Search

This paper is aimed at investigating the role of electrons in creation of currents in plasma equilibria with high plasma pressure (β ≈ 1). Despite the long history of studies of these equilibria, there is still no consensus on what kind of particle species is responsible for the creation of the diamagnetic current and what characteristic size the current layer should have. For example, simulations of isothermal plasma injection into a multi-cusp magnetic trap [J. Park et al., Front. Astron. Space Sci. 6, 74 (2019)] demonstrate the formation of a transition layer with a thickness comparable to the electron Larmor radius, where the equilibrium current is carried by electrons. At the same time, studies of a diamagnetic bubble created by a hot-ion plasma in a mirror trap [I. Kotelnikov, Plasma Phys. Control Fusion 62, 075002 (2020)] assume ion dominance and completely ignore electron currents. In this paper, we show that the equilibrium initially governed by the ion diamagnetic current is unstable against perturbations at the ion-cyclotron frequency harmonics, and this instability forces the plasma to come to a new equilibrium state in which the current is mainly created by the E × B -drift of electrons. The same type of equilibrium is also found to form in a more realistic problem setup when plasma is continuously injected into the uniform vacuum magnetic field. [ABSTRACT FROM AUTHOR]

This paper discusses optimal conditions for setting up a laboratory experiment on the generation of narrow-band THz radiation due to the head-on collision of two plasma wakes excited by a pair of femtosecond laser pulses in a supersonic helium jet. In this case, emission of electromagnetic waves at the second harmonic of the plasma frequency is caused by nonlinear interaction of counterpropagating plasma waves having different transverse potential profiles in the focus of the laser beams. Using particle-in-cell simulations, we study how strongly the efficiency of laser-to-terahertz energy conversion in this scheme is affected by the inhomogeneous electron density profile arising during field ionization of helium, as well as by the time-delay between arrivals of laser pulses to the focal point. [ABSTRACT FROM AUTHOR]

In this paper, the spectral properties of the triangular lattice of grana are investigated. By the finite difference time domain method, the transmittance spectra of the structure are calculated and the components of the scattering matrix are determined, which makes it possible to determine the effective parameters of the structure. As a result, it was shown that a two-dimensional lattice of grana can be represented as a homogeneous film with a thickness equal to the height of the grana. It is shown that the positions of the resonances before and after the homogenization of the structure coincide, which makes this method attractive for estimated calculations of the structure. [ABSTRACT FROM AUTHOR]

Electromagnetic emission at the second harmonic of the plasma frequency produced by nonlinear interaction of counterpropagating laser-driven potential plasma waves are studied using particle-in-cell simulations. This process has been recently proposed as a method for generating high-power tunable THz radiation with a narrow spectral line-width (Timofeev et al 2017 Phys. Plasmas 24 103106). In the present paper, we find the optimal conditions for demonstrating this phenomenon in a laboratory experiment that implies excitation of colliding wakefields by axially symmetric 830 nm Gaussian laser pulses with the total energy 0.2 J in a supersonic gas jet. It is shown that the emission mechanism based on the collision of different-size wakes is always accompanied with the mechanism of plasma antenna which begins to radiate electromagnetic waves after the build-up of periodic ion density modulation. Such additional emission makes hydrogen more attractive for this generating scheme than gases with heavier atoms. [ABSTRACT FROM AUTHOR]

In this study, we investigate the generation of electromagnetic emission near the second harmonic of the plasma frequency induced by pairs of counter-propagating electron beams. Such systems can naturally occur in cosmic plasmas when particle acceleration regions are closely spaced, and they can also be implemented in a laboratory device. We specifically focus on the regime where the oblique beam–plasma instability dominates. The emission mechanism relies on the coalescence of counter-propagating plasma waves with different transverse structures. It has been demonstrated that the parameters of the system necessary for efficient radiation generation can be determined using the exact linear theory of beam–plasma instability. Through particle-in-cell numerical simulations, we show that a high beam-to-radiation conversion efficiency can be achieved when the beams excite small-scale oblique plasma oscillations. Importantly, we find that the efficiency and spectral characteristics of the radiation are not dependent on the thickness of the beams. We explore two scenarios involving pairs of symmetric beams: one with relativistic beams having a directed velocity of v b = 0.9 c and another with sub-relativistic beams at v b = 0.7 c. Additionally, we consider the injection of two beams with different velocities. In all cases considered, the beam-to-radiation power conversion efficiency reaches a level of a few percent, a sufficiently high value for beam–plasma systems. [ABSTRACT FROM AUTHOR]

