Nonlinear parametric interactions in ion-implanted semiconductor plasmas having strain-dependent dielectric constants

We report nonlinear parametric interactions using a hydrodynamic model of ion-implanted semiconductor plasmas having strain-dependent dielectric constants(SDDC). High-dielectric-constant materials are technologically important because of their nonlinear properties. We find that the third-order susceptibility varies in the range 10~(-14)~(–10)~(-12)m~2·V~(-2) for ion-implanted semiconductor plasmas, which is in good agreement with previous results. It is found that the presence of SDDC in ion-implanted semiconductor plasma modifies the characteristic properties of the material.     

激光驱动材料动态压缩技术

激光驱动动态压缩实验是极端高压高密度研究的主要途径,在多个学科领域具有重要意义,包括地球行星科学,材料科学以及惯性约束聚变,有助于认识极端条件下的材料特性并拓展其在各学科的应用。近年来激光驱动压缩技术在激光装置、激光等离子体、制靶和诊断技术的同步提升下取得了突破性的进展,与其他极端条件实验平台相比,其斜波压缩、复杂路径、衰减冲击等新型加载路径得到快速发展,微介观诊断技术和宏观诊断技术相结合,具有明确的超高压、高温、高应变率以及高同步精度等技术特色。从激光驱动材料压缩的热力学路径、激光驱动的机制与特色、激光驱动实验技术、材料极端压缩物理进展等方面介绍激光驱动实验和理论方面的进展。     

Velocity gradient driven flute instabilities in plasmas

The effect of velocity gradient across the magnetic field on the low frequency flute modes is examined in detail, using the normal mode analysis. It is shown that some new type of instabilities driven primarily by the velocitygradient arise and these excited modes eventually attain the convective saturation. The onset of plasma turbulence due to these instabilities may possibly be one of the major contributors for anomalous heating process and enhanced plasma resistivity.     

Laser generation of convergent acoustic waves for materials inspection

A laser technique for generating convergent acoustic waves is described. The optically probed Rayleigh wave in the centre of convergence shows an amplification factor of the order of 20 with respect to a collimated surface wave. Applications to the ultrasonic characterization of layered materials and to crack detection are described.     

Colossal dielectric constants in transition-metal oxides

Many transition-metal oxides show very large (“colossal”) magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation. In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu₃Ti₄O₁₂ and related systems, which is today’s most investigated material with colossal dielectric constant. Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La_2−xSr_xNiO₄ where electronic phase separation may play a role in the generation of a colossal dielectric constant.     

Laser interaction with a dielectric block

Some optical experiments provide the easiest way to test quantum mechanical predictions. Such a situation applies to a laser beam traversing a dielectric structure. The dielectric structure mirroring quantum mechanical potentials. The simplest of these, studied in this paper, involves a single dielectric block. We exhibit both by analytic and numerical calculations explicit examples of total coherence and total incoherence phenomena. Which case appears depends upon the angle of incidence of the laser beam and/or the dimensions of beam vs. block width. Unlike our previous studies our calculations here are three-dimensional, although, with suitable approximations, somewhat simpler planar expressions can be derived.     

Colossal dielectric constants: A common phenomenon in CaCu3Ti4O12 related materials

In the present work we demonstrate that in addition to the well-known colossal-dielectric-constant material CaCu₃Ti₄O₁₂ various members of the series Ln_2/3Cu₃Ti₄O₁₂ with Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm also exhibit giant values of the dielectric constant. Just as CaCu₃Ti₄O₁₂, all these materials show a Maxwell–Wagner type relaxation process. For the best material, Pr_2/3Cu₃Ti₄O₁₂, we provide a detailed investigation of its dielectric properties in a broad frequency range up to 1 GHz. Polarization at internal barriers, most likely grain boundaries, seems to be the reason for the observed very high values of the dielectric constant. Taking into account the present results and those reported in the literature, we conclude that CaCu₃Ti₄O₁₂ is not exceptional at all and there seem to be various isostructural materials with similar dielectric properties.     

Laser pulse modulation instabilities in partially stripped plasma

The laser pulse modulation instabilities in partially stripped plasma were discussed based on the phase and group velocities of the laser pulse and the two processes that modulation instabilities excited. The excitation condition and growth rate of the modulation instability were obtained. It was found that the positive chirp and competition between normal and abnormal dispersions play important roles in the modulation instability. In the partially stripped plasma, the increased positive chirp enhances the modulation instability, and the dispersion competition reduces it.     

Correlation functions near instabilities in systems driven by parametric noise

For a quantum system weakly coupled to heat reservoirs, a statistical mechanical theory is developed in a formalism that dovetails perfectly with phenomenological thermodynamics. The present model is a modification of the many-reservoir model by Bergmann and Lebowitz. The method to be used here is based on the explicit introduction of external forces which bring about a deviation from equilibrium. These forces are assumed to arise from mechanical interaction with its surrounding which can be characterized thermodynamically. By an appropriate choice of reservoirs the Liouville-von Neumann equation is found to describe a heat conducting system. The nonequilibrium density matrices which describe such a system are found explicitly for some interesting cases. With these density matrices we obtain an expression for entropy production.     

Collision and recombination driven instabilities in variable charged dusty plasmas

The dust-acoustic instability driven by recombination of electrons and ions on the surface of charged and variably-charged dust grains as well as by collisions in dusty plasmas with significant pressure of background neutrals have been theoretically investigated. The recombination driven instability is shown to be dominant in the long wavelength regime even in the presence of dust-neutral and ion-neutral collisions, while in the shorter wavelength regime, the dust-neutral collision is found to play a major role. In an earlier research work, the dust-neutral collision was neglected in comparison to the effect due to the recombination for estimating the dust-acoustic instability; later the other report shows that the recombination effect is negligible in the presence of dust-neutral collisions. In line of this present situation our investigation revealed that the recombination is more important than dust-neutral collisions in laboratory plasma and fusion plasma, while the dust-neutral collision frequency is dominant in the interstellar plasmas. The effects of ion and dust densities and ion streaming on the recombination and collision driven mode in parameter regimes relevant for many experimental studies on dusty plasmas have also been calculated.     

