Absorption of electromagnetic radiation by semimetal electrons

The coefficient of electromagnetic radiation absorption by bismuth in a quantizing magnetic field is calculated by perturbation theory methods. An expression is obtained for the resonance frequencies. It is shown that the electron dispersion law not being quadratic results in spin splitting of the resonance peaks.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 62–67, December, 1985.In conclusion, the author is grateful to A. D. Margulis for formulating the problem and constant guidance of the research.     

A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.T. Manabe was with the Institute for Telecommunication Sciences, NTIA-DoC, on leave from the Radio Research Laboratory, Ministry of Posts and Telecommunications, Koganei, Tokyo 184. He is now with ATR Optical and Radio Communications Research Laboratories, Seika-cho, Soraku-gun, Kyoto 619-02, Japan.     

Absorption of electromagnetic radiation by electrons of a nanosphere

The electrodynamic response of an electron gas on the surface of a nanosphere is investigated. An analytical relationship for the absorption of electromagnetic radiation by the nanosphere is derived. It is demonstrated that the absorption curve at low temperatures has two resonance peaks. The shape, position, and intensity of the peaks are examined. The dependence of the absorption on the radiation frequency exhibits kinks associated with the degeneracy of the electron gas. The number and position of the kinks and the absorption jumps at these kinks are analyzed. Consideration is given to the cases of an isolated sphere and a sphere exchanging electrons with a reservoir.     

Absorption of electromagnetic radiation by an inhomogeneous spherical particle

The cross section of absorption of electromagnetic radiation by an inhomogeneous spherical particle is calculated. The general case of an arbitrary value of the ratio of the particle radius to the radius of the dielectric core is considered. The condition of diffuse reflection of electrons from the inner and outer surfaces of the metal layer of the particle is taken as the boundary condition of the problem. The limiting cases are considered and the results obtained are discussed.     

Absorption of electromagnetic radiation by a cylindrical metal particle

The cross section of the absorption of electromagnetic radiation by a cylindrical metal particle is calculated. The calculation is performed in the low-frequency limit, in which the contribution of eddy currents to the absorption dominates, and for comparatively small particles (with radii of ≈10 nm), which allows us to neglect the skin effect. The case when the mean free path of electrons in the metal bulk substantially exceeds the radius of the cylindrical particle is considered in detail. The specific absorption cross sections for spherical and cylindrical particles are compared.     

Absorption of solar radiation by charged water droplets

We consider the absorption of solar radiation by charge accumulated on the surface of an otherwise neutral water droplet. We estimate the order of magnitude of the additional contribution from the surface charges to the photoabsorption cross-section. The approximate location and strength of major spectral lines is indicated. This spectral information requires determination of the quantum mechanical energy levels and wave functions of the absorbing system. An approximate calculation is carried out using a simple model for electrons on the surface of the droplet. The implications for atmospheric applications are considered.     

AC magnetic susceptibility at medium frequencies suggests a paramagnetic behavior of pure water

The AC magnetic susceptibility of water is studied in the frequency range of 1 kHz-1 MHz at a low magnetic field. The results show a paramagnetic behavior between 500 kHz and 1 MHz for samples at 37 °C and 25 °C, which is surprising considering that water is believed to be diamagnetic. AC magnetic susceptibilities for ice and different salt solutions were investigated as well: in such cases the susceptibility is always negative and therefore, such samples remain diamagnetic.     

Absorption of electromagnetic radiation by systems with a noncollinear magnetization distribution

The high-frequency absorption of electromagnetic radiation in systems with a noncollinear spatial magnetization distribution has been calculated. A medium with a helicoidal magnetic structure and a superlattice whose period contains two layers with noncollinear magnetizations are considered. An additional absorption peak related to the electron transitions from one spin subband to another under the action of a variable linearly polarized electric field is shown to appear in such systems at frequencies near the spin splitting of the conduction band.     

Absorption and defocusing of electromagnetic radiation by a Schwarzschild black hole

A comparison of electromagnetic radiation absorbed by a black hole and that emitted at infinity is made for selected circular orbits of a charged particle in a Schwarzschild geometry. Radiation intensity and beaming processes for geodesic as well as ultra-relativistic unbound orbits are compared and contrasted with the special relativistic results of classical electrodynamics.     

Absorption of resonant electromagnetic radiation in electron-atom collisions

Nonrelativistic quantum theory is used to study the possibility of amplification of electromagnetic radiation in forced braking scattering of an electron beam on atoms. The interaction of the atom with the electromagnetic field is considered in the resonant approximation. Cases of large and small detuning from resonance are considered. It is shown that for any orientation of the electron beam relative to the field polarization vector, absorption of radiation occurs, with the major contribution being produced by atomic electrons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 79–84, April, 1986.The authors are indebted to M. F. Fedorov and S. I. Yakovlenko for their valuable discussion and advice.     