In this paper, electromagnetic emissions produced by a beam-plasma system are investigated using particle-in-cell simulations for the particular case when the typical transverse size of both the 100 keV electron beam and the produced plasma channel is comparable to the radiation wavelength. The interest in this regime of beam-plasma interaction is associated with highly efficient generation of electromagnetic waves near the plasma frequency harmonics that has been recently observed in laboratory experiments on the GOL-3 mirror trap. It has been found that the radiation power only from the vicinity of the doubled plasma frequency in these experiments can reach 1% of the total beam power. Subsequent theoretical and simulation studies have shown that the most likely candidate for explaining such efficient generation of electromagnetic radiation is the mechanism of a beam-driven plasma antenna based on the conversion of the most unstable plasma oscillations on a longitudinal density modulation of plasma ions. In this paper, we investigate how effectively this mechanism can work in a real experiment at the GOL-3 facility, when a thin subrelativistic electron beam gets a large angular spread due to compression by a magnetic field, and the gas into which it is injected has macroscopic density gradients. [ABSTRACT FROM AUTHOR]

In an initially uniform plasma, the lifetime of a weakly nonlinear plasma wave excited by a short driver is limited by the ion dynamics. The wakefield contains a slowly varying radial component, which results in a perturbation of the ion density profile and consequent destruction of the plasma wave. We suggest a novel method of characterizing the wave lifetime in numerical simulations quantitatively and study how the lifetime scales with the ion mass. We also discuss the implications of the limited lifetime on a recently proposed method of generating high-power terahertz radiation with counterpropagating wakefields driven by colliding laser pulses. [ABSTRACT FROM AUTHOR]

It is found that nonlinear interaction of plasma wakefields driven by counterpropagating laser or particle beams can efficiently generate high-power electromagnetic radiation at the second harmonic of the plasma frequency. Using a simple analytical theory and particle-in-cell simulations, we show that this phenomenon can be attractive for producing high-field (~10 MV/cm) tunable terahertz radiation with a narrow line width. For laser drivers produced by existing petawatt-class systems, this nonlinear process opens the way to the generation of gigawatt, multi-millijoule terahertz pulses which are not presently available for any other generating schemes. [ABSTRACT FROM AUTHOR]

In this paper, electromagnetic emissions produced in a thin beam-plasma system are studied using two-dimensional particle-in-cell simulations. For the first time, the problem of emission generation in such a system is considered in a realistic formulation allowing for the continuous injection of a relativistic electron beam through a plasma boundary. Specific attention is given to the thin plasma case in which the transverse plasma size is comparable to the typical wavelength of beam-driven oscillations. Such a case is often implemented in laboratory beam-plasma experiments and has a number of peculiarities. Emission from a thin plasma does not require intermediate generation of the electromagnetic plasma eigenmodes, as in an infinite case, and is more similar to the regular antenna radiation. In this work, we determine how efficiently the fundamental and the second harmonic emissions can be generated in previously modulated and initially homogeneous plasmas. [ABSTRACT FROM AUTHOR]

