Group Velocity Of Electromagnetic Waves Research Articles

Dispersion of Exciton Polaritons in Terbium Nitrate Hexahydrate

The dispersion relations of exciton polariton waves in terbium nitrate hexahydrate are determined based on the model of the interaction of electromagnetic waves with resonant electronic states of Tb3+ ions at the 5D4–7F6 transition. Frequencies of unitary polaritons characterized by refractive indices equal to unity are determined. It is shown that the group velocity of electromagnetic waves in the region of unitary polaritons is lower than the speed of light in vacuum by several orders of magnitude. A sharp increase in the efficiency of photoluminescence and Raman scattering is predicted in the case where the excitation radiation frequency approaches the unitary polaritons frequency.

Compensation for Group Velocity of Polychromatic Wave Measurement in Dispersive Medium

The estimation of instantaneous frequency (IF) method is introduced to compensate for the group velocity of electromagnetic wave in dispersive medium. The location of the reflected signal can be obtained by using the time-frequency cross correlation (TFCC), following which it is used to extract the transmitted signal from the total signal acquired. The signal propagated in the dispersive medium is attenuated and distorted by the attenuation characteristics, which depend on the frequency of the medium. By using the IF curve calculated for the transmitted signal, the changed center frequency and time terms can be obtained. The obtained terms are used to compensate for the group velocity error induced by signal distortion and attenuation. Through experiments and simulation, the accuracy of the proposed method is 2% higher than that of the conventional method when the signal propagates over a long distance.

Decameter U-burst Harmonic Pair from a High Loop

The results of the first observations of solar sporadic radio emission within 10 – 70 MHz by the Giant Ukrainian Radio Telescope (GURT) are presented and discussed. Observations in such a wide range of frequencies considerably facilitate the registration of harmonic pairs. The solar U-burst harmonic pair observed on 8 August 2012 is analyzed. The burst key features were determined. Among them, the time delay between the fundamental and harmonic emissions was of special interest. The fundamental emission was delayed for 7 s with respect to the harmonic emission. A model for explaining the occurrence of such a delay is proposed, in which the emission source is located inside a magnetic loop containing plasma of increased density. In this case, the delay appears due to the difference in group velocities of electromagnetic waves at the fundamental and the harmonic frequencies.

Three-dimensional quantum photonic crystals and quantum photonic glasses

The structure and optical properties of quantum-dot photonic crystals (quantytes) were studied. Such crystals have the so-called band gaps, which leads to a strong reflection of electromagnetic waves from the crystal surface. It was shown that in certain spectral regions the refractive index has a negative sign, and the group velocity of electromagnetic waves essentially decreases. The applications of quantytes as optical information recording and rewriting devices, negative refractive optical elements, selective mirrors, narrowband filters, and others were discussed.

Dispersion of electromagnetic waves in a resonant opal photonic crystal filled with Al2O3:Cr3+

We have studied the band structure and group velocity of electromagnetic waves in an opal photonic crystal filled with Al2O3:Cr3+. The results demonstrate that, when a resonance state of the chromium ion falls within the band gap of an unfilled photonic crystal, the group velocity of electromagnetic waves decreases anomalously. We have calculated the dispersion curves and frequency dependences of the group velocity of electromagnetic waves in an opal photonic crystal filled with Al2O3:Cr3+.

Optical properties of photonic crystals filled with iodine vapor

Properties of electromagnetic waves in the photonic crystal with pores filled with iodine vapor are considered. The conditions of the permittivity resonance appearance in the visible region of the spectrum, caused by the electronic transition in iodine molecules, are determined. For the resonant photonic crystal under study, dispersion curves, group velocities of electromagnetic waves, and reflection spectra are calculated for various globule diameters.

Experimental studies of slow wave based on the surface waves in a two-dimensional metamaterials waveguide

In this paper, we study the slow propagation characteristics of surface electromagnetic waves according to theoretical analysis in the MNG (μ-negative)-DPS (double-positive)-MNG waveguide, which is composed of two-dimensional (2D) metamaterials. The dispersion curves of this waveguide vary with circuit parameter (unit capacitors) of MNG metamaterial. At the cutoff frequency of the dispersion curve the group velocity of electromagnetic wave is equal to zero in theory. So we can obtain slow propagation of the surface waves at different cutoff frequencies just by changing the unit capacitor of the MNG metamaterial. Theoretical analysis also shows that the step changes in slow waves are obtained at some fixed frequencies through changing the unit circuit parameters. The experimental results are in good agreement with simulation results.

