Emission Of Electromagnetic Radiation Research Articles

Skin depth at microwave frequencies of sea foam layers with vertical profile of void fraction

To develop a foam emissivity model, we started a systematic investigation of sea foam properties at microwave frequencies from 1 to 37 GHz. We first examined various permittivity formulae to find the most suitable one for obtaining the dielectric constant of sea foam. This paper presents an investigation of the skin depth of vertically structured foam layers for the first time. Various void fraction profiles representing variations of foam properties within the foam thickness are examined. The skin depth of foam layer thicknesses from 0.2 cm to 10 cm is obtained. The dependence of foam skin depth on frequency and foam layer thickness is investigated and compared to seawater skin depth. It was found that for exponential void fraction profile ranging from 99% at the air‐foam interface to 1% at the foam‐seawater boundary, the foam skin depth varies from 0.17 cm to no more than 7 cm. Possible variations of the foam skin depth due to permittivity formula choice, seawater temperature and salinity, and shape of void fraction profile, as well as its upper and lower limits, are presented. Analyses of the results help explain the sensitivity of microwave frequencies to foam layer thicknesses, infer the formation of the emissivity signal and its variations from foam‐covered surfaces, infer implications for the passive remote sensing of whitecaps, discuss modeling approaches for vertically structured foam layers, and infer qualitatively the relative contributions of different foam structures to the absorption and emission of electromagnetic radiation. These findings give conceptual understanding of foam emissivity.

Heat recovery mechanism in the excitation of radiative polaritons by broadband infrared radiation in thin oxide films

This work probes radiative polaritons in thin oxide layers as a mean to capture and absorb broadband infrared radiation and transform it into heat. A heat recovery mechanism, based on the Seebeck effect, is used as the tool of the investigation. Heat production challenges the current understanding which views the excitation of radiative polaritons as only accompanied by the emission of electromagnetic radiation. The heat recovery mechanism presented here can inspire the design of infrared energy harvesting devices, similar to photovoltaic cells, and other devices to convert energy from a wide range of the electromagnetic radiation spectrum using thermoelectric power generators.

Coherent Cherenkov Radiation from Cosmic-Ray-Induced Air Showers

Very energetic cosmic rays entering the atmosphere of Earth will create a plasma cloud moving with almost the speed of light. The magnetic field of Earth induces an electric current in this cloud which is responsible for the emission of coherent electromagnetic radiation. We propose to search for a new effect: Because of the index of refraction of air, this radiation is collimated in a Cherenkov cone. To express the difference from usual Cherenkov radiation, i.e., the emission from a fast-moving electric charge, we call this magnetically induced Cherenkov radiation. We indicate its signature and possible experimental verification.

The long journey to the laser and its rapid development after 1960

The laser, a fascinating new light source with numerous applications in our daily life was first realized some 50 years ago. The principle was initiated in 1916 when Einstein introduced a new concept of radiation-matter-interaction known today as stimulated emission of electromagnetic radiation. It took nearly 40 years before a first practical device based on stimulated emission – the maser – was realized for microwaves in 1954. In 1960, the first laser was operated in the visible. This historical note reports on the way to the laser with its climax in 1960. The subsequent explosive development of new lasers and of fundamental applications is shortly reviewed in the second part of the paper.

Subterahertz Emission at Strong REB-Plasma Interaction in Multimirror Trap GOL-3

Investigation results for electromagnetic radiation emission induced by strong Langmuir turbulence driven by a microsecond relativistic electron beam are presented. The radiation is associated with a plasmon-plasmon merging process, which generates photons at a double plasma frequency in the range of few hundreds GHz. An original radiometric system for radiation spectrum and power measurements is described.

An Integrated Study of the Dynamics of Electromagnetic and Acoustic Regimes During Failure of Complex Macrosystems Using Rock Blocks

