Negative refraction in one-dimensional plasma photonic crystals

We have theoretically explored the negative refraction (NR) in one-dimensional plasma photonic crystals (PCs) consisting of plasma and dielectric materials. By using the transfer matrix method and Bloch theorem, we have studied the group velocity and we have obtained the NR in plasma PCs with the help of the group velocity. The results show that plasma PCs can also exhibit the NR although they have a periodically modulated positive permittivity ? and permeability μ. It is also shown that the NR in plasma PCs exhibits difference behaviour in different frequency regions, ω < ω_p and ω > ω_p, respectively. The parameter dependence of the effects is also examined and discussed.     

Oscillating two-stream instability of beat waves in a hot magnetized plasma

It is shown that an electrostatic electron plasma beat wave is efficiently unstable for a low-frequency and short-wave-length purely growing perturbation (ω, k), i.e. an oscillating two-stream instability in a transversely magnetized hot plasma. The nonlinear response of electrons and ions with strong finite Larmor radius effects has been obtained by solving the Vlasov equation expressed in the guiding-center coordinates. The effect of ion dynamics has been found to play a vital role around ω ∼ ω_ci, where ω_ci is the ion-cyclotron frequency. For typical plasma parameters, it is found that the maximum growth rate of the instability is about two orders higher when ion motion is taken into account in addition to the electron dynamics.     

Self-focusing of electromagnetic waves in a magnetoplasma

The steady state self-focusing of a Gaussian electromagnetic beam in a magneto-plasma has been studied. On a short time scale, a non-linearity in the dielectric constant of a plasma appears due to the ponderomotive force. This force in the case of the extraordinary mode has opposite signs forω>ω _c andω<ω _c, whereω _c is the electron cyclotron frequency. The self-focusing due to this effect is predicted at frequencies except forω _c /2<ω<ω _c . The focusing of the ordinary mode is adversely affected by the magnetic field. On a larger time scale, the non-uniform heating of electrons by the beam and the resulting redistribution of the electron density is a source of non-linearity. This non-local non-linearity is several orders of magnitude higher than the ponderomotive non-linearity. We predict self-focusing of the extraordinary mode only above the gyroresonance (ω>ω _c ), while the ordinary mode can be focused at all frequencies.     

Excitation by light ofω + andω − surface plasma waves in thin metal layers

Calculations with the extended Fresnel formulae show, thatω ₊ andω _? surface plasma waves can be excited by light, using the following optical arrangement: The metal foil is embedded between two dielectric layers of low index of refraction and equal thickness. Both sides of this 3-layer packet are in optical contact with a high index prism. Total reflection is broken byω ₊ andω _? resonances in reflectivity, transmission and absorption. Theω ₊ resonance is mainly transmissive, (transmission through a 800 Å thick silver foil greater than 50% at a wavelength of 5,461 Å) theω _? resonance is mainly absorptive. The polarization of the transmitted light exceeds 99%-theω ₊ resonance is proposed as a principle for a new optical polarizer.     

Directed transport of modulated structures in the Frenkel–Kontorova model with a pulsating coupling

We study the directed transport of commensurate and incommensurate modulated phases of the Frenkel–Kontorova model by (parametric driving) periodic pulsed variation of the nearest-neighbor coupling in the dissipative limit of the dynamics. We obtain that a directed current flow appears as the amplitude of the pulsating coupling C increases above a threshold coupling C_th. This threshold coupling depends on the average interspacing ω between the oscillators displaying singularities as the system becomes commensurable with the underlying lattice. By making use of the discommensuration theory of modulated phases we obtain that the dependence of the directed current on ω is a piecewise linear function with integer slope. Numerical results confirm these predictions.     