The ways to improve the efficiency of electromagnetic waves generation in laboratory experiments with high-current relativistic electron beams injected into a magnetized plasma are discussed. It is known that such a beam can lose, in a plasma, a significant part of its energy by exciting a high level of turbulence and heating plasma electrons. Beam-excited plasma oscillations may simultaneously participate in nonlinear processes resulting in a fundamental and second harmonic emissions. It is obvious, however, that in the developed plasma turbulence the role of these emissions in the total energy balance is always negligible. In this paper, we investigate whether electromagnetic radiation generated in the beam-plasma system can be sufficiently enhanced by the direct linear conversion of resonant beam-driven modes into electromagnetic ones on preformed regular inhomogeneities of plasma density. Due to the high power of relativistic electron beams, the mechanism discussed may become the basis for the generator of powerful sub-terahertz radiation. [ABSTRACT FROM AUTHOR]

A large number of model particles are shown necessary for quantitatively correct simulations of the kinetic beam-plasma instability with the clouds-in-cells method. The required number of particles scales inversely with the expected growth rate, as only a narrow interval of beam velocities is resonant with the wave in the kinetic regime. [ABSTRACT FROM AUTHOR]

Efficiency of electromagnetic emission produced in a magnetized plasma with counterstreaming electron beams was investigated using both the linear kinetic theory and particle-in-cell simulations. We calculated the growth rate of the beam-plasma instability taking into account both kinetic and relativistic effects and showed that there exists a regime in which transversely propagating electromagnetic waves can be generated by the coupling of the most unstable oblique beam-driven modes. It was confirmed by numerical simulations that such a tune-up of system parameters for a specific nonlinear process can lead to a substantial increase in electromagnetic emission efficiency. It was found that electromagnetic radiation emerging from the plasma in such a regime is generated near the harmonics of the pump frequency that is determined by the typical eigenfrequency of the beam-driven modes. It was also shown that the peak emission power can reach 5% of the maximal power lost by beam electrons. [ABSTRACT FROM AUTHOR]

Optical properties of 2D nanocomposite-based photonic crystals with a lattice defect are studied. The nanocomposite comprises metallic nanospheres dispersed in a transparent matrix and is characterized by an effective resonant permittivity. Transmission spectrum for s-polarized waves at oblique incidence is calculated. Spectral manifestation of the splitting of the defect mode when its frequency coincides with the resonant frequency of the nanocomposite is studied. The essential dependence of the splitting on the angle of incidence and concentration of metallic nanospheres in the nanocomposite matrix is established. Specific features of spatial distribution of the electric field intensity in defect modes of crystals are analyzed. [ABSTRACT FROM AUTHOR]

Efficiency of collective beam-plasma interaction strongly depends on the growth rates of dominant instabilities excited in the system. Nevertheless, exact calculations of the full unstable spectrum in the framework of relativistic kinetic theory for arbitrary magnetic fields and particle distributions were unknown until now. In this paper, we give an example of such a calculation answering the question whether the finite thermal spreads of plasma electrons are able to suppress the fastest growing modes in the beam-plasma system. It is shown that nonrelativistic temperatures of Maxwellian plasmas can stabilize only the oblique instabilities of relativistic beam. On the contrary, non-Maxwellian tails typically found in laboratory beam-plasma experiments are able to substantially reduce the growth rate of the dominant longitudinal modes affecting the efficiency of turbulent plasma heating. [ABSTRACT FROM AUTHOR]

Basic mechanisms of turbulent plasma heating by powerful electron beams are studied using numerical simulations. Both particle-in-cell and hybrid codes are used to investigate how beam-plasma instability evolves and saturates in the case of continuously injected electron beam. For sufficiently high plasma temperature beam driven turbulence is found to operate in the regime of the constant pump, when the saturation level of heating power is determined solely by the nonlinear interaction of beam particles with resonant waves and does not depend on the turbulence structure in the nonresonant part of the spectrum. [ABSTRACT FROM AUTHOR]

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed. [ABSTRACT FROM AUTHOR]