Group velocity and causality in standard relativistic resistive magnetohydrodynamics

Group velocity of electromagnetic waves in plasmas derived by standard relativistic resistive MHD (resistive RMHD) equations is superluminal. If we assume that the group velocity represents the propagation velocity of a signal, we have to worry about the causality problem. That is, some acausal phenomena may be induced, such that information transportation to the absolute past and spontaneous decrease in the entropy. Here, we tried to find the acausal phenomena using standard resistive RMHD numerical simulations in the suggested situation of the acausal phenomena. The calculation results showed that even in such situations no acausal effect happens. The numerical result with respect to the velocity limit of the information transportation is consistent with a linear theory of wave train propagation. Our results assure that we can use these equations without problems of acausal phenomena.

Frequency-Dependent Rectangular TE30-to-TE10 Mode Converter

Dielectric rod arrays in a metallic waveguide alter the propagation modes and group velocities of electromagnetic waves. We have focused on TE30-to-TE10 mode converters and investigated how their behavior varies with frequency. A mode converter is proposed that passes the TE10 mode at frequencies lower than 2ƒc, and converts the TE30 mode into the TE10 mode for frequencies higher than 3ƒc.

Frequency Range Dependent TE<sub>10</sub> to TE<sub>40</sub> Metallic Waveguide Mode Converter

Dielectric rod arrays in a metallic waveguide alter the propagation modes and group velocities of electromagnetic waves. We focus on TE10-to-TE20 mode converters and investigate the variation in their behavior with frequency. In this investigation, a mode converter is proposed that passes the TE10 mode at frequencies lower than 2fc, and converts the TE10 mode into the TE40 mode for frequencies higher than 2fc, which is achieved by a combination of TE10-TE20 mode converters.

Nonlinear Landau damping of transverse electromagnetic waves in dusty plasmas

High-frequency transverse electromagnetic waves in a collisionless isotropic dusty plasma damp via nonlinear Landau damping. Taking into account the latter we have obtained a generalized set of Zakharov equations with local and nonlocal terms. Then from this coupled set of Zakharov equations a kinetic nonlinear Schrödinger equation with local and nonlocal nonlinearities is derived for special cases. It is shown that the modulation of the amplitude of the electromagnetic waves leads to the modulation instability through the nonlinear Landau damping term. The maximum growth rate is obtained for the special case when the group velocity of electromagnetic waves is close to the dust acoustic velocity.

Possible Abnormal Group Velocity in the Normal Dispersive Anisotropic Media

We introduce a possible method to realize the negative group velocity of electromagnetic wave in the normal dispersive media. Theoretical analysis from the k-surface of the proposed normal dispersive uniaxial media reveals that the group velocity can be negative if the loss of the media is taken into account. Since the proposed normal dispersive media can be constructed in the GHz frequency by metamaterial, our result may provide an alternative way to the investigation of the abnormal group velocity.

Simulations of defect-free coupled-resonator optical waveguides constructed in 12-fold quasiperiodic photonic crystals

In this paper we propose a defect free coupled-resonator optical waveguide (CROW) that is constructed based on the intrinsic localized modes in a 12-fold quasiperiodic photonic crystal (QPC). Different from the usual CROW created by introducing a serial of point defects in a periodic photonic crystal, the special CROW is fabricated by modifying the 12-fold QPC without destroying its basic cells. Our simulation results indicate that the guiding efficiency of the CROW is high. Furthermore, compared with the CROW constructed in a periodic photonic crystal, the maximal value of the group velocity of electromagnetic waves propagating in this kind of CROW can be greatly reduced.

Waveguide modes in coupled-resonator optical waveguides

Coupling between cavities within coupled-resonator optical waveguides (CROWs) affects transmission properties. Our results show that, in addition to the number of the waveguide modes, the group velocity of electromagnetic waves transmitted in the CROWs can be controlled by changing the stiffness of coupling between cavities. This is significant for the applications.

