Calculation of the surface-wave excitation in multilayeredstructures

A novel rigorous analysis of the surface waves excited by a Hertzian dipole embedded in a multilayered structure is presented. A transmission-line resonator equivalent circuit is used to calculate the surface wave's electromagnetic field components. It is shown that the power carried by the surface waves is related to the energy stored in the resonator. An analytical method for the calculation of the stored energy is given. A simple algorithm iterating over the layers of the structure is derived to analytically calculate the surface wave's electromagnetic field components and the power carried by surface waves. The need of numerical integration or calculation of residues is omitted. This benefits a reduction in computation time and an improvement in accuracy and versatility of computer-aided design (CAD) programs. The presented method has been implemented in a microwave CAD program. Numerical results for planar antennas are presented     

Optical-fibre excitation by finite beams

Simple formulas are given for trapped-mode power excited by a spot of light illuminating an optical fibre. The results are used to discuss features of Gaussian-beam excitation.     

双光子共振激发的电离复合产生受激电子辐射

文中报道利用双光子共振激发锂原子到4s态,获得了多条受激电子辐射和相干辐射,同时观察到了高于4s能级的nd,ns态(n≥4)到2p态的跃迁,以及从连续态到3s态的辐射。     

Propagation and excitation of perturbations in electron beams with velocity shear

A theoretical investigation of the influence of a spatially varying drift velocity on the perturbations in magnetically focused electron beams is presented. The wave propagation on such beams, focused by infinite magnetic fields, is studied under the small-wave assumption. The dispersion relation for slow waves is derived and solved for different transversal boundary conditions. Two sets of infinitely many propagating modes are found in a beam with small velocity shear. In a beam with sufficiently large velocity shear only two eigenfunctions exist. Since it is not possible to match the two eigenfunctions on arbitrary longitudinal boundary conditions, additional solutions (which cannot be written in form of a plane wave) must exist. The excitation of perturbations by ideal grids is solved by introducing the Laplace transform analysis. Additional solutions are ascertained which lead to a spatial decay of the perturbations according to a power law z^-α. This damping, arising from the spatially varying drift velocity, is similar to the Landau damping in electron beams with velocity distribution. Such damping effects are of great practical importance in conjunction with noise reduction in traveling-wave tubes.     

Limitations on millimeter-wave power generation with spiraling electron beams

A study is made of the suitability of the interaction between a thin, solid, spiraling electron beam of 5-15-kV energy and a microwave cavity, for the purpose of generating watts of CW millimeter-wave power. The effect of finite energy spread in the electron beam is considered both theoretically and experimentally. Measured results are given for a prototype device operating at 9.4 GHz. Power outputs of 5 W and electronic efficiencies near 2 percent have been obtained. The data agree well with the theory, subject to some ambiguity in the energy-distribution parameters. The performance is strongly limited by the energy spread in the beam.     

Powerful electromagnetic millimeter-wave oscillations produced by stimulated scattering of microwave radiation by relativistic electron beams

The stimulated scattering of electromagnetic waves in microwave generators, in which a high-current electron beam excites either a backward wave (BWO) or a quasi-critical frequency wave (orotron) is investigated experimentally. The scattering occurs at the same electron beam and the high-frequency feedback is provided by the inhomogeneities of the electrodynamic system of the microwave generator itself. A power of several tens of megawatts has been achieved in the 3-mm range. The mode selection permitted to obtain single-mode scattering.     

On the edge mode in the theory of TM scattering by a strip or strip grating

Consider a plane wave incident on a perfectly conducting strip (or strip grating), and let the incident electric vector be parallel with the edges of the strip. If the edge mode is included among the basis functions, it is found this greatly improves the convergence of the moment-method solution. Numerical data are included for the reflection coefficient of the strip grating. To correct an error in the previous literature, the rigorous solution is tabulated for broadside backscatter from a single strip.     

Propagation characteristics of the TM01 surface-wave mode in dielectric-lined coaxial cables

Accurate calculations of the propagation coefficients of the TM01 surface-wave mode in coaxial cables with dielectric linings on the inner, outer or both conductors were carried out using a perturbation method, and were checked by solving the exact characteristic equations. The calculations show that the perturbation method yields very accurate results, and that the attenuation coefficients cannot be reduced below that of the quasi-TEM mode in the unlined cable.     

Powerful millimeter-wave generators based on the stimulated Cerenkov radiation of relativistic electron beams

Effective relativistic Cerenkoy generators of various types were studied experimentally: orotrons, surface wave oscillators, and Smith-Purcell free-electron masers that were first realized. Single-mode generation was obtained in multimode systems using electrodynamic and electron methods of mode selection. The power obtained in this regime was 100 MW at 8.6 mm with the efficiency 10%, 50 MW at 5.5 mm with the efficiency 5%, and 8 MW at 2.4 mm with the efficiency 3%. In a multimode regime the power of 0.5 MW was obtained at 0.9 mm. The study of the dependence of the generation power on the value of the focusing magnetic field revealed the presence of zones of cyclotron power absorption, that were earlier observed in centimeter-wave generators.     

Launching of the HE11 surface-wave mode on a dielectric rod

The fields excited by a point electric dipole situated on, but oriented perpendicularly to, the axis of an infinitely long dielectric rod are examined. A technique, which involves expressing the fields and the source in a Fourier integral in the z direction and a Fourier series in the ? direction in a cylindrical co-ordinate system (p, ? z), is adopted for the analysis. Only the dominant HE11 dipole modes are found to be excited. Some preliminary numerical results for the dispersion characteristics and the surface-wave power are presented.     