The band structure of two-dimensional resonant photonic crystals of two types has been calculated using the expansion of eigenfunctions in plane waves. Crystals of one type consist of infinite dielectric cylinders forming a square lattice filled with a resonant gas, and crystals of the other type consist of infinite cylindrical holes filled with a resonant gas and forming a square lattice in a dielectric matrix. It has been shown that, in both cases, the dispersion of a resonant gas in combination with the dispersion of a two-dimensional structure with a photonic band gap leads to the appearance of an additional narrow transmission band near the edge of the band gap or an additional band gap in the continuous spectrum of the photonic crystal. The calculations performed have demonstrated that new dispersion properties substantially depend on the density of the resonant gas, the position of the resonant frequency with respect to the edge of the band gap, and the direction of propagation of electromagnetic waves. [ABSTRACT FROM AUTHOR]

The fully kinetic, fully electromagnetic dispersion equation for a warm relativistic electron beam in a cold magnetized plasma is numerically solved with no simplifying assumptions made. For magnetic fields of various strengths, the growth rate maps for the beam-plasma instability are plotted and dominant modes are identified. The exact solution is compared with available approximate solutions. The latter are shown to misinterpret the effect of the magnetic field on the instability of oblique waves. [ABSTRACT FROM AUTHOR]

The eigenexcitation and transmission spectra of a one-dimensional resonant photonic crystal are studied for TM and TE polarized electromagnetic waves. The crystal considered is a layered structure consisting of alternating isotropic layers and layers of a resonantly absorbing gas. The performed calculations show that the band structure of the spectra of the resonant photonic crystal significantly changes as the angle of incidence and the density of the resonant gas are varied. The structure of the spectra of additional transmission in the bandgap of the resonant photonic crystal is studied taking into account the decay of electromagnetic modes. The possibilities of controlling the spectrum of electromagnetic modes are indicated. [ABSTRACT FROM AUTHOR]

A model for collective relaxation of high-power relativistic electron beams in plasmas is proposed, which describes beam-plasma interaction in the regime when amplitudes of unstable waves are large enough to trap beam electrons. The distinctive feature of this regime is that the power lost by beam electrons as they interact with exited wave packets weakly depends on the energy of these packets. This makes the model insensitive to the nature of nonlinear processes in plasma, which are responsible for saturation of the beam instability. The model is thus rather universal and suitable for quantitative comparison with the experimental data. The predicted profiles of energy release along the plasma column are in a good quantitative agreement with the ones measured at various experimental facilities. [ABSTRACT FROM AUTHOR]

The effect of fractional stimulated Raman adiabatic passage in an optically dense medium of three-level Λ atoms is shown to result in the maximum coherence on the Raman transition on a length of the medium that considerably exceeds the length of linear resonant absorption. The general case of unequal oscillator strengths of the adjacent transitions is analyzed. The results are of interest for coherent anti-Stokes Raman spectroscopy with delayed pulses. [ABSTRACT FROM AUTHOR]

The article reports on electromagnetically induced transparency and controlling the time shape of laser pulses. The development of new methods for controlling optical properties of a medium and the time shape of laser pulses is an important physical problem of fundamental and applied significance. The solution of this problem is urgently required in the areas of spectroscopy of fast processes, quantum control of atoms and molecules, optoelectronics and optical communication, etc. In this article, researchers discussed a new possibility for controlling the shape and duration of laser pulses on the basis of the electromagnetically induced transparency phenomenon.

The spatiotemporal propagation dynamics of a weak probe pulse in an optically dense medium of three-level atoms is studied in the adiabatic approximation under conditions of electromagnetically induced transparency. The atomic coherence induced at the dipole-forbidden transitions is found to be spatially localized. This effect is used for the analysis of the reversible writing (reading) of short optical pulses. The method of pulse time reversal is suggested. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Features of the adiabatic population transfer are studied with the spatial evolution of interacting pulses propagating in an optically dense medium of three-level A-atoms taken into account. A self-consistent analytical solution describing the spatial-temporal dynamics of interacting short pulses under the conditions of adiabatic population transfer is constructed in the adiabatic approximation with consideration for the first nonadiabatic correction. Practically complete inversion on a forbidden transition determined by coherent (adiabatic) population transfer is shown to take place over a length of the medium, which may exceed the absorption length of a weak probing pulse in the absence of control radiation on the adjacent transition by several orders of magnitude. [ABSTRACT FROM AUTHOR]