The development of the failure process in complex macrosystems using large rock samples subjected to biaxial compression has been studied by means of electromagnetic radiation (EMR) and acoustic emission (AE). In order to increase the stage of macrofailure development, a special procedure of rock loading was used to reveal regularities of nucleation and evolution of electromagnetic and acoustic structures. The synchronised measurements of EMR and AE allowed the control of the stress–strain state in the rocks and the structural developments of fracturing. Non-homogeneous distribution of the rock spatial crystalline structure subject to load leads to a mosaic distribution of EMR and AE characteristics. As a result, the crack scale effect may be observed in the EMR and AE structure behaviours. The EMR and AE following the failure at different levels behave differently according to the difference in the scale and type of cracks. Intense high-frequency EMR pulses were recorded during the initial stage of microcrack generation occurring prior to major failure of material. This was not the case for AE. The nucleation and development of the macroscopic progressive failure evolution caused an alternation in energetic and frequencial properties of electromagnetic and acoustic events. It has been detected that the tensile cracks were more efficient than shear cracks in capacity of EMR generation. The analysis of self potentials allowed reaching the maximum of registered anomalous variations in the stage of microcracking interaction. This stage showed an increase in the EMR activity, which implies the nucleation of microcracks in various regions of rock interfaces. The gradual accumulation of these defects led to weakening some parts of the rock along with a disintegration of electric anomalies, increase of AE and a significant fluctuation in the rate of EMR. When crack concentration attains its critical value, which results in the formation of dangerous macroscopic failure of higher level, AE shows an intense activity as well as an EMR lower frequency. The hierarchical development of rock failure using the ratio of the average crack size and the mean distance between cracks as a statistical concentration criterion is used to control the boundary of the transition from small dispersed cracks accumulation to gradual crack merger and the formation of the main macrofailure. These results could be transferred into larger scale levels to forecast dynamic events in the earth crust.

Multichannel Radiometric System for Registering Submillimeter-Wave Radiation at Beam-Plasma Interaction

We describe a 4-channel radiometric system developed for registering pulses of submillimeter-wave radiation in the frequency band 210-530 GHz. The system employs a quasi-optical scheme with polarization demultiplexed channels, wherein subsequent frequency filtering and spectral signal detection are provided by quasi-optical bandpass filters and high-speed Schottky detectors respectively. The system has frequency resolution of the channels ~30-50 GHz and response time better than 2 ns and destined for registering emission of electromagnetic radiation in the vicinity of a double plasma frequency, which is produced at turbulent heating of dense plasma in the multimirror magnetic trap GOL-3 by a powerful relativistic electron beam of 10 microsecond duration.

Electromagnetic radiation during plastic deformation under unrestricted quasi-static compression in metals and alloys

Abstract Intermittent electromagnetic radiation (EMR) emissions from metals and alloys during deformation under unrestricted quasi-static compression are reported in this paper. The end surface conditions of the compressing platens, whether lubricated or unlubricated, influence the EMR emission characteristics. The EMR emissions under compression show shape anisotropy. The first EMR emission invariably occurs near the yield. The EMR emission characteristics are also influenced by the crystal structure. During axial compression, dead metal zones formed on the top and bottom portions of the specimens possibly generate a climbing motion of edge dislocations in the radially outward mid-regions. During the climbing motion, these edge dislocations form accelerated electric line dipoles and emit electromagnetic radiation. These EMR emissions can be used to evaluate the degree of damage in metallic components under compression.

Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields

In addition to producing loud gravitational waves, the dynamics of a binary black hole system could induce emission of electromagnetic radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.

Bremsstrahlung from relativistic heavy ions in matter

The emission of electromagnetic radiation by relativistic bare heavy ions penetrating ordinary matter is investigated. Our main aim is to determine the bremsstrahlung which we define as the radiation emitted when the projectile does not break up. It pertains to collisions without nuclear contact ('ultraperipheral collisions'). Requirement of coherent action of the nucleons in order to keep the penetrating projectile intact limits bremsstrahlung to relatively soft photons. The spectrum shows a resonance structure with peak position near 2{gamma} times the position of the giant dipole resonance, that is, near 25{gamma} MeV for a lead ion ({gamma}{identical_to}E/Mc{sup 2} is the Lorentz factor of the projectile of energy E and mass M). The maximum exceeds the bremsstrahlung from a hypothetical structureless, pointlike particle of the same charge and mass as the incoming nucleus, but rapid depletion follows on the high-energy side of the peak. As a result of its relative softness, bremsstrahlung never dominates the energy-loss process for heavy ions. As to the emission of electromagnetic radiation in collisions with nuclear break-up, it appears modest when pertaining to incoherent action of the projectile nucleons in noncontact collisions. In collisions with nuclear contact, though, substantial radiation is emitted. It overshoots the bremsstrahlung. However, more » despite the violence of contact events, the associated photon emission only exceeds the radiation from a hypothetical structureless pointlike nucleus [emitted energy per unit photon-energy interval essentially constant up to ({gamma}-1)Mc{sup 2}] at relatively low photon energies (for lead roughly below 0.2{gamma} GeV, a limit which is about an order of magnitude above the position of the bremsstrahlung peak). Results are presented for bare lead ions penetrating a solid lead target at energies of 158 GeV/n ({gamma}=170) and beyond. « less

