Resonant Absorption Of Electromagnetic Waves Research Articles

Resonant absorption of electromagnetic waves by an induced inhomogeneity in a liquid metamaterial

In this study, we consider the scattering of a plane electromagnetic wave on a cylindrically inhomogeneous distribution of meta-atoms in a liquid metamaterial. The distribution inhomogeneity appears naturally as a result of the application of an electric potential to an electrode immersed in the liquid metamaterial, which leads to the appearance of inhomogeneity in the effective permittivity of such a medium. Consequently, in the considered type of metamaterial, the concentration-dependent effective permittivity can become negative in some region of space. In the vicinity of the interface between positive and negative permittivity, the behavior of the electromagnetic wave becomes singular, giving rise to effects such as resonant absorption, resonant scattering, and shielding of the central region. These effects can be controlled in real time by changing the applied electric potential and thus rearranging the liquid metamaterial.

Large-area mid-infrared broadband absorbers based on spiral ITO resulting from the combination of two different broadening absorption methods

A large-area mid-infrared broadband absorber is proposed in this paper. The absorber is a spiral ITO structure grown on a hexagonal lattice arrangement of silicon nanopillars by using a glancing angle deposition method. The experimental results show that when the heights of the silicon nanopillars are 1.7 µm and the number of rotation depositions is n = 5, that is, the rotation angle is 150 degrees, the absorber absorbs more than 81% of electromagnetic waves in the 2.5-6 µm spectral range. In the atmospheric window of 3-5 µm, the integral absorption reaches 96%. The experimental results also show that the absorbing ability of the ITO structure in the mid-infrared atmospheric window is significantly stronger than that of the structure composed of silver under the same preparation conditions. The main reasons for the broadband absorption are that the spiral ITO structure has resonant absorption of electromagnetic waves with different wavelengths in the empty cavity regions with different sizes, and ITO has longer penetration depths than noble metals in the mid-infrared band, which brings about stronger broadband absorption. The combination of the two leads to a broadening of the total absorption spectrum. The higher heights of the silicon nanopillars enhance absorption further. Additionally, the loose spiral ITO distributions indicate lower mean plasma concentration and then increase penetration depths further, resulting in stronger light absorption. Such a large-area mid-infrared absorption structure with a simple preparation method has potential applications in mid-infrared cloaking and sensing.

Collisional and resonance absorption of electromagnetic waves in a weakly collisional, inhomogeneous magnetoplasma slab

Absorbance of normally incident electromagnetic wave on a cold, weakly collisional, and inhomogeneous magnetoplasma slab is investigated. The plasma density is Budden-like sinusoidal profile, where the inhomogeniety is treated as a multilayered system of homogeneous sub-cells within the transfer matrix technique. For incident wave frequencies much above the ion cyclotron frequency, only right hand circularly polarized waves are relevant for wave propagation parallel to a static magnetic field. Calculations are performed in normalized parameters, that make the results suitable for many applications including atmospheric and laboratory plasmas. The presence of the dc-magnetic field leads to the formation of two absorption bands explained by plasma collisional dissipation and electron cyclotron resonance in the low frequency branch of the $R$-wave below the electron cyclotron frequency. The transmittance shows the emergence of the low frequency electron cyclotron wave, which becomes a Whistler mode at very low frequency. More detailed discussion on the effect of plasma collisionality, inhomogeneity, and dc-magnetic field on the propagation characteristics is given at the relevant place within the body of the manuscript.

Resonant absorption of electromagnetic waves in transition anisotropic media.

We study the mode conversion and resonant absorption phenomena occurring in a slab of a stratified anisotropic medium, optical axes of which are tilted with respect to the direction of inhomogeneity, using the invariant imbedding theory of wave propagation. When the tilt angle is zero, mode conversion occurs if the longitudinal component of the permittivity tensor, which is the one in the direction of inhomogeneity in the non-tilted case, varies from positive to negative values within the medium, while the transverse component plays no role. When the tilt angle is nonzero, the wave transmission and absorption show an asymmetry under the sign change of the incident angle in a range of the tilt angle, while the reflection is always symmetric. We calculate the reflectance, the transmittance and the absorptance for several configurations of the permittivity tensor and find that resonant absorption is greatly enhanced when the medium from the incident surface to the resonance region is hyperbolic than when it is elliptic. For certain configurations, the transmittance and absorptance curves display sharp peaks at some incident angles determined by the tilt angle.

Spectroscopic ellipsometric properties of annealed Mn1.95Co0.77Ni0.28O4 thin films.