The content and spatial distribution of 15 heavy metals and metalloids (HMMs) in the upper soil layer (0–10-cm) were determined by data of the geochemical survey in the city of Severobaikal'sk (Republic of Buryatia) in the summer of 2018. The priority pollutants of the topsoil in Severobaikal'sk are Sb, Pb, and W. Soils of the transport, industrial, and single-story residential zones are most strongly polluted. The intensive accumulation is typical for Sb, Pb, and Cu in the first two zones and for Sb, W, Pb, Cd, and Zn in the single-story residential zone. Three associations of HMMs—V–Cr–Co–Ni–Mn; Zn–Cd–Pb; and Sn–Sb–Mo—are inputted from the same sources, and their distribution in the soil cover of the city is similar. The accumulation of HMMs in the upper layer of urban soils is controlled by the content of Fe oxides, Corg, pH, and the type of land use, which determines the sources and level of anthropogenic impact on soils. The technogenic impact causes a change in the properties of urban soils, which enhances their ability to fix HMMs. There is no environmental hazard of soil pollution with HMMs for the city, but soils with low and moderately hazardous pollution levels occupy a third of the area of the single-story residential and industrial zones. Formation of several contrasting multielemental anomalies in soils on the bank of the Tyya River and near Lake Baikal is a danger for their waters due to the possibility of the inflow of toxic metals with surface and subsurface runoff. [ABSTRACT FROM AUTHOR]

This paper reports on the generation of a directed flux of electromagnetic radiation with an energy content of 10 J in the frequency range of 0.2–0.3 THz at a microsecond pulse duration in a beam–plasma system. The flux is generated when a relativistic electron beam (REB) pumps electron plasma waves in a magnetized plasma column. In the described experiments, this fundamentally new approach to generate terahertz radiation was carried out at the GOL-PET facility in the conditions of varying the beam current density and the plasma density in the appropriate ranges of 1–2 kA/cm2 and 1014–1015 cm–3. From the comparison of the flux energy spectrum measured experimentally in the frequency range 0.15–0.45 THz with the calculated one obtained using the previously proposed model of radiation generation in a beam–plasma system it was shown that this process occurs through resonant pumping by REB of precisely the branch of upper-hybrid plasma waves. Mastering this new method to generate terahertz radiation opens the prospect of its use to obtain multi-megawatt radiation fluxes in the frequency range up to 1 terahertz and higher. For such a development approach the most promising beam for pumping plasma oscillations seems to be a kiloampere REB generated in a linear induction accelerator. [ABSTRACT FROM AUTHOR]

wolfram cellular automata are considered and their operation is demonstrated using an example of traffic flow simulation. For the class of one-dimensional elementary cellular automata, the concept of linearity is introduced in the language of Zhegalkin operators. An algorithm for finding linear Zhegalkin operators with multipliers of three variables is presented. The algorithm is implemented in Python. [ABSTRACT FROM AUTHOR]

The polarized optical states in the transmission spectrum of a twisted-nematic Fabry-Pérot cavity with the distinctly broken Mauguin’s waveguide regime have been theoretically and experimentally investigated. Specific features of the electric field-induced transformation of the polarization and spectral characteristics of eigenmodes of the neighboring series at the overlap resonant frequencies have been examined. It is demonstrated that the linear polarizations of eigenmodes at the cavity boundaries remain nearly orthogonal and their frequency trajectories reproduce the avoided crossing phenomenon. The experimental data are confirmed analytically and by the numerical simulation of light transmission through the investigated anisotropic multilayer with the use of a Berreman matrix method. The results obtained can be generalized to any materials with the helix response. [ABSTRACT FROM AUTHOR]