Microwave heating of electrons of a dense plasma column at frequencies higher than electron cyclotron frequency

In the overdense collisionless plasma column inserted through the narrow sides of a rectangular waveguide, the excited electron cyclotron harmonic waves (CHWs) are studied by means of two movable probes and a phase interferometer in the range of parameters of 2 >ω/ω _ce >1; 0·5 < (ω _pe /ω)² < 15. Two kinds of CH waves have been found in the dipole mode:

1. Stable backward CH waves with the phase velocity in the direction from the axis to the periphery.
2. Unstable backward CH waves with the phase velocity in the opposite direction.

From the correlation measurements and amplitude distribution of the CH waves at the applied frequency and its second harmonic frequency it has been found that in the range of 2 >ω/ω _ce > >1·5 efficient nonlinear resonant interaction of CH waves takes place. The position of the loci of resonant interaction inside the plasma column has been found both experimentally and by a simple new graphical procedure for the resonant conditions of the formω ₂=2ω ₁; k₂=2¦k₁¦. In absence of this condition, no effective generation of the second harmonic frequency has been found. The resonant interaction of CHWs atω/ω _ce =1·85 is the cause of self-trapping of CH waves between the zones of resonant interaction in radial direction and of the anomalous heating rate of electrons.     

High frequency Brillouin scattering in metals and gaseous plasmas

Spontaneous and stimulated Brillouin scattering are studied in metals and gaseous plasmas, for an incident laser frequencyω ₁ greater than the corresponding plasma frequencyω _plin the medium. The calculation of threshold powers for the stimulated scattering in aluminium metal and non-degenerate Al-plasmas shows that their values become quite small asω ₁ approachesω _plFor the case of backward wave scattering we also estimate the critical power above which a temporal instability sets in such media. It is argued that this instability may be one of the factors for anomalously large absorption of high power laser beams in laser-induced plasmas.     

Effects of competition between the anisotropy and the spin quantum number on the magnon energy gap in a four-layer ferromagnetic superlattice

The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the spin quantum number. A special attention is also paid on the effects of the symmetry of the system. It is found that three modulated energy gaps exist in the magnon energy band along K_x direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The zero energy gap Δω₂₃ correlates with the conditions between anisotropy constants, D₁+D₃=D₂+D₄ and D₁=D₃ (or D₂=D₄), while the disappearance of the magnon energy gaps Δω₁₂ and Δω₃₄ corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Δω₁₂, Δω₂₃ and Δω₃₄ become larger. There is a competition effect of the anisotropy and the spin quantum number on the magnon energy gaps Δω₁₂ and Δω₂₃. When the symmetry of the system is higher, the competition can achieve a balance to cause the zero energy gap.     

New acceleration mechanism of electrons by an electromagnetic wave in a weakly magnetized plasma

Acceleration of electrons by an electromagnetic wave has been observed in a weakly magnetized (ω_ce/ω₀ ? 10^?2) inhomogeneous plasma. This acceleration is interpreted as a V_p × B₀ acceleration, which is a new concept for heating or accelerating electrons very efficiently to high energy.     

Surface-plasmon-polariton dispersion of semiconductors with depletion layers

For a sample with plasma frequency varying exponentially from ω_ps at the surface to a larger value ω_pb in the bulk, and moderate damping, we find, contrary to other calculations, that the long wavelength surface plasmon dispersion has a single branch that is reentrant at ω = ω_ps.     

Decay instability of plasma in crossed fields

In this paper it is shown that in plasma placed in crossed electric and magnetic fields, oscillations are excited with the frequency close to the drift frequencyω ₀ =k _? υ _? . Decay of the oscillations into two other oscillations, for which the selection rulesω ₀ =ω ₂ ?ω ₁ andm ₀=m ₂?m ₁ hold, where the frequencyω ₁ is close to the Langmuir frequency of ions, was observed.     

