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Single layers of hexagonal two-dimensional nanostructures such as graphene, silicene, and germanene exhibit large carrier Fermi velocities and, consequently, large light-matter coupling strength making these materials promising elements for nano-optoelectronics. Although these materials are centrosymmetric, the spatial dispersion turns out to be quite large allowing the second-order noninear response of such materials to be comparable to the noncentrosymmetric 2D ones. The second-order response of massless Dirac fermions has been extensively studied, however, a general approach correct over the full Brillouin zone is lacking so far. To complete this gap, in the current paper, we develop a general quantum-mechanical theory of the in-plane second-order nonlinear response beyond the Dirac cone approximation and applicable to the full Brillouin zone of the hexagonal tight-binding nanostructures. We present explicit calculation of the nonlinear susceptibility tensor of 2D hexagonal nanostructures applicable to arbitrary three-wave mixing processes.

Slowing down the phase velocity of light in media has various applications. The generation of electromagnetic radiation using coherent Cherenkov mechanism is among them. Meanwhile, there is a need for compact terahertz radiation sources. Due to outstanding graphene properties, heterostructures consisting of alternating graphene/dielectric layers can operate as a medium for the generation of terahertz radiation. In the present paper, the slowing down and propagation coefficients for the modes supported in a two-layer graphene structure are studied. The study is conducted by means of the operator approach to wave propagation in stratified structures. The operator approach allows one to use coordinates-free notations and to consider consequently arbitrarily complex heterostructures (including anisotropic layers, for instance). The influence of interlayer distance and the value of graphene chemical potential on waves slowdown is determined. The obtained results open up prospects for creating a new type of terahertz radiation sources. Замедление фазовой скорости света в среде имеет различные применения. Среди них – генерация электромагнитного излучения с использованием когерентного черенковского механизма. В то же время существует потребность в компактных источниках терагерцового излучения. Благодаря уникальным свойствам графена гетероструктуры, состоящие из чередующихся слоев графен /диэлектрик, могут работать в качестве среды для этой цели. При помощи операторного метода получены коэффициенты замедления и распространения для мод, поддерживаемых в двухслойной графеновой структуре. Операторный подход позволяет использовать бескоординатные обозначения и, следовательно, работать со сколь угодно сложными гетероструктурами (включающими, например, анизотропные слои). Изучена зависимость степени замедления волн в графеновых сэндвич-структурах от межслойного расстояния и величины химического потенциала графена. Полученные результаты открывают перспективы для создания новых источников терагерцового излучения.

Heterostructures combining graphene layers, dielectric slabs and even metallic substrates are interesting systems to look at in view of their potential applications in microwaves and terahertz. A short review of their properties is presented, together with possible applications such as shielding layers, polarizers and plasmonic devices. In the near infrared and visible range, a graphene layer modifies the Brewster angle of the substrate that supports it. This effect leads to a non-destructive technique to count the number of atomic planes the graphene is made of.

International audience; This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record. ; The paper focuses on superlattices consisting of two coplanar fragments of one-layer graphene nanoribbons that have different width and are connected at an angle. Classification of such superlattices was carried out; their electronic properties were studied using the tight-binding method. It was demonstrated that in superlattices consisting of two fragments of graphene nanoribbons with armchair edges connected at an angle of 60°, the band gap can be regulated by the number of dimeric carbon atom chains of one of the fragments. In that case one can observe a periodic dependence of the band gap on the number of chains with a characteristic period equal to three dimeric chains. The number of dimeric chains of the second superlattice fragment regulates the average band gap value near which the periodic oscillations occur, as well as the amplitude of those oscillations. Therefore, one can accomplish a sufficiently precise band gap tuning for such structures. Such tuning can find its wide application in the booming carbon nanoelectronics industry when creating generators, amplifiers and sensors in the nanochains. ; This research was supported by projects FP7 ITN NOTEDEV(FP7-607521), CACOMEL(FP7-247007), FAEMCAR (FP7-318617) and CANTOR (FP7-612285); project H2020-MSCA-RISE-2014 CoExAN (SEP-210156718); European Graphene Flagship project (604391), as well as by the Belarusian Ministry of Education (grant 20140773), Belarusian State University (grant 11, 2014), and the international grant AFOSR “Nanosized CherenkovType Terahertz Light Emitter Based on Double-Walled Carbon Nanotubes and Bi-graphene Nanoribbons”.