Effect of Peierls’ stress on the electromagnetic radiation during yielding of metals

This paper presents a theoretical model to analyze the effect of Peierls’ stress on the electromagnetic radiation (EMR) during the yielding of metals. The theoretical predictions are analyzed on the basis of experimental results in bcc 0.15% carbon steel. The computed results show that the maximum amplitude V max of the voltage due to radiation and induction electric fields during the yield is inversely proportional to the exponential of the effective Peierls’ stress and bears a relation of the form, V max = k 1exp(− k 2 σ Pe), where k 1 and k 2 depend upon the instrumentation parameters as well as the metal properties. This leads to a new technique for the evaluation of effective Peierls’ stress in metals. Finally, the present paper also brings out some clarity in the previous model (without Peierls’ stress) of the authors, regarding the directions of electric dipole moment and its time derivatives, which are formed by the edge dislocations during plastic deformation giving rise to the observed EMR emissions.

An attempt to push back frontiers – digital near-ultraviolet aerial archaeology

Even though the sun has its peak emission of electromagnetic (EM) radiation in the visible waveband, it still produces a substantial amount of ultraviolet (UV) wavelengths (10–400 nm). However, the largest portion of this emitted energy is blocked by the ozone layer of the atmosphere, only allowing the near-ultraviolet or NUV (comprising the spectral band between 315 nm and 400 nm) to reach the earth's surface. Additionally, sensors acquiring this part of the UV wavelengths must be operated from low altitudes to minimize the effects of strong Rayleigh scattering to which the NUV radiation is subjected. Consequently, this waveband of the EM spectrum is rarely employed in aerial photography and its reflected portion only acquired in very specific applications. Archaeological aerial NUV imaging can thus truly be seen as a completely unexplored research field. Although it is far from certain that this technique could enhance, let alone reveal new archaeologically related anomalies, this paper discusses the practicalities of digital NUV imaging: from the modification of digital still cameras (DSCs) and the choice of appropriate optics over the extremely important NUV interference filters to the focus and exposure compensation needed. The use of a remotely controlled platform will be shown to be indispensable as the inevitable long shutter speed compels the use of such a very stable, unmanned aerial device. By presenting the very first aerial and archaeological digital NUV frames, the weaknesses and/or advantages over conventional visible imaging may be evident – notwithstanding the infancy of this approach.

Collective cavity mode excitations in arrays of Josephson junctions

We report on oscillations of a Josephson-junction system revealing a close analogy with fundamental effects known in laser physics. The experiments are performed on series arrays of junctions whose $IV$ curves show evidence of a mode in which all the junctions oscillate in synchronism on resonances appearing, in zero external magnetic field, at multiples of the first cavity mode. Evidence is provided that the mode is generated by collective oscillations which develop spontaneously because the frequencies of the modes are equal within a 1% uncertainty. Numerical simulations are employed to elucidate the reasons leading to the synchronous collective excitation and to explain why it is characterized by a low emission of electromagnetic radiation.

Binary Black Holes’ Effects on Electromagnetic Fields

In addition to producing gravitational waves, the dynamics of a binary black hole system could induce emission of electromagnetic radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as a possible enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.

The role of optical rectification in the generation of terahertz radiation from GaBiAs

We report on a detailed study of the emission of terahertz-frequency electromagnetic radiation from layers of GaBiyAs1−y (0≤y<0.04) grown by molecular beam epitaxy on (311)B and (001) GaAs substrates. We measure two orthogonally polarized components of the terahertz radiation emitted under excitation by ultrashort near-infrared laser pulses in both transmission and reflection geometries as a function of the crystal rotation about its surface normal as well as the effect of in-plane magnetic field and pump fluence on the terahertz emission. We conclude that the principal mechanism for terahertz generation is via optical rectification rather than transient currents.