Mn-Co-Ni-O thin films have important application values, but their spectroscopic ellipsometric properties undergoing post-annealing are still short of studies. In this Letter, the visible near-infrared ellipsometric data of post-annealed Mn1.95Co0.77Ni0.28O4 thin films were fitted by double Lorenz, Drude, and effective medium approximation models. We found that the Lorenz model can describe the small polaron oscillation, and the Drude model can excellently fit the conductivity produced by small polaron hopping. We found that a large number of carriers hopping between bound states under certain voltage generates a unidirectional flow of quasi-free carriers, which can bring about the same macroscopic properties as free carriers in extended state, and the calculated effective mass of quasi-free carriers is about 150m0 (m0 is the effective mass of electrons). We also found that it is mainly Lorentz oscillators and the quasi-free carriers that produce the resonance absorption of electromagnetic waves in the visible near-infrared waveband, and both have electron absorption of lights. These results will perfect the small polaron hopping theory for Mn-Co-Ni-O thin films.

Can nanoparticles be useful for antiviral therapy?

In this paper, optical properties of the system consisting of mesoparticles (small dielectric particles) and nanoparticles (quantum dots) of various shapes have been considered. This system can be characterized by resonant absorption of electromagnetic waves and used for developing the new approach to antiviral therapy.

Semi-analytical model of laser resonance absorption in plasmas with a parabolic density profile

Analytical expressions for mode conversion and resonance absorption of electromagnetic waves in inhomogeneous, unmagnetized plasmas are required for laboratory and simulation studies. Although most of the analyses of this problem have concentrated on the linear plasma density profile, there are a few research works that deal with different plasma density profiles including the parabolic profile. Almost none of them could give clear analytical formulae for the electric and magnetic components of the electromagnetic field propagating through inhomogeneous plasmas. In this paper, we have considered the resonant absorption of laser light near the critical density of plasmas with parabolic electron density profiles followed by a uniform over-dense region and have obtained expressions for the electric and magnetic vectors of laser light propagating through the plasma. An estimation of the fractional absorption of laser energy has also been carried out. It has been shown that, in contrast to the linear density profile, the energy absorption depends explicitly on the value of collision frequency as well as on a new parameter, N, called the over-dense density order.

Improved planar radio frequency inductively coupled plasma configuration in plasma immersion ion implantation

Plasmas with higher density and better uniformity are produced using an improved planar radio frequency (rf) inductively coupled plasma configuration in plasma immersion ion implantation (PIII). An axial magnetic field is produced by external electromagnetic coils outside the discharge chamber. The rf power can be effectively absorbed by the plasma in the vicinity of the electron gyrofrequency due to the enhanced resonant absorption of electromagnetic waves in the whistler wave range, which can propagate nearly along the magnetic field lines thus greatly increases the plasma density. The plasma is confined by a longitudinal multipolar cusp magnetic field made of permanent magnets outside the process chamber. It can improve the plasma uniformity without significantly affecting the ion density. The plasma density can be increased from 3×109 to 1×1010 cm−3 employing an axial magnetic field of several Gauss at 1000 W rf power and 5×10−4 Torr gas pressure. The nonuniformity of the plasma density is less than 10% and can be achieved in a process chamber with a diameter of 600 mm. Since the plasma generation and process chambers are separate, plasma extinction due to the plasma sheath touching the chamber wall in high-energy PIII can be avoided. Hence, low-pressure, high-energy, and high-uniformity ion implantation can be accomplished using this setup.

Dynamical conductivity of a two-dimensional electron gas under an intense terahertz radiation

By using a kinetic description method, we calculate the conductivity of a two-dimensional electron gas under an intense terahertz radiation. Our result includes all contributions from electron–photon side-bands and in lowest order of electron impurity scattering. Resonant absorption of electromagnetic waves by the coupled electron–photon system is discussed.

The anomalous resonance absorption of electromagnetic waves as a phenomenon of radiative damping

The well-known anomalous absorption of transverse electromagnetic waves near the resonance point of a plasma surface is described as a phenomenon of radiative damping of waves. Reflections from a sharp plasma surface and from smoothly inhomogenous plasma are considered separately. It is shown that during the reflection ofE-waves from the surface of a smoothly bounded inhomogeneous plasma, radiative damping occurs in the reflecting point as a result of longitudinal plasma waves emission and it is also shown that anomalous absorption of electromagnetic waves in the long-wavelength limit is significant as well as in the short wavelength.

Ion Heating by Resonant Absorption of Electromagnetic Waves in Multi-Ionic Plasmas: A Process for the Formation of Ion Conics.

