the so-called recursive accumulators can be identified naturally and automatically.

Radiation pressure and the linear momentum of light in dispersive dielectric media

We derive an exact expression for the radiation pressure of a quasi-monochromatic plane wave incident from the free space onto the flat surface of a semi-infinite dielectric medium. In order to account for the total optical momentum (incident plus reflected) that is transferred to the dielectric, the mechanical momentum acquired by the medium must be added to the rate of flow of the electromagnetic momentum (the so-called Abraham momentum) inside the dielectric. We confirm that the electromagnetic momentum travels with the group velocity of light inside the medium. The photon drag effect in which the photons captured in a semiconductor appear to have the Minkowski momentum is explained by analyzing a model system consisting of a thin absorptive layer embedded in a transparent dielectric.

Radiation of a Charge Moving in a Waveguide with a Resonantly Dispersive Dielectric Layer

The radiation of an ultrarelativistic point charged particle moving along the axis of a cylindrical waveguide containing a layer of resonantly dispersive dielectric medium is studied theoretically. It is shown that, in the case of a sufficiently thin waveguide, the dispersion leads to a significant contraction of the radiation, a decrease in the energy of harmonics, and an increase in the relative contribution due to the first mode as compared to the higher harmonics. These effects are less pronounced in waveguides with relatively large radii; still, they have to be taken into account, especially in determining the frequencies of harmonics. The role of the resonance dispersion is most significant in cases where the dielectric layer thickness is small compared to the waveguide radius.