It is shown that thin carbon coating with thicknesses, depending on its structure and porosity, ranging from tens of nanometres to tens of microns can absorb almost all incident microwave radiation without reflection. Special conditions on dielectric properties of substrate and conductivity of carbon material, which are necessary for the realisation of such a perfect absorber, are derived. The conductance of the carbon coating can then be controlled by proper porosity.

A great progress has been achieved during last two decade in the synthesis and fabrication of different nanostructured artificial materials with fascinating mechanical, electronic and optical properties irreducible to properties of bulk media. Accompanied by the impressive parallel development of the characterization techniques and measurement instrumentation, this process necessitates the revision of traditional concepts of physics and chemistry of condensed matter, adapting them to peculiarities of the nanoworld and significantly extending our knowledge of the nature of solids and our capabilities to control their properties.

We propose and demonstrate a new type of the a few micron thick carbon-based RF/microwaves/THz shields capable to absorb up to 50% of the incident radiation These are 30–35 nm thick films of pyrolytic carbon films, which are capable to secure about 60% attenuation in the Ka band mainly due to absorption of the microwave radiation. Another option is a sandwich-like structure comprised of multilayer graphene or ultrathin pyrolytic carbon films sandwiched between hundreds nanometers thick layers of dielectric. The microwave absorbance of such ultrathin and ultralight shields can further increased by depositing carbon-based shields onto a dielectric substrate with thickness comparable with the target wavelength. Specifically, the interference in the substrate allows us to achieve absorbance as high as 80% at 30GHz.

The localized plasmon resonance is studied in doped multi-walled carbon nanotubes in the high frequency terahertz range. The dependence of the resonance frequency on the tube length and chemical potential are demonstrated.

The ability of graphene and other nm-thin carbon films including pyrolytic carbon (PyC) and pyrolyzed photoresist (PPF) to absorb microwave radiation is discussed. We show that being deposited on a properly chosen optically transparent dielectric substrate these films can provide more than 20 dB electromagnetic interference (EMI) shielding efficiency (SE).

Terahertz lasing by electron beam propagating over a graphene/dielectric sandwich structure is considered. A dispersion equation for the surface electromagnetic modes propagating along graphene sheets is derived and Cerenkov synchronism between surface wave and electron beam is predicted at achievable parameters of the system. The generation frequency tuning is proposed by varying the graphene doping, the number of graphene sheets, the distance between sheets, etc.

Control of the band gap of graphene nanoribbons is an important problem for the fabrication of effective radiation detectors and transducers operating in different frequency ranges. The periodic edge-modified zigzag-shaped graphene nanoribbon (GNR) provides two additional parameters for controlling the band gap of these structures, i.e., two GNR arms. The dependence of the band gap E g on these parameters is investigated using the π-electron tight-binding method. For the considered nanoribbons, oscillations of the band gap E g as a function of the nanoribbon width are observed not only in the case of armchair-edge graphene nanoribbons (as for conventional graphene nanoribbons) but also for zigzag GNR edges. It is shown that the change in the band gap E g due to the variation in the length of one GNR arm is several times smaller than that due to the variation in the nanoribbon width, which provides the possibility for a smooth tuning of the band gap in the energy spectrum of the considered graphene nanoribbons. This is a post-peer-review, pre-copyedit version of an article published in [Physics of the solid state]. The final authenticated version is available online at: https://doi.org/10.1134/S106378341410028X

The interaction of Kα microwave radiation with ultrathin graphene films is studied. Although the thickness of these films is thousands of times smaller than the skin depth, they can absorb a significant fraction of the incident radiation. The possibility of controlling the amount of absorption and reflection of waves incident on graphene is demonstrated. In particular, by choosing the substrate parameters and the angle of incidence, it is possible to increase the absorption in graphene to >50%. For certain angles of incidence it is possible to have the TE-wave reflected, while the TM-wave is transmitted. These effects can be used to create ultrathin (atomic thicknesses) absorbers and polarizers.

The electromagnetic properties of graphene/PMMA multilayers are calculated by electrodynamics techniques. It is shown that an optimum number of layers exists for which the absorption of GHz radiations by the graphene planes is maximum.Numerical calculations using the rigorous coupledwave analysis method demonstrate that the absorption of GHz radiations by the optimum graphene/PMMA multilayer is robust in the sense that it does not depend on defects of the graphene planes to first order in concentration.