Molecular beam reactive scattering of Br2 from Pd(111) using an electrochemical effusive source

A computer-controlled modulated molecular beam source is used to investigate the kinetics of the surface reactions which occur when bromine is reactively scattered by Pd(111). The reaction products are atomic bromine and molecular bromine: the latter species arises from an adatom recombination process and gives rise to a product vector modulated at twice the frequency of the incident beam (2ω.) By making suitable measurements of the temperature dependence of the product vector phase shifts at ω and 2ω, the four kinetic parameters which characterise the first-order and second-order rate processes are obtained. These are: A₁ = 2.5×10⁹ s^?1, E₁ = 177 kJ mol^?1, A₂ = 3.6×10^?10 m² s^?1, E₂ = 131 kJ mol^?1. The significance of these values is discussed in terms of the properties of the transition state to desorption.     

Plasmons in semiconductors and insulators: A simple formula

Based on the dielectric function of an excitonic system, a simple model dielectric function is constructed. The high energy zero of this function yields the plasma frequency, and is given by: (hω_x)² = (hω_f)² + E_x² where ω_f is the free electron plasma frequency and E_x the lowest exciton energy. It is argued that this formula is valid for both, Frenkel and Wannier excitons, and comparison is made with experiments on a variety of crystals, ranging from InSb to Ar. In all cases, surprisingly good agreement is found.     

Propagation regimes of intense circularly polarized laser beam in magnetoactive plasma

This paper presents an analytical and numerical investigation of an intense circularly polarized wave propagating along the static magnetic field parallel to oscillating magnetic field in magnetoactive plasma. In the relativistic regime such a magnetic field is created by pulse itself. The authors have studied different regimes of propagation with relativistic electron mass effect for magnetized plasma. An appropriate expression for dielectric tensor in relativistic magnetoactive plasma has been evaluated under paraxial theory. Two modes of propagation as extraordinary and ordinary exist; because of the relativistic effect, ultra-strong magnetic fields are generated which significantly influence the propagation of laser beam in plasma. The nature of propagation is characterized through the critical-divider curves in the normalized beam width with power plane For given values of normalized density (ω_p/ω) and magnetic field (ω_c/ω) the regions are namely steady divergence (SD), oscillatory divergence (OD) and self-focusing (SF). Numerical computations are performed for typical parameters of relativistic laser-plasma interaction: magnetic field B = 10-100 MG; intensity I = 10¹⁶ to 10²⁰ W/cm²; laser frequency ω = 1.1 × 10¹⁵ s⁻¹; cyclotron frequency ω_c = 1.7 × 10¹³ s⁻¹; electron density n_e = 2.18 × 10²⁰ cm⁻³. From the calculations, we confirm that a circularly polarized wave can propagate in different regimes for both the modes, and explicitly indicating enhancement in wave propagation, beam focusing/self-guiding and penetration of E-mode in presence of magnetic field.     

Dynamic stabilization of the helicalm=1 instability in a linear screw pinch

Dynamic stabilization of the helicalm=1 instability was studied in the linear high-β screw pinch ISAR III (T _i ≈50 to 500eV;n _e ≈5·10¹⁶ cm^?3; β≧0.5). The experimentally determined growth rates ω _i (0.5 to 3·10⁶ s^?1) and wavelengths (100 to 200 cm) of these modes are about the same as in a toroidal screw pinch and both agree well with theory. Two methods of dynamic stabilization were investigated. In both cases the stabilizing effects were better than expected from existing theory. In the first method an axially uniform oscillating field \(\tilde B_{zo} \) ·sin (ω _s t) was superposed on the quasi-steadyB _zo field (ω _s >ω _i ). Them=1 mode is stabilized and a stabilization condition \(\tilde B_{zo} /B_{zo} \gtrsim 2\omega _i /\omega _s \) holds. This stabilizing effect is very likely caused by inertial forces produced by enforcedm=0,k=0 oscillations of the plasma column. When working in resonance with the natural plasma oscillations, it is easier to satisfy the above condition. In the second method oscillating currents \(\tilde I_{zo} \) · sin (ω _s t) were added to the axial plasma currentI _zo to study the stabilization by dynamic shear (ω _s >ω _i ). Magnetic probe measurements showed that the \(\tilde I_z \) flows in the dilute plasma outside the dense plasma column. The measured skin depths and resistivities are larger than those expected from classical theory. Nevertheless, a reduction of the growth of them=1 mode occurred which was larger the more closely \(\tilde I_z \) flowed alongside the plasma column, giving a stabilization condition \(\tilde I_{zo} /I_{zo} > \omega _s /(5\omega _i )\) .     

