Shape-invariance error for axially symmetric light beams

A significant aspect of the propagation of coherent light beams is that the shape of the transverse field distribution changes. In this paper, the concepts of shape-invariance error and shape-invariance range are used to characterize such effects in a quantitative way. Applications of the theoretical analysis to some simple but significant cases are presented     

An offset-fed reflector antenna with an axially symmetric main reflector

A design method for an offset-fed, dual reflector antenna (Cassegrain type or Gregorian type) system with an axisymmetric main reflector is presented. Geometrical optics (GO) and the geometrical theory of diffraction (GTD) are used to find the surface-current density on the main reflector. A modified Jacobi-Bessel series (JBS) method is used to find the far-field pattern for the physical optics (PO) integral. In the defocused mode of operation, a new technique is developed to find the reflection point on the subreflector corresponding to the defocused feed and a general field point on the main reflector. Two sample systems are designed.     

非轴对称腔板条固体激光器

本文使用复曲率张量Q-1自再现法分析了柱面-球面镜非轴对称腔的特性,并用数值计算例说明。报导和讨论了我们的非轴对称腔板条固体激光器的实验结果。     

掺铈铌酸锂相位共轭腔的双稳输出特性

以掺铈铌酸单晶为相位共轭镜构成了相位共轭光腔,测量了它的稳态输入输出特性。该特性表现出明显的双稳态。     

Generalized classical axially symmetric dual-reflector antennas

This work presents a generalized study of classical axially symmetric dual-reflector antennas. The antenna dishes are simply described by conic sections, arranged to reduce the main-reflector radiation toward the subreflector surface. The dual-reflector configuration provides a uniform-phase field distribution over the illuminated portion of the aperture, starting from a spherical-wave feed source at the antenna primary focus. All possible configurations are characterized into a total of four distinct groups. Simple closed-form design equations and the aperture field distribution are derived, in a unified way, for all these kinds of generalized antennas using the principles of geometrical optics. The formulation is applied in a parametric study to establish the configurations yielding maximum radiation efficiency (not including diffraction effects). The design procedure is exemplified in the synthesis of a novel configuration, which is further analyzed by the moment method     

带SBS池的位相共轭激光器调Q机理的研究

本文从速率方程出发,分析了带SBS池的Nd∶YAG位相共轭激光器的调Q机理,给出了调Q的理论模型。用数值计算方法求出了输出调Q脉冲的腔内光子数密度与时间的关系曲线,与实验值基本相符。     

Crosspolarisation characteristics of axially symmetric reflectors

The crosspolarisation levels of symmetric front-fed paraboloids and dual-reflector antenna systems have been determined for a wide range of reflector and feed parameters. It is shown that minimum crosspolarisation is achieved when the feed radiates a polarisation-pure field, and, in this case, the front-fed paraboloid is superior.     

The geometrical theory of diffraction for axially symmetric reflectors

The geometrical theory of diffraction (GTD) (cf. [1], for example) may be applied advantageously to many axially symmetric reflector antenna geometries. The material in this communication presents analytical, computational, and experimental results for commonly encountered reflector geometries, both to illustrate the general principles and to present a compact summary of generally applicable formulas.     

Iterative integral equation solution for cylindrical dielectric resonator

An exact integral equation describing the substrate-mounted open cylindrical dielectric resonator is derived, and a first approximate solution for the fundamental resonant mode is calculated. Results are presented and are compared with both experiment and another theoretical approach.     

Transient response of thick axially symmetric monopoles

The steady-state results for thick hemispherically capped monopoles with or without conical feed sections are used to construct the transient response of such monopoles. For a voltage pulse excitation, file transient waveforms for the transmitted-reflected feed currents, the radiated fields in different directions, and the instantaneous currents on the monopoles are calculated and presented. Steady-state results are obtained by solving the scalar potential integral equation with the axis extended boundary condition using the moment method.     

Forward radiation from axially symmetric reflector antennas

The fields radiated from focus-fed symmetric reflector antennas in the vicinity of forward axial direction are determined by a series representation of the physical optics integral. The considered feeds have cosine-tapered patterns with different tapers inE- andH-planes. The influence of feed pattern asymmetry, subreflector blockage, feed taper, focal distance to diameter (f/D) ratio and the reflector size on the performance parameters of paraboloidal, Cassegrain, near-field Cassegrain, and corresponding Gregorian antennas is investigated. Design curves are presented to predict the performance parameters of the considered antennas.     