Carbon nanotube as a Cherenkov-type light emitter and free electron laser

A mechanism of stimulated emission of electromagnetic radiation by an electron beam in carbon nanotubes is theoretically considered. Three basic properties of carbon nanotubes: a strong slowing down of surface electromagnetic waves, ballisticity of the electron motion over typical nanotube length, and extremely high electron current density reachable in nanotubes, allow proposition of them as candidates for the development of nanoscale Cherenkov-type emitters, analogous to traveling-wave tube and free electron laser. Dispersion equations of the electron-beam instability and the threshold conditions of the stimulated emission have been derived and analyzed, demonstrating realizability of the nanotube-based nano-free electron lasers at realistic parameters of nanotubes and electronic beams.

Materials Patterning and Characterisation at the Nanometre Scale Using Focused MeV Ion Beams: Present Achievements and Future Prospects

A key phenomenon in the interaction of MeV ions and solids is that the energy transferred from the primary ions to the target electrons is high compared with atomic and molecular binding energies, but low compared with the ion energy. This means that there is a high probability of modifying the chemical properties of the material (for patterning) or of inducing the emission of electromagnetic radiation (for analysis), yet the path of particle is changed by a negligible amount, which means that focused beams remain sharp even after penetrating long depths into the material. Developments in focusing MeV ions in recent years have pushed the useable beam diameters into the sub-micrometre region, which means that nuclear microbeams are poised to make an impact in both direct write fabrication and micro-analysis at length scales of interest in nanotechnology or microbiology. This paper reviews the science and technology underlying the use of nuclear microbeams (ion solid interactions, focusing systems) and reports on the present status and trends of applications in sub-micron scale applications.

Terahertz emission from silicon and magnesium doped indium nitride

We report an experimental study of femtosecond optically excited emission of terahertz frequency electromagnetic radiation from as-grown n-type InN, silicon doped InN, and magnesium doped InN. We have measured the terahertz emission from these materials as function of dc Hall mobility and carrier concentrations. Terahertz emission from InN:Si and native n-type InN increases with mobility as expected for transient photocurrents as primary mechanism of terahertz emission from InN. InN:Mg exhibits enhanced terahertz emission compared to InN:Si. This is experimental evidence for Mg being electrically active as an acceptor in InN. Terahertz emission from InN:Si is less strong than terahertz emission from native n-type InN because of an increased electron concentration due to silicon being an electrically active donor in InN.

Zitterbewegung of electrons in graphene in a magnetic field

Electric current and spatial displacement due to trembling motion [Zitterbewegung (ZB)] of electrons in graphene in the presence of an external magnetic field are described. Contributions of both inequivalent $K$ points in the Brillouin zone of graphene are considered. It is shown that, when the electrons are prepared in the form of wave packets, the presence of a quantizing magnetic field $B$ has very important effects on ZB. (1) For $B\ensuremath{\ne}0$ the ZB oscillations are permanent while for $B=0$ they are transient. (2) For $B\ensuremath{\ne}0$ many ZB frequencies appear while for $B=0$ only one frequency is at work. (3) For $B\ensuremath{\ne}0$ both interband and intraband (cyclotron) frequencies contribute to ZB while for $B=0$ there are no intraband frequencies. (4) Magnetic field intensity changes not only the ZB frequencies but the entire character of ZB spectrum. An emission of electromagnetic dipole radiation by the trembling electrons is proposed and described. It is argued that graphene in a magnetic field is a promising system for an experimental observation of Zitterbewegung.

Effects of strain rate and elevated temperature on electromagnetic radiation emission during plastic deformation and crack propagation in ASTM B 265 grade 2 titanium sheets

Some basic aspects of electromagnetic radiation (EMR) emission during quasi-static plastic deformation and crack propagation in ASTM B 265 grade 2 titanium sheets are reported in this paper. It has been observed that titanium emits several intermittent EMR signals starting near the yield and continuing up to fracture. The EMR emissions are sensitive to the applied strain rates. The number of EMR emissions shows a parabolic variation with strain rate, exhibiting a maxima. It appears that the temporary pinnings of the dislocations injected from the crack tip, which is essential for the emission of EMR as described in a recent model by the authors, do not adequately occur at high as well as low strain rates. At elevated temperatures, the square of the EMR amplitude is observed to be proportional to \( \exp {\left( { - {mU} \mathord{\left/ {\vphantom {{mU} {kT}}} \right. \kern-\nulldelimiterspace} {kT}} \right)}, \) where U is the activation energy for the movement of jogs, k the Boltzmann constant, T the temperature and m ≤ 1.0.