Computations for radiation and surface-wave losses in coplanarwaveguide bandpass filters

A new approach is developed to simulate both radiation and surface-wave losses in general coplanar waveguide (CPW) discontinuity structures. The newly derived formulas are concise, simple, and efficient for computation. Full-wave characterization of CPW filter structures are first accomplished by the mixed-potential integral equation and the method of moments. Given equivalent magnetic-current distributions on the apertures of a CPW, the matrix pencil approach is applied to extract the scattering parameters and the new formulas are employed to obtain the losses and far-field patterns of the space-wave radiation and surface wave. Simulation of the calculated radiation and surface-wave losses by field theory is found to be consistent to the total power loss determined from the scattering parameters by circuit theory, which verifies the correctness of our new expressions     

Heating of solid targets by electron beams

The heating of a solid material by a high-energy electron beam is discussed. The two-dimensional transient nonlinear heat equation has been solved by the finite element method, considering both the penetration of the beam into the target and its finite size. The importance of the temperature dependences of each of the material properties on melt time have been established. Results are presented for the time needed for the first melting of the target for Cu, AI, Si, GaAs, impinged by beams having energies and parameters covering a wide range of values. Also the regimes of validity of the one-dimensional heat equation are discussed.     

Influence of surface-wave excitation on efficiency of space-wave launching in microstrip disc antennas

The cavity model with magnetic side walls and dyadic Green's functions was used to study microstrip disc antennas. Curves of efficiency of space-wave launching and directivity as functions of the ratio of the dielectric thickness to the disc radius d/a are shown for two dielectrics: ?r=2.55 and 9.60. The results are useful for the design of these antennas.     

Short-wave radiation pattern emitted by a slab with a periodically modulated refractive index

Comments are made on the radiation patterns predicted in the literature for a slab with a c.w. periodically modulated refractive index. A microwave system is described which should, generate bands of discrete lines in a limited range of frequencies in the millimetre or far-infrared regions.     

Space-charge wavelengths in electron beams

The discrepancies between measured and calculated small-signal space-charge wavelengths are discussed. It is shown that conventional methods of calculation are inadequate, causing errors up to 40 percent in a typical case. It is demonstrated that these errors cannot be explained by beam scalloping action, and that they are most severe when a high-perveance beam is used at low voltages with a high magnetic field under conditions of low interception. Although these effects would not be noticed in klystrons with relatively short drift lengths, they may in many cases explain the critical variation of gain and efficiency with magnetic field. A more accurate method of calculating space-charge wavelengths is developed, and the effectiveness of this method is demonstrated by a comparison with measurements.     

Transverse electron-beam wave excitation by photoelectric mixing of laser beams

It is shown theoretically that, by photoelectric mixing of laser beams which are incident obliquely on to a photosurface, transverse electron-beam waves may be excited. It should thus be possible to construct transverse-field microwave phototubes for detecting amplitude-modulated laser signals.     

Noise reduction in electron beams

Direct measurements were made of the electron-beam noise parameters using a modified Currie-type gun. The noise parameters were measured as a function of the electric field in the vicinity of the cathode. The S parameter was found to be strongly influenced by this field in the Currie-type gun, but the parameterpi/sis relatively unaffected.     

调制电子束在空间等离子体中激发的电磁波辐射

当调制电子束入射进空间等离子体时,由于电子束本征电磁场在非均匀等离子体中的散射(渡越辐射transition radiation)或者电子束的纵向约束性可以产生电磁波辐射.基于这两种辐射机制,研究了半无界调制电子束从航天器入射进平面分层各向同性非均匀空间等离子体产生的电磁波辐射.结果表明,由背景等离子体非均匀性产生的电磁波辐射强度高于由束的纵向约束性引起的辐射强度通过对电子束的适当调制,可以满足辐射电磁波在局部等离子体谐振区域的共振条件,从而增大辐射强度.研究结果可用于对主动空间等离子体试验数据的分析.     

Regrowth of heavy-ion implantation damage by electron beams

Electron transparent Si, Ge and GaP samples were implanted with 50 keV Xe⁺ ions to a dose around 10¹¹ ions/cm². At this implantation condition, each heavy ion created a small, spatially isolated amorphous zone. Following the ion implantation, the samples were irradiated with electrons having energies from 25 to 300 keV at temperatures 90 and 300 K. At each electron energy, transmission electron microscopy (TEM) images of a selected sample area were taken in regular time intervals to record the evolution of the implant damage. At all electron irradiation conditions it was observed that the amorphous zones shrunk with increasing electron dose and some of them eventually disappeared. The most interesting result is the observation that regrowth occurs below the displacement threshold and, moreover, regrowth rate increases when decreasing electron energy below ∼100, ∼125 and ∼200 keV, for Si, GaP and Ge, respectively. These results are discussed in terms of possible mechanisms stimulating regrowth.     

Tailoring electron vortex beams with customizable intensity patterns by electron diffraction holography

An electron vortex beam(EVB) carrying orbital angular momentum(OAM) plays a key role in a series of fundamental scientific researches, such as chiral energy-loss spectroscopy and magnetic dichroism spectroscopy. So far, almost all the experimentally created EVBs manifest isotropic doughnut intensity patterns. Here, based on the correlation between local divergence angle of electron beam and phase gradient along azimuthal direction, we show that free electrons can be tailored to EVBs with customi...