Conical distribution of both light and heavy ions are commonly observed in the magnetospheric plasma at various altitudes above the auroral regions and in the cusp/cleft region. The occurrence of these conics is shown to be well correlated with the presence of low frequency mannetosonic waves having frequencies close to the gyrofrequency of the heated ions, Dynamical spectra recorded onboard the AUREOL 3 satellite during the simultaneous occurrence of these waves and the generation of H + conics have shown that, in such a case, resonant wave absorption at the gyrofrequency of the protons is likely to occur. These phenomena are due to the propagation, reflection and subsequent conversion of the magnetosonic waves throughout the inhomogeneous magnetospheric plasma. Theory allows to determine the energy budget of the resonant absorption and to describe some features of the observed spectra. Following similar ideas it is also possible to build up a theoretical scenario aiming at explaining the transverse heating of O + ions and the formation of oxygen conics. As described in the experimental literature, this likely occurs far above the topside ionosphere and thus at higher altitudes than covered by the AUREOL 3 spacecraft

Nonlinear mode conversion with chaotic soliton generation at plasma resonance

The resonant absorption of electromagnetic waves near the critical density in inhomogeneous plasmas is studied. A driven nonlinear Schr\odinger equation for the mode-converted oscillations is derived by multiple-scaling techniques. The model is simulated numerically. The generic transition from a stationary to a time-dependent solution is investigated. Depending on the parameters, a time-chaotic behavior is found. By a nonlinear analysis, based on the inverse scattering transform, solitons of a corresponding integrable equation are identified as the dominant coherent structures of the chaotic dynamics. Finally, a map is presented which predicts chaotic soliton generation and emission at the critical density. Its qualitative behavior, concerning the bifurcation points, is in excellent agreement with the numerical simulations.

Induced resonant absorption of electromagnetic waves by a microparticle

Light absorption by a microparticle in the presence of an atom with the optical transition frequency being resonant with the light frequency is theoretically investigated. The possibility of cascade energy transfer from light to an atom and then to a microparticle is found. The efficiency of cascade-type energy transfer to the microparticle essentially depends on the irradiation condition and the distance between the microparticle and the atom.

Parametric instabilities in resonant absorption

The resonant absorption of electromagnetic waves in an inhomogeneous plasma is studied using a 2-D particle code. For the studied flux (Φ>8×1014 W/cm2), it is shown that it is impossible to separate resonant absorption from parametric instabilities. Effects of these instabilities on the absorption of incident energy and heating of particles are considered.

Numerical Analysis on Linear Resonant Absorption in Plasmas

Theoretical analyses on the linear resonant absorption of electromagnetic waves in inhomogeneous plasmas given by various authors are re-examined by numerical computation. A set of linearized equations in which collisional and thermal effects of the electrons are included is solved numerically for a wide range of plasma parameters by developing an implicit difference scheme with extremely small numerical errors. We are successful to decrease electron temperatures as low as 200 K. It is concluded that the Denisov's factor \((\upsilon_{\text{t}}/\sqrt{2}{\omega}L)^{2/3}\) with a numerical correction can be used to calculate the peak electrostatic fields at the resonant surface, if his factor is larger than 20 times the collisional factor ν/ω. Here, L is the characteristic length of the density gradient and other notations are standard. An empirical formula to calculate the peak field in the presence of both collisional and thermal effects is proposed.

Pseudosolitons formation in resonant absorption of electromagnetic waves

The resonant absorption of electromagnetic waves in an inhomogeneous plasma is studied at low intensity. Both fluid and particle models confirm the formation of solitons predicted by the Zakharov equations. The effects on the absorption coefficient and hot electron production are considered.

Efficiency of resonant absorption of electromagnetic waves in an inhomogeneous plasma

The resonant absorption of electromagnetic waves in an inhomogeneous plasma is studied for values of the resonant plasma wave field such that the ponderomotive effects modify wave propagation. The stationary solutions are obtained and found unstable with low dissipation in most cases. The absorption coefficient is then time dependent. Density cavities are emitted at the resonance and they can induce large frequency shifts for the reflected light.

Resonant absorption of electromagnetic waves in a randomly inhomogeneous collisionless plasma

Resonant absorption of electromagnetic waves in a randomly inhomogeneous collisionless plasma

Anomalous Dielectric Dispersion in Glasses at Low Temperatures

We have found a strong temperature dependence in the dielectric constant of three different glasses below 5 K, which we ascribe to the low-energy excitations of the amorphous state. From our data we can determine the electrical dipole moment associated with these excitations, which gives rise to resonant absorption of electromagnetic waves. The corresponding absorption coefficient is expected to saturate at electromagnetic intensities above a few milliwatts per square centimeter.

Resonant absorption of electromagnetic waves in a non-uniformly magnetized plasma

The propagation and collisionless absorption of electromagnetic waves propagating in non-uniformly magnetized plasmas with regions of cyclotron resonance are computed. The particle dynamics associated with motion in a non-uniform magnetic field near cyclotron resonance is considered explicitly. Above a critical plasma density complete wave absorption is predicted. At high plasma densities particles with high velocities along the field lines are heated preferentially whereas at lower densities the slower particles gain more energy per particle from the wave. At high densities the wave is attenuated by the high energy tail of the velocity distribution; this dissipation is shown to be consistent with the uniform field results of Stix. The lack of heating observed in Princeton ioncyclotron wave absorption experiments is resolved by considering the wave launching efficiency.