摘要:

Calculations are described and results are given for the focusing properties of six curved x‐ray diffractors for Bragg angles ranging from 15° to 75°. The geometries considered include cylindrical, spherical, and toroidal cases. The type of slit necessary to eliminate stray radiation in applications of doubly curved diffractors to scanning monochromators is discussed. Three of the most efficient diffractors are compared with respect to the solid angle for collection of x rays and the possible spectral resolution. A diffractor with spherically curved planes and toroidally curved surface is shown to be superior to the Johansson geometry and the spherically curved plate.

ISSN:0021-8979    

DOI:10.1063/1.346834

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effective longitudinal dielectric constant is calculated for an infinite, three‐dimensional, rectangular lattice of identical, parallel, conducting prolate spheroids. The problem is formulated by means of a matrix equation. The matrix elements are explicitly worked out. The matrix equation embodies all the multipole interactions among the spheroids exactly, and is solved analytically by iteration. An exact solution is obtained formally as an infinite series. It is shown that the interaction effects can be quantified completely by a shift in value of the depolarization factor of the spheroids. In the spherical limit, the results reduce properly to those previously derived directly for a lattice of spheres. In the opposite, acicular limit, the interaction‐shifted depolarization factor is obtained in closed form, and numerical results are presented. The calculation of the effective longitudinal magnetic permeability of a lattice of magnetic prolate spheroids is similar. The magnetic permeability is obtainable from the dielectric constant by simple variable substitutions.

ISSN:0021-8979    

DOI:10.1063/1.346835

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Measurements of the effective electric dipole moments of conducting particle chains suspended in insulating dielectric liquid reveal the influence of dielectric breakdown between particles. This breakdown can lead to reversal of the sign of the interparticle force from attractive to repulsive. Other measurements with a vibrating sample magnetometer of the effective magnetic dipole moments of ferromagnetic particle chains provide clear evidence that chaining enhances nonlinear magnetization at a field intensity about a factor of 10 below the value at which saturation is observed for single particles. Both of these physical situations are examples of how nonlinear effects can influence the electromechanical interactions of closely spaced particles. The nonlinearity is caused by the very strong field intensification that occurs in the gaps between particles for chains parallel to an applied electric or magnetic field. A correspondingly strong nonlinear effect is predicted for the forces between particles in chains.

ISSN:0021-8979    

DOI:10.1063/1.346836

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper reports theoretical and experimental work on the transport of space‐charge‐dominated relativistic electron beams in a racetrack betatron with cusp focusing. High‐efficiency propagation of 550‐keV, 280‐A beams through a complex optical system consisting of two 180° arcs with 36 focusing cells and a straight section was observed. More than 90% of the injected beam was captured and transported through the 7‐m system. The experiments resolved several recent problems of beam injection and trapping in the machine and showed that electron beam transport at the space‐charge limit is possible in a curved cusp array despite strong axial variations of focusing forces. We encountered no problems with the transitions between curved and straight focusing sections. The experiments demonstrated good beam containment in a cusp array with mixed focusing cell geometries as long as the axially averaged focusing force was the same for all cells. The ability to use long cells is a critical feasibility issue for other planned injection experiments into a closed racetrack geometry.

ISSN:0021-8979    

DOI:10.1063/1.346837

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The quasistatic magnetic field penetration through a circular aperture of a spherical shield enclosing a spherical conductor is considered in the framework of the dual series equations theory. Both cases of an applied magnetic field parallel and perpendicular to the system’s symmetry axis are analyzed. Induced currents on the cavity and internal sphere surfaces are calculated, as well as the aperture effective dipole moment and polarizability. Convergence of the different series involved is discussed. The magnetic field behavior at the aperture edge is also investigated, and the discontinuity occurring in this region is treated analytically. The theoretical analysis is finally complemented and illustrated by several numerical results.

ISSN:0021-8979    

DOI:10.1063/1.346838

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Different resonant distributions of current in circular arrays withN=60, 72, and 90 elements are investigated theoretically with the method of symmetrical components and a two‐term representation of current in each element. The arrays studied have only one driven element. The remarkable results—which are displayed in a sequence of graphs—indicate that the relative currents in the elements can be distributed in triplets, triplets alternating with singlets, two independent sets of singlets, or one set of singlets. The driving‐point impedance of this last distribution is a pure resistance, theQof the 90‐element array is over 30 000, and the half‐power beamwidth of each of the 90 sharp peaks in the power pattern is 2°.

ISSN:0021-8979    

DOI:10.1063/1.346839

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

By monitoring photoluminescence (PL) in real time andinsitu, hydrogen plasma operating conditions have been optimized for surface passivation of native‐oxide‐contaminated GaAs. PL enhancement is critically dependent on exposure time and pressure because of competition between plasma passivation and damage. Optimal exposure time and pressure are inversely related; thus, previous reports of ineffective passivation at room temperature result from overexposure at low pressure. Plasma treatment is effective in removing As to leave a Ga‐rich oxide; removal of excess As increases the photoluminescence yield as the corresponding near‐midgap‐state density is reduced. Passivation is stable for more than a month. These results demonstrate the power of real time monitoring for optimizing plasma processing of optoelectronic materials.

ISSN:0021-8979    

DOI:10.1063/1.346813

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The scattering of a transverse electric plane wave incident from a linear media by a nonlinear Kerr film deposited on a good conductor is studied. Self‐focusing and self‐defocusing are included both above and below the critical angle. The solution to the complex second‐order nonlinear differential wave equation is constrained at the nonlinear/conductor planar interface by mixed boundary conditions and at the linear/nonlinear interface by the continuity of the tangential electric and magnetic fields. A potential‐well approach is employed to classify and isolate the various solutions. Several examples illustrate the two nonlinear analogies of the evanescent and harmonic field solutions. Additionally, we obtain the surface‐wave solutions and the transitional, hybrid, fields. Finally, we show that the reflectivity is multistable with respect to the incident intensity and that the reflected intensity is multistable as the incident angle changes for a constant input intensity.

ISSN:0021-8979    

DOI:10.1063/1.346814

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The second harmonic generation (SHG) coefficientsdijof several corona‐poled guest‐host and side‐chain polymers have been measured and studied over time using a new Maker Fringe analysis. The electro‐optic coefficientr33and scattering losses have also been measured in thin‐film waveguides, on silicon and glass substrates, made from some of the polymers. Kleinman symmetry (d15=d31) was not valid for near‐resonant SHG in these materials andd15/d31was determined. Stable values ofd33, for a fundamental of 1.064 &mgr;m, were as high as 40 pm/V for one of the side‐chain polymers. Optical waveguide losses determined from scattering measurements were as low as 0.4 dB/cm at 1.06 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.346815

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The purpose of this article is to establish the focusing properties of a new kind of transducer consisting of circular electrodes deposited on an isotropic substrate and covered by a thin piezoelectric layer. We first express the electromechanical equations of the device and determine its boundary conditions. Then, using the effective dielectric function and an appropriate approximation of the charge density, we obtain various functions (electric potential, displacements) giving a physical description of each medium. Last, we present the numerical results of our study, namely those concerning the displacements and proving the focusing capabilities of our device.

ISSN:0021-8979    

DOI:10.1063/1.346816

出版商:AIP    

年代:1990

数据来源: AIP