The pyrolytic carbon (PyC) films consisting of randomly oriented and intertwined graphene flakes with typical size of a few nanometers were synthesized by chemical vapor deposition (CVD) at 1100 °C on a quartz substrate. The discovered remarkably high absorption loss of up to 50 % of incident power along with chemical stability makes PyC films attractive for electromagnetic (EM) interference shielding in space and airspace communication systems as well as in portable electronic devices occupying this frequency slot.

A multi-walled carbon nanotube being effective slowing-down system is proposed as a potential candidate for nano-scale realization of Cherenkov-type emitter. The possibility of strong retardation of electromagnetic wave in multi-layer graphene is demonstrated. The quantum field approach is used for deriving the plasmon dispersion equation.

Microwave absorption properties of onion-like carbons (OLC) have been studied in microwave frequency range. A consistent analysis of the electromagnetic (EM) attenuation provided by OLC-based suspensions with variable concentration of OLC has been carried out in Ka-band (26-37 GHz). The first study of spectral features of the given suspensions (7.2-28.6 volume percents of OLC stuff in vaseline) demonstrates that the percolation threshold of OLC is strongly dependent on the average nanocarbon cluster size. It has been found also that raising the annealing temperature of a precursor nanodiamond leads to the enhanced absorption ability of onion-like carbon. The way to manipulate the OLC absorption ability through the OLC cluster size and nanodiamond annealing temperature is proposed for producing the effective EM coatings.

The dielectric properties of polymethyl methacrylate films with embedded onion-like carbon particles have been studied from 20 Hz to 1 MHz to investigate the structural relaxations of the composite material by varying the temperature between 240 and 520 K. The temperature behaviour of the complex permittivity at a given frequency is found to be strongly dependent on the nanocarbon concentration. A small effect of the onion-like carbon concentration on the beta transition of the polymer composite has been observed, which indicates that the included onion-like carbon particles do not block the rotational degrees of freedom of the ester groups along the polymer chains. By contrast, it has been found that embedding the nanocarbon fillers to the polymethyl methacrylate matrix changes significantly the alpha transition and the melting temperatures in a non-monoto-nous way.

Recently, superior electromagnetic attenuation of some types of onion-like carbon (OLC) in comparison to other carbon materials was reported, demonstrating a promising high potential of OLC for the design of electromagnetic shielding materials over a broad microwave (2−38 GHz) frequency range. This communication presents the first study of spectral features of OLC-polymethyl methacrylate (PMMA) composite films in the terahertz frequencies up to 3 THz, where the search of new operational materials and components is of particular importance for various promising applications.

Recently, a hypothetical nanoscale lasing device exploiting the emission of electromagnetic waves by electron beam in an isolated carbon nanotube (CNT) has been proposed [K.G. Batrakov, P.P. Kuzhir, S.A. Maksimenko, in: A. Lakhtakia, S.A. Maksimenko (Eds.), Proceedings of the SPIE, vol. 6328, 2006, p. 63280Z]. The present work considers the stimulated emission of an electron beam in CNT bundles. It is shown that the modification of electron wavefunction in CNT bundle as compared with isolated CNT can result in a significant change of the electron beam propagation in nanotubes. Two cases of the CNT collection arrangement—a “square” lattice and a densely packed bundle of CNTs—are discussed. The distribution of the electron density corresponding to four- and six-wave diffraction in the CNT collection is presented. The ranges where the electron scattering is suppressed are found to be preferable for lasing. The proposed way to increase the generation length extends substantially the potentiality of CNT bundle as a basic element of the nanoscale analog of the traveling wave tube (TWT), backward oscillator (BWO) and free-electron laser (FEL).

Stimulated emission of electron beam in isolated carbon nanotube (CNT) is considered. A concept of the CNT-based monomolecular light emitter—nanoscale traveling wave tube (TWT), backward oscillator (BWO) and free-electron laser (FEL) proposed for the first time in Batrakov et al. [in: A. Lakhtakia, S.A. Maksimenko (Eds.), Proceedings of the SPIE., vol. 6328, 2006, p. 63280Z]. is discussed in more details. Two possible basic mechanisms of the device operation—the undulator and the Cherenkov mechanisms of light emission—are considered. The particular emphasis is placed to the questions of matching of CNT and electron beam parameters in order to provide resonant conditions necessary for the radiative instability evolution. The influence of the beam energy spread on the dispersion characteristics and the starting current is revealed. Numerical calculations demonstrate that the electron beam spread larger than 3–5% influences significantly the generation process in the infrared frequency range at CNT lengths of the order of 10 μ m .