Parametric excitation of relativistic plasma oscillations by strong electromagnetic waves

Parametric interaction of strong waves ($\text{?=}\text{eE}{}_{\mathrm{<mtext>o</mtext>}}\text{m}{}_{\mathrm{<mtext>e</mtext>}}\text{cω}{}_{\mathrm{<mtext>o</mtext>}}\text{～ 1}$) with a cold, two-fluid (ion and electron) plasma is studied in the limits of high frequency (ω_o?ω_Le) and resonance (ω_o ≈ ω_Le). Unstable oscillations of both electrons and ions are found in the resonance limit.     

Optical effects caused by coincidence between the energies of the plasma oscillations and the band-to-band transition in bismuth crystals doped with an acceptor impurity

The energy of plasma oscillations of free charge carriers in bismuth crystals ?ω_p can be qual to the band gap at the L point of the Brillouin zone E _gL as a result of doping with an acceptor impurity. Variation in the edge shape and splitting of the minimum in the plasma reflection are observed in experimental studies of reflection under normal incidence of radiation on the crystal. An analysis of the totality of available experimental data shows that the above special features are caused by interaction of elementary excitations (such as the plasma oscillations) with band-to-band transitions. It became possible for the first time to ascertain the composition of the bismuth crystals for which the condition ?ω_p=E _gL is satisfied and observe the variation in the characteristics of the plasma oscillations of free charge carriers, which occurs as a result of electron-plasmon interaction.     

Plasmaresonanzemission und Plasmaresonanzabsorption an dünnen Kaliumschichten

Optical transmission and emission spectra in the region of the plasma frequencyω _p were measured on thin potassium films evaporated on sapphire substrates of various temperatures. For the foils condensed at a temperatures of the substrateT _a T _a >?165 °C transmission spectra were observed which transmission minima are displaced to frequencies less thanω _p . Plasma resonance emission was observed from these foils. Comparison with calculated emission spectra gives an approximate agreement.     

Propagation of electromagnetic waves in hot magnetoactive plasma

The paper derives the general form of the tensor of dielectric permittivity? _ij(ω,k), Eq. (15), of non-relativistic hot magnetoactive collisionless plasma taking into consideration the influence of spatial dispersion. The general form of the tensor? _ij(ω,k) is used to express the tensorε _ij(ω,k) in the region of weak and strong spatial dispersion and in some special cases. A general dispersion equation (30) is derived and an analysis is made of the waves propagating in hot magnetoactive plasma. The expressions derived are used to investigate the damping of a right-handed circularly polarized wave propagating in hot magnetoactive plasma in the direction of the magnetic field.     

Die transversale,negative, differentielle Leitfähigkeit von n-Germanium: Zwei 2-Tal-Modelle ihrer statischen und dynamischen Eigenschaften

Taking into account two of the four 111-energy minima of the Ge-conduction band, expressions for the field and frequency dependent transverse differential conductivityσ _yy(ω, E _x) have been derived. Forω=0, one obtains the static properties, especially information concerning the critical fieldsE _xc defined byσ _yy(0,E _xc)=0. Forω≠0, the plasma frequenciesω _p have been calculated fromσ _yy(ω, E _x). One of these goes to zero forE _x→E _xc (soft mode). The optical quantities: refractive index, extinction and reflection coefficient have also been calculated. They show anomalies in the regionE _x=E _xc. To evaluate the equations quantitatively, the intervalley and the momentum scattering rate have been derived in the last part of this work using known distribution functions.