Three-wave interactions between Langmuir and electromagnetic waves in plasma with unstable electron flows are believed to be the main cause of type II and III solar radio emissions. The narrow band of type II bursts requires assuming that this radiation is generated in some local regions of shock fronts traveling in the solar corona, where the specific conditions for the enhancement of electromagnetic emissions near the plasma frequency harmonics are created. The reason for such enhancement at the second harmonic may be the formation of counterstreaming electron beams. There are different opinions in the literature on whether the second harmonic electromagnetic emission in the presence of an additional beam can be efficient enough to markedly dominate emissions produced by a single beam. In the present paper, we carry out particle-in-cell simulations of the collision of two symmetric electron beams in plasma with open boundary conditions and show that the efficiency of beam-to-radiation power conversion can be significantly increased compared to models with periodic boundary conditions and reach the level of a few percent if three-wave interactions with electromagnetic waves near the second harmonic of the plasma frequency becomes available for the most unstable, oblique, beam-driven modes. [ABSTRACT FROM AUTHOR]

We consider a layered metal–dielectric microcavity with a liquid crystal used as a resonator layer. The transformation of the microcavity spectra is shown experimentally using three methods, namely, mechanical rotation of the sample, heating, and applying external voltage. The obtained spectra exhibit multiple vanishing resonant lines. It is found the vanishing resonant lines are not a spectral manifestation of the bound state in the continuum for this system. Despite the absence of true bound states in the continuum, an experimental tuning of the resonance Q factor via changing the radiation loss rate is demonstrated through variation of the optical properties of the liquid crystal layer. [ABSTRACT FROM AUTHOR]

It is found that multi-cycle pulses of high-power coherent terahertz radiation can be efficiently generated in a plasma by counterstreaming long-pulse electron beams driving potential plasma waves via the two-stream instability. Instead of the well-known three-wave interaction processes between oblique beam-driven modes, we propose to generate electromagnetic radiation near the doubled plasma frequency due to the novel and much more efficient mechanism based on the head-on collision of longitudinal plasma waves with mismatching potential profiles. It is shown that this radiation mechanism can be implemented experimentally either by the collision of low-density electron beams with different transverse sizes or by the counter injection of denser equal-size beams unstable against filamentation perturbations. Particle-in-cell simulations for kiloampere electron beams capable of focusing into millimeter-scale sizes demonstrate the possibility to reach the high efficiency of beams-to-THz power conversion (3%–7%), which opens the path to gigawatt-class THz sources with a narrow spectral line. [ABSTRACT FROM AUTHOR]

A model of an organic solar cell based on a Tamm plasmon polariton localized at the boundary of the active layer doped with plasmonic nanoparticles and a multilayer mirror is proposed. It is shown that the integral absorption in the active layer can be increased by 10% compared to the optimized planar solar cell. [ABSTRACT FROM AUTHOR]

The impact of superthermal electrons on dispersion properties of isotropic plasmas and on the modulational instability of a monochromatic Langmuir wave is studied for the case when the power-law tail of the electron distribution function extends to relativistic velocities and contains most of the plasma kinetic energy. Such an energetic tail of electrons is shown to increase the thermal correction to the Langmuir wave frequency, which is equivalent to the increase of the effective electron temperature in the fluid approach, and has almost no impact on the dispersion of ion-acoustic waves, in which the role of temperature is played by the thermal spread of low-energy core electrons. It is also found that the spectrum of modulational instability in the non-maxwellian plasma narrows significantly, as compared to the equilibrium case, without change of the maximum growth rate and the corresponding wavenumber. [ABSTRACT FROM AUTHOR]