Electromagnetic response properties of carbon nanotubes (CNTs) are discussed. A basic approach to the problem is proposed synthesizing present‐day solid‐state physics and classical electrodynamics of nonhomogeneous mediums.[1] The developed theoretical model predicts the property of CNTs to be a strong slowing‐down system for surface waves[1,2] and allows proposing the physical schemes of the carbon nanotube use as monomolecular optoelectronic devices, such as a surface wave waveguide in IR frequency range, a monomolecular optical nanoantenna, a nanoantenna excitation device based on the Purcell effect, etc. A particular emphasis is given to the stimulated emission of electromagnetic waves by electron beam in nanotube. The significant retardation of the surface wave along with the ballistic character of the electron motion in nanotubes are shown[3] to be underlying the idea of the monomolecular light emitter with the Cherenkov lasing mechanism: the electrons in nanotube imposed to a realistic voltage can ...

Experimental observation of X-ray radiation from nonrelativistic (50–100 keV) electrons in crystals is reported and described as resulted from interference between parametric X-rays and coherent Bremsstrahlung . Possibility to tune X-rays frequency by crystal target rotation is demonstrated for the first time. Experiment details are discussed.

An experimental model of a tunable source of monochromatic x-rays was developed using nonrelativistic electrons passing through a single crystal silicon target. Theoretical predictions for x-ray output and characteristics were confirmed experimentally. The distinctive feature of the developed source is the possibility to tune x-ray frequency at fixed electron beam energy. In the present report, properties and potentialities of the developed source are considered. Copyright © 2007 John Wiley & Sons, Ltd.

Due to the importance of satellite communication, electromagnetic compatibility in the Ka band (26 to 37 GHz) has recently become an important concern. We analyze the EM shielding effectiveness in the Ka band of highly amorphous nanometrically thin pyrolytic carbon (PyC) films, which consists of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers. We displayed that the manufactured PyC films, whose thickness is thousand times less than the skin depth of conventional metals, provide a reasonably high EM attenuation. We demonstrate theoretically and observed experimentally that up to 50% of microwave power can be absorbed in a conductive film with thickness much smaller than the skin depth. Different possibilities of the effect enhacement are discussed.

Current trends in Nan electro magnetics - a new field of research synthesizing classical radio physics and electrodynamics with quantum theory of solids, physical kinetics, quantum chemistry, computational mathematics - are analyzed with the focus on applications in the terahertz frequency range. The analysis is exemplified by the discussion of the THz response peculiarities of carbon nanostructures and composite materials with nanocarbon fillers. Some electromagnetic applications of nancaerbons are discussed, such as nanoantennas, amplifiers and generators of terahertz radiation, THz range functional materials for radar absorbing and reflective coatings.

Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to variety of reasons. Using the orthogonal tight-binding method for $\pi$-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of such ribbons was proposed and band gaps for applied fields up to the SiO$_2$ breakdown strength ($1$ V/nm) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some type of jagged graphene nanoribbons in the external electric field that lays in the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to $0.6$ eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap., Comment: 15 pages, 12 pdf figures

Feasibility of the conception of the volume free electron laser was verified by “OLSE-10” experimental prototype. Measurements of key parameters of the microwave radiation of the prototype have confirmed the features predicted theoretically. Possibility of smooth tuning of the radiation frequency and decrease of the threshold current density in a volume free electron laser are demonstrated. The set of VFEL characteristics showed that it might be the prospective source of tuneable polarized radiation in the microwave and Terahertz ranges [V.G. Baryshevsky, K.G. Batrakov, A.A. Gurinovich, et al., Nucl. Instr. and Meth. A 507 (2003) 137; V.G. Baryshevsky, A.A. Gurinovich, LANL e-print archive: physics/0409107 ; V.G. Baryshevsky et al., LANL e-print archive: physics/0409125 ]. Application of radiation of these wavelength ranges in science and engineering is highly challenging.

The generation of induced radiation in volume resonator formed by metal threads is considered. It is shown that using of such volume diffraction grating allows increasing of lasing efficiency in terahertz range. The requirements on beam and grating parameters are obtained., Latex, 2 eps figures, to be presented at FEL2002 Conference

© 2017 Society of Photo-Optical Instrumentation Engineers (SPIE). The influence of chemical vapor deposition (CVD) graphene grain size on the electromagnetic (EM) shielding performance of graphene/polymethyl methacrylate (PMMA) multilayers in K a -band was studied both experimentally and theoretically. We found that increasing the average graphene grain size from 20 to 400 μm does not change the EM properties of heterostructures consisting of graphene layers sandwiched between submicron thick PMMA spacers. The independence of EM interference shielding effectiveness on the graphene grain size between 20 and 400 μm allows one to use cheaper (or more convenient regimes of CVD) graphene samples with low crystallinity and small grain size in the development of new graphenebased passive EM devices operated at high frequencies.