An asymptotic-series solution for the vicinity of emitting surfaces of an axially symmetric bipolar beam

For the vicinities of arbitrary axially symmetric emitting surfaces, solutions to the beam equation are obtained in the case of counter motion of nonrelativistic nonmagnetized ions and relativistic electrons in an external magnetic field. The boundary value problem of determining the emission current in the ρ mode and the electric field on the cathode in the T mode or the problem of determining the shape of the plasma boundary in the r mode, which is related to the enhancement of the accuracy of trajectory analysis programs, is considered.     

Small efficient axially symmetric dual reflector antennas

Two efficient small dual reflector antenna designs are analyzed using the method of moments. One is based on the standard Cassegrain system and the other is a displaced axis design. Both incorporate a low-blockage feed consisting of a dipole radiating in the presence of parasitic elements. In the first case, efficiencies greater than 55% were obtained for 20-wavelength main reflectors; in the second, an efficiency greater than 67% was achieved for a 22-wavelength main reflector     

小Fresnel数轴对称光腔场分布计算

本文给出了计算一般球面反射镜轴对称激光谐振腔场分布的方法.利用此方法,计算了小Fresnel数的光腔腔内的场分布及输出光束的强度分布.计算所得结果与实验观察到的现象相同.     

相位共轭光腔研究进展

相位共轭光腔能消除腔内的波前畸变和介质扰动，从而能提高输出激光束的性能和质量，本文对近年来这一领域的理论和实验研究作了概述。     

Magnetic compression of axially symmetric Brillouin-focused electron beams

A study has been made of high-current density Brillouin-focused electron beams formed with magnetic compression. Analysis of the problem was by numerical calculation of electron trajectories using a digital computer. Electrostatic field data were measured using a resistance network analog. The effect of the magnetic field was calculated as an equivalent potential. An experimental system based on the results of the analysis was designed and tested. A Müller-type electron gun was found to provide a more uniform current density than a corresponding Pierce type. Experimental results were in close agreement with design objectives. For an area magnetic compression of 10 to 1, a focused beam approaching ideal Brillouin flow was achieved.     

Digital computer analysis of axially symmetric electron guns

A digital computer program written in the IBM 7090 FORTRAN programming system is described and then employed in the analysis of several axially symmetric electron guns. The digital program employs relaxation techniques while alternately computing electric fields and trajectories. One cycle through the program consists of three parts. 1) Calculation of the voltages within the electron gun by solving Poisson's equation, in difference form, on a matrix containing a maximum of 10 000 points on which electrode potentials are laid out. 2) Calculations of new current densities along the cathode and the setting up of new trajectory starting points along the cathode to simulate these current densities. 3) Calculations of trajectories, including magnetic fields and relativistic effects if desired, and comparison of the new beam with the previous one. Thermal effects and direct particle-particle interaction effects are ignored although space-charge effects, introduced through the field calculations, tend to prevent excessive or usual trajectory crossings. Execution time for the entire program is between 4 and 12 minutes, although for most guns 5 to 7 minutes is usually sufficient. Results produced by the program are presented and compared with experimental and analytical results.     

Adaptive beamforming with conjugate symmetric weights

The Hermitian persymmetric maximum likelihood estimator (MLE) is better than the conventional MLE in estimating the covariance matrix of a symmetrically distributed antenna array. Though using the Hermitian persymmetric MLE improves the performance of adaptive beamforming, it increases the computational load due to the forward-backward averaging of array input sample data. By observing that the weight vector obtained from the Hermitian persymmetric MLE is conjugate symmetric if the phase origin is chosen at the array geometry center, methods are developed to reduce the computational load of the direct-form beamformer and the generalized sidelobe canceler (GSC). The weights of both beamformers can be adapted with real computations, with significant savings in computation time     

Calculation of optimum spacing for a three coil axially symmetric metal detector

When designing an in-line metal detector, a three coil axially symmetric design is often employed. For maximum sensitivity to small particles, the spacing of the coils is an important factor. A formula is derived which predicts the signal produced by a metal sphere when moved along the axis of such a detector and from this a graph is produced to determine the optimum coil spacing.<>