Ion beam driven instabilities in unmagnetized and strongly magnetized plasmas

In this paper, the dissipative instabilities in the interaction of an ion beam with unmagnetized and strongly magnetized plasmas are investigated. In both cases, relevant dispersion equations of high-frequency and ion acoustic waves are obtained. In addition, the resonance frequencies and growth rates of the instabilities are derived. It is shown that the thermal motion of charged particles has positive effects on the resonance frequency but its influence on the growth rate of an instability depends on the plasma conditions. Although in all cases the collisions are found to have a stabilizing effect, it is shown that the dominant type of collisions (electron-neutral or ion-neutral collisions) depends on the frequency range. It is also indicated that the resonance frequency and the growth rate of an instability in the unmagnetized plasma is higher than in the strongly magnetized plasma for non-zero propagation angles.     

Light-induced instabilities driven by competing helical patterns in long-pitch cholesterics

We study theoretically the dynamical reorientation phenomena when a long-pitch cholesteric liquid-crystal film with homeotropic alignment is illuminated by a circularly polarized lightwave. In the present case, the natural cholesteric pitch is of the order of (or larger than) the film thickness. The helical cholesteric structure is thus frustrated by the boundary conditions without illumination. However, above a light intensity threshold reorientation occurs and the bifurcation scenario depends strongly on the natural cholesteric pitch. Recalling that a long-pitch cholesteric is achieved in practice by adding a small amount of chiral agents in a nematic liquid crystal, the observed dynamics can be viewed as the result of the competition between intrinsic and extrinsic unidimensional helical patterns. The intrinsic part consists of the helical deformations induced by the chirality of the dopant, whereas the extrinsic part is related to the chirality induced by the optical field through the non-uniform angular momentum transfer of light to a nematic. The all-optical analog in the case of a pure nematic (without chiral dopant), is also discussed.     

Gravity driven instabilities in miscible non-Newtonian fluid displacements in porous media

Gravity driven instabilities in model porous packings of 1 mm diameter spheres are studied by comparing the broadening of the displacement front between fluids of slightly different densities in stable and unstable configurations. Water, water–glycerol and water–polymer solutions are used to vary independently viscosity and molecular diffusion and study the influence of shear-thinning properties. Both injected and displaced solutions are identical but for a different concentration of NaNO₃ salt used as an ionic tracer and to introduce the density contrast. Dispersivity in stable configuration increases with polymer concentration – as already reported for double porosity packings of porous grains. Gravity-induced instabilities are shown to develop below a same threshold Péclet number Pe for water and water–glycerol solutions of different viscosities and result in considerable increases of the dispersivity. Measured threshold Pe values decrease markedly on the contrary with polymer concentration. The quantitative analysis demonstrates that the development of the instabilities is controlled by viscosity through a characteristic gravity number G (ratio between hydrostatic and viscous pressure gradients). A single threshold value of G accounts for results obtained on Newtonian and non-Newtonian solutions.     

Laser probing of anisotropic ultrathin dielectric films on absorbing materials via differential reflection characteristics

The reflection from an ultrathin anisotropic film on an isotropic absorbing substrate is investigated in the long-wavelength limit. The analytical expressions for the differential reflection characteristics of s- and p-polarized electromagnetic plane waves are obtained. All analytical results are correlated with the numerical solution of the reflection problem on the basis of rigorous electromagnetic theory for anisotropic medium. The possibilities of using the obtained approximate formulas for resolving the inverse problem for ultrathin anisotropic dielectric films upon absorbing substrates are discussed.     

Cloaking an acoustic sensor with single-negative materials

In this review, a brief introduction is given to the development of acoustic superlens cloaks that allow the cloaked object to receive signals while its presence is not sensed by the surrounding, which can be regarded as “cloaking an acoustic sensor”. Remarkably, the designed cloak consists of single-negative materials with parameters independent of the background medium or the sensor system, which is proven to be a magnifying superlens. This has facilitated significantly the design and fabrication of acoustic cloaks that generally require double-negative materials with customized parameters. Such innovative design has then been simplified further as a multi-layered structure comprising of two alternately arranged complementary media with homogeneous isotropic single-negative materials. Based on this, a scattering analyses method is developed for the numerical simulation of such multi-layered cloak structures, which may serve as an efficient approach for the investigation on such devices.     

The dielectric screening and magnetic instabilities in an interacting electron gas

The values of a parameter r_s are investigated, for which (a) the static dielectric function becomes negative, (b) the transition into the spinpolarized state takes place.     

Solar wind driven electrostatic instabilities with generalized (r,q) distribution function

Using Boltzmann–Vlasov kinetic model, a currentless ion acoustic instability driven by stream of solar wind plasma is studied in a non‐thermal distributed electrons and ions. The non‐thermal distribution considered here is the generalized distribution which has low energetic flat‐top and velocity power law tail at higher energies. The instability threshold is found to be affected and depends upon the spectral indices r and q . It is found that the growth rate increases with the decrease in the value of r and increase with q . Moreover, such kinetic instability has also been discussed for three species electron–ion–dust plasma using the generalized (r, q) distribution function. Such case is of interest when the solar wind is streaming through the cometary plasma in the presence of interstellar dust and excites electrostatic instabilities. The dispersion properties and growth rates for ion‐acoustic and dust‐acoustic mode are calculated analytically and plotted for different values of the spectral indices r and q .