Nonlinear interaction of a low density electron beam with an uniform plasma is studied using two-dimensional particle-in-cell simulations. We focus on formation of coherent phase space structures in the case, when a wide two-dimensional wave spectrum is driven unstable, and we also study how nonlinear evolution of these structures is affected by the external magnetic field. In the case of isotropic plasma, nonlinear buildup of filamentation modes due to the combined effects of two-stream and oblique instabilities is found to exist and growth mechanisms of secondary instabilities destroying the Bernstein-Green-Kruskal-type nonlinear wave are identified. In the weak magnetic field, the energy of beam-excited plasma waves at the nonlinear stage of beam-plasma interaction goes predominantly to the short-wavelength upper-hybrid waves propagating parallel to the magnetic field, whereas in the strong magnetic field, the spectral energy is transferred to the electrostatic whistlers with oblique propagation. [ABSTRACT FROM AUTHOR]

The power of second harmonic electromagnetic emission is calculated for the case when strong plasma turbulence is excited by a powerful electron beam in a magnetized plasma. It is shown that the simple analytical model of strong plasma turbulence with the assumption of a constant pump power is able to explain experimentally observed bursts of electromagnetic radiation as a consequence of separate collapse events. It is also found that the electromagnetic emission power calculated for three-wave interaction processes occurring in the long-wavelength part of turbulent spectrum is in order-of-magnitude agreement with experimental results. [ABSTRACT FROM AUTHOR]

Mode hybridization is a unique way to manipulate the mode inside a fixed cavity or at interface. For example, Tamm plasmon-polariton at solid interface can be spectrally shifted without tuning the interface. Experimental implementation of tunable hybrid Tamm-microcavity modes is reported. The hybrid modes are excited in a one-dimensional photonic crystal bounded with a gold layer by attaching a nematic liquid crystal microcavity. Coupling between Tamm plasmon-polariton and microcavity modes leads to repulsion of their dispersion curves controlled by the refractive index of a liquid crystal and the polarization of incident light. Effective tuning of hybrid modes through heating or applying an external electric field to the liquid crystal layer is demonstrated. The experimentally measured strength coupling value between Tamm and microcavity modes was 20.7 meV. [ABSTRACT FROM AUTHOR]

The development and nonlinear saturation of two-stream instability of a warm nonrelativistic electron beam in a cold plasma are investigated numerically in the framework of a one-dimensional model. It is shown that, for a sufficiently large velocity spread of the electron beam, instability develops and saturates according to a universal law, the wave phase velocity remains the same in the saturation stage, and the maximum field is somewhat lower than that predicted by classical estimates and depends in a different way on the growth rate. The damping of plasma oscillations not only changes the instability growth rate, but also substantially decreases the maximum wave field. [ABSTRACT FROM AUTHOR]

In 1985 Fridriech and Wintgen proposed a mechanism for bound states in the continuum based on full destructive interference of two resonances which can be easily applied to the two- and three-dimensional wave systems. Here we explicitly show that this mechanism can be realized in one-dimensional quantum potential well, owing to destructive interference of electron paths with different spin in tilted magnetic field. Due to one-by-one correspondence between the spin of the electron and the polarization state of light, we have found numerous bound states in the continuum in the one-dimensional photonic system and experimentally confirmed them. The experimental set-up consists of the one-dimensional photonic crystal conjugated with a liquid-crystalline anisotropic defect layer and covered by metal film. Bound states in the continuum have recently found application to sensing, lasing and optoelectronics, but have not been realised in 1D. Here, destructive interference of electron spin in a tilted magnetic field is shown to give rise to bound states in the continuum of a 1D layered photonic crystal. [ABSTRACT FROM AUTHOR]

The power of electromagnetic emission near the plasma frequency during collective electron beam-plasma interaction is found to be significantly increased in a plasma with preformed large-amplitude density perturbations. Laboratory experiments at the GOL-PET facility show that injection of a kiloampere relativistic electron beam into a magnetized plasma with strong radial density gradients is accompanied with an order of magnitude more intense generation of sub-millimeter waves than in the case of smooth density profile. As a possible mechanism for the enhanced generation of the longitudinal radiation flux observed in these experiments, we discuss the direct beam pumping of longitudinally propagating electromagnetic plasma modes due to their coupling with the Doppler shifted beam branch in the presence of oblique modulation of plasma density. [ABSTRACT FROM AUTHOR]