Coupling of the TE and TM modes of electromagnetic waves in two-dimensional photonic crystals with surface defects of liquid crystals.

We theoretically demonstrate the coupling of the TE and TM modes of electromagnetic waves in two-dimensional photonic crystals with surface defects of liquid crystals. Due to anisotropies of liquid crystals, the TE and TM modes cannot be classified generally in the surface defects, which causes the coupling of the TE and TM modes. The coupling of the TE and TM modes occurs strongly at frequencies at which group velocities of electromagnetic waves become zero, especially at surface defect modes. Possibility of the sharp tunability and the switching of the transmittance in this system has been demonstrated theoretically by the control of directors of liquid crystals by applied electric field due to their anisotropy.

The group velocity of electromagnetic waves diffracted by a small aperture

Diffraction of electromagnetic waves by an aperture in an infinite opaque screen is approached using an integral expression characterized by the spatial Fourier transform at the aperture. The group velocity of the field propagated from the aperture assumes a continuous distribution of values corresponding to the distribution in transverse wavenumber. The gravitational Doppler shift is computed for an aperture that is small compared to a wavelength. It is found that the integral expression can be evaluated analytically, leading to a distribution of Doppler shifts; the minimum Doppler shift is on the order of one part in 10 15. Every additional order of magnitude increase in the Doppler shift results in a decrease in amplitude by two orders of magnitude.

Frequency-domain detection of superluminal group velocity in a distributed Bragg reflector

Using a free-space configuration and a frequency-domain detection setup, group velocities of electromagnetic waves in a distributed Bragg reflector are investigated. Experimental data indicate that, near the regions of minimal transmission in our configuration, the group velocity is 2.1 times faster than the speed of light in vacuum. A transmission model based on diagonalization of the transfer matrix is used to compare the experimental data and the theoretical calculations, and good agreement is obtained. An overview of the experimental uncertainties and their effects on the measured quantities is provided.

Causality in QED with boundaries

A two-loop effect, uncovered by Scharnhost, causes both the phase and the group velocities of electromagnetic waves with ω ⪡ m e to exceed c, when the wave is travelling between parallel conducting plates. We begin an analysis of the structure of the one-loop four-point function in flat space (this operator is used in the construction of the two-loop vacuum polarization function) that ensures the non-trivial dependence on frequency of both the effective action and the refractive index. Including corrections due to boundaries, this operator leads to the vanishing asymptotic behaviour of the vacuum polarization function which, contrary to the suggestion of Scharnhost and Barton, avoids the propagation of non-causal signals.

The direction of the group velocity of electromagnetic waves in a multicomponent magneto-active plasma in the frequency range 0 < ω → ∞

The results of investigating the direction of the group velocity vector ∂ω/∂K̄ of all the branches of the electromagnetic waves existing in a cold magnetoactive plasma are given. Calculations are performed for the entire frequency range 0≤ ω ≤ ω H , ω 0; ω 0, ω H ≤ ω → ∞( ω 0 and ω H are the Langmuir and gyrofrequencies of electrons, respectively) in the case when plasma contains three sorts of ion. Some important properties of the direction of ∂ω/∂K̄ are revealed. It is shown, in particular, that in the vicinity of the ion-ion hybrid frequencies one of the branches of waves is well guided by the magnetic field H ̄ 0 and that at the crossover frequencies the direction of this branch of waves is close to the direction of H ̄ 0 .

Radiation pressure and ‘aether drag’ in a dispersive medium

ARNAUD1 has pointed out that there should be no transverse ‘aether drag’ in an artificial dielectric consisting of parallel plane conducting elements, where the product of the phase and group velocities of electromagnetic waves should be equal to the square of the velocity of light in vacuo. This agreed with the formula derived by Player2 and Rogers3, who for some important examples of aether drag showed that the Fresnel drag coefficient (1–1/n2), where n is the refractive index, should more precisely be replaced by (1 – 1/nφng), where nφ and ng are respectively the (phase, or normal) refractive index and the ‘group’ refractive index.