Characterization of pulsed laser generated plasma through its perturbation in an electric field

The perturbation produced by pulsed laser generated discharge in an electric field is studied as a tool for breakdown characterization. A focused high-power pulsed laser induces a discharge in air or in a solid target, that is placed between the plates of a planar charged capacitor. The induced discharge generates a temporal redistribution of the electrical charges on the plates that can be easily measured by a resistor connected to the ground plate. This signal depends on the energy used to generate the breakdown, the capacitor applied voltage, and the distance between the plates. In this work, we show that this signal can be readily used to optimize the relevant parameters involved in laser-induced breakdown spectroscopy in gases and in solid targets.     

Nonclassicality generated by propagation of atoms through a cavity field

We successively pass two V-type three-level atoms through a single-mode cavity field. Considering the field to be initially in a classical state, we evaluate various statistical properties such as the quasiprobability Q function, Wigner distribution, Mandel?s Q parameter and normal squeezing of the resulted field. We notice that the sequential crossing of atoms induces nonclassicality into the character of a pure classical state (coherent field). The initial thermal field shows sub-Poissonian as well as squeezing property after interacting with the V atoms.     

也谈均匀带电细圆环的电场分布

用Mathematica研究均匀带电细圆环的电场的空间分布,准确地绘制出电场强度量值的分布图和电场方向的分布图,并纠正了最近文献中一幅场强量值分布图的失误.     

Mass dependence of the electric field gradient generated by impurities in cubic lattices

The variation of the electric field gradient generated by substitutional impurities in cubic lattices is calculated at fixed temperature as a function of the impurity mass and a good agreement with previous experimental results is found.     

Boundary element numerical method for the electric field generated by oblique multi-needle electrodes

According to the electric potential of oblique multi-needle electrodes (OMNE) in biological tissue, the discrete equations based on the indetermination linear current density were established by the boundary element integral equations (BEIE). The non-uniform distribution of the current flowing from multi-needle electrodes to conductive biological tissues was imaged by solving a set of linear equations. Then, the electric field and potential generated by OMNE in biological tissues at any point may be determined through the boundary element method (BEM). The time of program running and stability of computing method are examined by an example. It demonstrates that the algorithm possesses a quick speed and the steady computed results. It means that this method has an important referenced significance for computing the field and the potential generated by OMNE in bio-tissue, which is a fast, effective and accurate computing method. Supported by the Natural Science Foundation of Beijing (Grant No. 1083011), the National Natural Science Foundation of China (Grant No. 10705049), and the Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality     

dc Magnetic field generated by an electric dipole antenna in an anisotropic plasma

dc magnetization generated by an ac electric dipole in a magnetized plasma is considered. The main result is the expression of the induced dc magnetic field in a system with axial symmetry. It has a general form valid for any ac source with the same symmetry.     

On the frequency of oscillations in the pair plasma generated by a strong electric field

We study the frequency of the plasma oscillations of electron–positron pairs created by the vacuum polarization in a uniform electric field with strength E   in the range 0.2Ec<E<10Ec$0.2E_c<E<10E_c$. Following the approach adopted in Ruffini, et al. (2007) [1] we work out one second order ordinary differential equation for a variable related to the velocity from which we can recover the classical plasma oscillation equation when E→0$E\to 0$. Thereby, we focus our attention on its evolution in time studying how this oscillation frequency approaches the plasma frequency. The time-scale needed to approach to the plasma frequency and the power spectrum of these oscillations are computed. The characteristic frequency of the power spectrum is determined uniquely from the initial value of the electric field strength. The effects of plasma degeneracy and pair annihilation are discussed.     

Improved fictitious charge method for calculations of electric potential and field generated by point-to-plane electrodes

In the framework of standard tip-to-plane electrode geometry favorable to corona streamer discharge development at atmospheric pressure, this work is devoted to the improvement of fictitious charge method for calculations of electric potential and field repartition when the tip is powered by a DC voltage. It is in fact dedicated to implement the image charge method (generally used in plane-to-plane electrodes) in the case of a point-to-plane geometry. The numerical method is based on the solution an open system of n equations with m unknowns (n >> m) where m is the number of fictitious charges and n the number of contours at the surface of the tip electrode defining the boundary conditions. This numerical technique can accurately interpolate the shape of the electrode tip whatever its geometry and hence allows us to accurately calculate the electric potential and field even at a position very close to the electrode. It is noteworthy that the solution of such open system of equations cannot be obtained from conventional techniques (Cramer, Gauss, matrix inversion, etc.). We used the method of least squares which enables us to close the equation systems and to find the optimal solution fulfilling all the required boundary conditions. The present method is therefore based on the coupling between the conventional method of fictitious charges using image charge method and the optimization by the Least Squares Method. The results of simulation show that the punctual fictitious charges have given the most accurate results when the electrode has symmetry of revolution like the present geometry of a pen shape anode cylinder ended by a sharp tip set in front of cathode plane.     

线电荷椭圆环中心轴线电场分布

运用场的叠加原理和椭圆积分的理论和方法,导出了线电荷椭圆环中心轴线场强分布的解析表达式,进行了有关的讨论,指出线电荷椭圆环中心轴线场分布具有的重要特性.     