The ability of thin conductive films, including graphene, pyrolytic carbon (PyC), graphitic PyC (GrPyC), graphene with graphitic islands (GrI), glassy carbon (GC), and sandwich structures made of all these materials separated by polymer slabs to absorb electromagnetic radiation in microwave-THz frequency range, is discussed. The main physical principles making a basis for high absorption ability of these heterostructures are explained both in the language of electromagnetic theory and using representation of equivalent electrical circuits. The idea of using carbonaceous thin films as the main working elements of passive radiofrequency (RF) devices, such as shields, filters, polarizers, collimators, is proposed theoretically and proved experimentally. The important advantage of PyC, GrI, GrPyC, and GC is that, in contrast to graphene, they either can be easily deposited onto a dielectric substrate or are strong enough to allow their transfer from the catalytic substrate without a shuttle polymer layer. This opens a new avenue toward the development of a scalable protocol for cost-efficient production of ultralight electromagnetic shields that can be transferred to commercial applications. A robust design via finite-element method and design of experiment for RF devices based on carbon/graphene films and sandwiches is also discussed in the context of virtual prototyping.

Thanks to its high electrical conductivity, a graphene plane presents a good shielding efficiency against GHz electromagnetic radiations. Several graphene planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties of isolated graphene. Maximum absorption of radiations for frequency around 30 GHz is achieved with six separated graphene planes, which is the optimum number. This remarkable result is demonstrated experimentally from electromagnetic measurements performed in the Ka band on a series of multilayers obtained by piling 1, 2, 3 ⋯ graphene/PMMA units on a silica substrate. Theoretical calculations convincingly explain the observed absorption and transmission data in the GHz domain. It is concluded that graphene/PMMA multilayers can be used as an efficient optically transparent and flexible shielding media.

Different mechanisms of terahertz emission from carbon nanotubes (CNTs) in the presence of electric and magnetic fields are discussed. A nanoscale lasing device of Cherenkov type exploiting the emission of electromagnetic waves in the terahertz range by electron beam in an isolated multi-wall CNT and CNT bundles is proposed.

Ultrafast quantum dynamics of interband transitions in monolayer graphene initiated by strong laser radiation is investigated. A microscopic theory describing nonlinear interaction beyond the Dirac cone approximation and applicable to the full Brillouin zone of the hexagonal nanostructure with tight-binding electronic states is developed. Coherent effects toward the control of macroscopic quantum states in graphene are considered. In particular, we consider Rabi oscillations, rapid adiabatic passage for population transfer, and multiphoton excitation of the Fermi-Dirac sea in a monolayer graphene.

VFEL lasing in system with dynamical undulator is described. In this system radiation of long wavelength creates the undulator for lasing on shorter wavelength. Two diffraction gratings with different spatial periods form VFEL resonator. The grating with longer period pumps the resonator with long wavelength radiation to provide necessary amplitude of undulator field. The grating with shorter period makes mode selection for short wavelength radiation. Lasing of such a system in terahertz frequency range is discussed., 2 eps figures, to be presented at FEL2002

We consider the effects of the deuteron (Ω− hyperon) spin rotation and oscillations at the matter which is proportional to the real part of the spin-dependent forward scattering amplitude. That gives a possibility of a direct measurement of this quantity. Spin-dependent forward scattering amplitude of the polarized deuteron (Ω− hyperon) on an unpolarized proton is determined by the nucleon-nucleon (quark-quark) rescattering, nonsphericity of the deuteron (Ω− hyperon) and spin-dependent nucleon-nucleon (quark-quark) scattering amplitude. Thus spin oscillation phenomenon represents a method for N-N (quark-quark) scattering amplitude investigation, including its real part, over a broad energy range.

Characteristics of the X-ray tunable source on the basis of parametric radiation from non-relativistic electrons in a crystal are considered. Theoretical interpretation of experimental X-ray spectra in the transmitted electron microscope with the crystal foil as a target is considered. Conditions for the kinematical decrease of the radiation line width due to electron multiple scattering are also described.