Absorption of electromagnetic radiation by a bimetallic cylindrical particle of finite length

The absorption cross section of electromagnetic radiation is calculated for a bimetallic cylindrical particle of finite length. A general case is considered, where the ratio of the radius of the particle core to the particle radius and the ratio of the radius of the particle to its length can take arbitrary values. The conditions of diffuse reflection of electrons from the internal and external surfaces of the metal shell of the particle and from its faces are used as the boundary conditions of the problem. The effect of the ratio of the radius of the core of a bimetallic cylindrical particle to the particle radius and the ratio of the radius of the particle to its length on the electromagnetic properties of the particle is analyzed.     

Absorption properties of the near-infrared water vapor bands

Spectral absorptances and equivalent widths of the near-infrared water vapor bands at 0.7, 0.8, 0.9, 1.1, 1.4 and 1.9 μm were measured for several sample parameters. Band strengths were determined for these six bands by comparing the measured equivalent widths with theoretical values obtained from line-by-line calculations. Absorptions estimated from empirical equations of Howard, Burch and Williams agreed reasonably well with our results for the 1.4- and 1.9-μm bands, but discrepancies were found for the 0.9- and 1.1-μm bands. Absorptions of the 0.7- and 0.8-μm bands measured by Fowle agreed with our results within 10% or less. Absorption functions are given for the specified six bands.     

Directional radiation pattern of luminescent photonic crystals at frequencies near the second photonic stop band

The possibility of the directional enhancement of luminescence at frequencies near the edge of the second photonic bandgap of opal-type photonic crystals has been demonstrated both theoretically and experimentally. The directional patterns of radiation have been simulated by calculating the angular dependences of the density of optical states. The calculation results are compared to the experimental data obtained for the thin-film opals with terbium-containing complexes. Good agreement is achieved after the strong smoothing of the calculated curves; this smoothing is necessary because of the imperfection of the structure of actual samples.     

Absorption of electromagnetic radiation in systems with orientational interactions

Absorption of electromagnetic radiation in ordered ferroelectric and antiferro-electric systems in external electrical fields has been investigated by means of Monte Carlo method. The dependences of the areas of the hysteresis curves on the frequency of the field have been calculated. At the resonance frequency, there is a maximum of the area of the hysteresis curve; the position of this maximum depends weakly on the temperature and the constant of intra- and interchain inte-ractions, and its height increases with decreasing temperature and increasing the interaction energy between molecules.     

Characterization of coherent THz radiation bursting regime at Elettra

Coherent Terahertz radiation has been observed in the third generation synchrotron light source Elettra. The radiation emitted in bursts shows a wavelength distribution shorter than the nominal electronic bunch length suggesting that the microscopic emission mechanism is due to the beam instabilities. In this paper we discuss the effects of the instabilities and present preliminary spectroscopic measurements.     

Long-range surface plasmon polaritons at THz frequencies in thin semiconductor layers

We present a theoretical investigation of THz long-range surface plasmon polaritons propagating on thin layers of InSb.The metallic behavior of doped semiconductors at THz frequencies allows the excitation of surface plasmon polaritons with propagation and confinement lengths that can be actively controlled.This control is achieved by acting on the free carrier density,which can be realized by changing the temperature of InSb.     

On the absorption of electromagnetic radiation near a metal surface

We present a discussion on the absorptance of electromagnetic radiation per unit length in the surface region of a free electron like metal. We wish particularly to comment on recent work by Feibelman, Kliewer, Forstmann and Stenscke, who all considered different approximations of the jellium model. We are using a unified treatment from which the results in their models can easily be obtained. Our results confirm the general conclusions by Kliewer about a strong coupling to the electron-hole excitations which lead to a locally negative absorptance. In the model considered by Feibelman there is no such coupling to electron-hole excitations and he obtains the classical results for the absorptance. Forstmann and Stenschke have recently applied a hydrodynamical approach which gives results in disagreement with Kliewer's theory as well as with our own results, and we make some comments about their approach.     

Absorption of electromagnetic waves by graphene

The power of the circularly polarized electromagnetic wave absorbed by graphene is calculated using the Boltzmann kinetic equation written in the relaxation approximation and the numerical Monte Carlo simulation. It is shown that in the limit of large radiation amplitudes the power absorbed by graphene is directly proportional to the amplitude irrespective of the electron gas statistics.