用磁标势求解稳恒电流磁场边值问题

介绍了用磁标势求解稳恒电流磁场边值问题方法、步骤。给出了典型的熊产生均匀磁场的应用实例。     

Computer generated hologram from full-parallax 3D image data captured by scanning vertical camera array (Invited Paper)

Full-parallax light-field is captured by a small-scale 3D image scanning system and applied to holographic display. A vertical camera array is scanned horizontally to capture full-parallax imagery, and the vertical views between cameras are interpolated by depth image-based rendering technique. An improved technique for depth estimation reduces the estimation error and high-density light-field is obtained. The captured data is employed for the calculation of computer hologram using ray-sampling plane. This technique enables high-resolution display even in deep 3D scene although a hologram is calculated from ray information, and thus it makes use of the important advantage of holographic 3D display.     

Propagation effects of a fractal rough ocean surface on the vertical electric field generated by lightning return strokes

Based on an improved two-dimension (2D) fractal model of rough ocean surface, the propagation effects of the rough ocean surface on the vertical electric fields generated by lightning return strokes are analyzed. The results show that the rough ocean surface has much effect on the electric field derivatives, but has no or little effect on the field peaks. The frequency above 10 MHz is attenuated significantly by the rough ocean surface, and the rapid attenuation of frequency above 10 MHz in the experimentally obtained spectrum may be taken into account the errors introduced by the roughness of the ocean surface.     

An escape of fast electrons from a plasma cluster in subcritical electric field

A behaviour of electrons with high initial thermal velocities in plasma clusters is discussed in the paper. These electrons from the tail of the Maxwell velocity distribution can be accelerated into considerable energies by means of an external electric field. Both numerical and analytical estimates of the energy of the escaping electrons and an estimate of the total energy transferred by the electrons from the cluster are treated in the paper. The calculations are performed for a situation usual in coaxial and rail accelerators of the plasma clusters.     

Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.     

High-order reflections from a cholesteric helix induced by an electric field

Using a modulation spectroscopy method the second-order selective reflection spectrum, induced by an electric field applied to the planar cholesteric texture, was measured. The third- and fourth-order reflections have not been found.     

Destabilizing effect of a surface electric field generated by ionic adsorption on the molecular orientation of nematic liquid crystals

The destabilizing effect of a surface electric field, produced by selective ionic adsorption, on the molecular orientation of a nematic-liquid-crystal sample is analyzed for a cell in the shape of a slab of thickness d. The electric-field distribution considered in the analysis is the one obtained in the limit in which essentially all the positive ions are adsorbed. Because of the coupling of this surface field with the nematic director, the surface anchoring energy depends on the thickness of the sample as well as on the adsorption energy characterizing the surfaces. A relation connecting the threshold field for the destabilization of the homeotropic pattern to the adsorption energy and to the thickness of the sample is established in closed form, after solving a set of two coupled non-linear equations determining the electric-field distribution across the sample. It is shown that the values of surface electric field generated by adsorbed ions that can lead to a destabilization of the homeotropic alignment can be attained by real samples.     

在时谐电磁场中用矢量势A直接表达电场强度E的一个显式

根据麦克斯韦方程组和洛伦兹条件,对时谐变场e导出用矢量势A直接表达电场强度E的一个显式,并对它进行了讨论.     

Efficient extraction of hydrogen ions from high-velocity plasma bunches by a pulsed electric field

The systematized results are presented of an investigation of the process of the efficient extraction of ions, by a pulsed electric field, from the surface of a plasma moving at a velocity of 10⁴ m/sec under the conditions of small accelerating diodes. A mathematical model is analyzed of the propagation of a plasma bunch formed by a laser pulse (E _las<1 J) in a quasicylindrical diode system. The possibilities are considered of increasing the current of the extracted ions by utilizing the phenomenon of magnetic confinement of electrons, and diode systems with a transparent anode. The designs of small acceleration tubes for generating neutron pulses are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 65–74, April, 1996.     

The intensity of the field generated by a point source and reflected from a rough surface

This paper studies the intensity of the acoustic field generated by a point source above a rough surface with the Dirichlet or Neumann boundary conditions. The derived equations are valid for arbitrary distances between the source, receiver and rough surface, including the case when these distances are smaller than the correlation radius of the surface roughness. It is believed that the proposed method is an improvement of the more conventional approach, which is based on integration over individual areas of the rough surface and that is valid when the source, receiver, and surface are at large distances from each other. The main limitation in deriving the expressions for the acoustic field intensity is the condition that the mutual shadowing of the surface points is small, which is close to the small slope approximation for the rough surface profile. The derivation includes the limiting cases which lead to the traditional small perturbation method and Kirchhoff approximation.     

Characterizing individual scattering events by measuring the amplitude and phase of the electric field diffusing through a random medium

We describe observations of the amplitude and phase of an electric field diffusing through a three-dimensional random medium, using terahertz time-domain spectroscopy. These measurements are spatially resolved with a resolution smaller than the speckle spot size and temporally resolved with a resolution better than one optical cycle. By computing correlation functions between fields measured at different positions and with different temporal delays, it is possible to obtain information about individual scattering events experienced by the diffusing field. This represents a new method for characterizing a multiply scattered wave.