The microscopic theory of bilayer graphene nonlinear interaction with coherent electromagnetic radiation is developed. The Liouville--von Neumann equation for a single-particle density matrix in the multiphoton resonant approximation is solved. We consider low-energy excitations of a Fermi-Dirac sea with THz pump radiation. The obtained solutions disclose Rabi oscillations and resonant multiphoton excitations of a Fermi-Dirac sea in bilayer graphene. On the basis of numerical simulations we examine the rates of high-harmonic radiation at particle-hole annihilation in the field of a strong pump wave. We show that in the THz domain of frequencies one can achieve efficient generation of high harmonics with pump waves of moderate intensities.

Surface plasmons can be used for generation of radiation by \( \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{\text{C}} \)erenkov mechanism in carbon nanotubes. However, slowing down of the plasmon phase speed is not enough for the synchronization with a nonrelativistic electron beam. Using the density-matrix formalism and the tight-binding approximation, we developed the method of obtaining the dispersion equation for plasmons in n-layer graphene systems. It was found that a graphene single layer can reduce the surface plasmon phase speed by 3–6 times. Reduction up to the Fermi velocity of p-electrons is achieved in spatially separated graphene bilayer. Thus, graphene bilayer seems to be suitable material for realization of the \( \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{\text{C}} \)erenkov-type emitters in nanoscale.

A parametric quasi-Cherenkov free electron laser with surface diffraction distributed feedback is studied when an electron beam moves over the target surface. The parameters of such a device using the Los Alamos Advanced Free Electron Laser (AFEL) linac are given.

The boundary problem for an X-ray crystal quasi-Cherenkov FEL is solved for the case in which distributed feedback is provided by three-wave coplanar diffraction of the emitted photons. In comparison with two-wave distributed feedback, it is shown in the three-wave case that the necessary interaction region between a particle beam and the electromagnetic wave necessary to reach the oscillation threshold, as well as radiation losses inside the medium, can be reduced with an appropriate choice of parameters. This gives rise to the possibility of relaxing the required parameters of a particle beam necessary for lasing in the X-ray spectral range. At the same time it also allows a reduction in the size of an FEL and the construction of more compact coherent radiation sources in any spectral range.

A new type of light-weight material produced by 3D printing consisting of nano-carbon doped polymer layer followed by a dielectric polymer layer is proposed. We performed temperature dependent characterization and measured the electromagnetic (EM) response of the samples in the GHz and THz range. The temperature dependent structural characteristics, crystallization, and melting were observed to be strongly affected by the presence and the number of nano-carbon doped layers in the sandwich structure. The electromagnetic measurements show a great potential of such a type of periodic material for electromagnetic compatibility applications in microwave frequency range. Sandwich structures containing only two nano-carbon layers already become not transparent to the microwaves, giving an electromagnetic interference shielding efficiency at the level of 8–15 dB. A sandwich consisting of one nano-carbon doped and one polymer layer is opaque for THz radiation, because of 80% of absorption. These studies serve as a...

Fresnel equations predict that an ultrathin free standing conductive film, thousands times thinner than skin depth, is capable to absorb up to 50% of incident electromagnetic radiations. In the microwave range, the same holds true for a free standing graphene sheet. We demonstrate theoretically and prove experimentally that microwave absorptance of graphene can be enhanced considerably by depositing graphene on a dielectric substrate. On the experimental side, we obtain 80% and 65% absorptance at 30GHz and 1 THz, respectively. Theory predicts that higher absorptance can be achieved with a suitable choice of the dielectric permittivity and the thickness of the substrate. Absorption can also be maximized by choosing the optimum incidence angle for s-polarized waves in free space or by working in the vicinity of the cut-off frequency of the transverse electric mode in waveguide configuration. The polarization sensitivity of the transmittance and reflectance of graphene layers can be used to tune the polarization state of the transmitted and reflected radiations.

The idea and principles of volume free electron lasers were proposed in [1-4]. It was shown there that volume distributed feedback (VDFB) can essentially reduce the threshold current of generation and provide the possibility of smooth frequency tuning. The present work considers an undulator VFEL with multiwave VDFB. It is shown that dependence of threshold current on the interaction length changes in the point of roots degeneration. This leads to the sharp decrease of start current if condition of dynamical diffraction is fulfilled. The dependence of amplification coefficient changes, too. So the interaction length for generation appears shorter. The proposed scheme can be used for generation in wide spectral range from microwaves to X-rays. The operating features of undulator VFEL is considered., Latex, 6 pages with 2 Postscript figures

First lasing of a volume free electron laser in the millimeter wavelength range is observed.