摘要:

Calculations of focus characteristics for x‐ray focusing systems using either flat or bent crystals with two‐dimensional modulated surfaces are presented. Based on the wave‐optics approach, the analytical formulas are derived for elliptical Fresnel zone structures (flat crystals) and linear Bragg zone structures (toroidally bent crystals). It is shown that for a given Si(111) reflection and Ti K&agr; radiation, a micron‐size focal spot can be achieved by using only one flat crystal with a modulated surface. The peak intensity is then nearly 100 times higher than that of the flat crystal without modulations. However, for a toroidally bent crystal with both Fresnel and Bragg diffraction amplitudes, the latter becomes dominant, since, due to the bending, the rapid oscillations of the Fresnel diffraction amplitude vanish. It is also shown that a focal spot of 0.3 &mgr;m for a bent crystal with linear Bragg zone structures is approximately four times narrower than that of an unmodulated surface. From the analysis, the modulated surfaces for cylindrically and spherically bent crystals are deduced to be a combination of Bragg and Fresnel zones. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360741

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

By use of the linear‐response dielectric theory and local electron density approximation, we calculate the energy straggling of protons in solids. The correlation and exchange interaction of electron gas in solids is taken into consideration by introducing a static local‐field‐correction function in the dielectric function. The theoretical results are compared with experimental and empirical data, as well as with other previous theoretical results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359767

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electromagnetic (EM) scattering in a medium containing discrete scatterers is a problem with broad interdisciplinary interest. The Mueller matrix solution has been applied to the study of EM polarimetric scattering and the vector radiative transfer from a layer of random medium. In this article, we report the methods to polarimetric scattering from a layer of particulate media containing: randomly dense spherical particles, nonuniformly oriented spheroids, or random clusters of spheroids. The complex scattering amplitude functions and phase matrix are explicitly obtained. Numerical results of the Mueller matrix solution show the properties of completely polarimetric scattering of those random media and its functional dependence on the relevant physical parameters. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359768

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The initial holographic recording rate has been analytically studied for a photorefractive thin slab. The finite thickness is explicitly taken into account by using a two‐dimensional formulation (coordinatesxandzparallel and perpendicular to the slab faces, respectively). It is shown that for a thickness comparable to the grating period, the solution appreciably departs from the usual one‐dimensional result, i.e., edge effects are remarkable. In particular, significant space‐charge fields perpendicular to the slab faces are generated. These effects may substantially modify the diffraction properties of the recorded photorefractive gratings, as exemplified for a GaAs film. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359769

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A nonintrusive three‐dimensional trap for microscopic particles in a liquid is described. The trap is based on acoustic radiation forces in an ultrasonic confocal standing‐wave cavity. Experiments at 11 MHz demonstrate the concept and verify the theoretically calculated forces. Theoretical calculations for higher‐frequency systems indicate a significant potential for low‐rms‐displacement trapping of submicrometer particles, making the trap suitable for nonintrusive scanning near‐field optical microscopy. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359770

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simplified discharge model for the prediction of the wave‐to‐plasma power transfer in high‐frequency collisional argon plasmas in the presence of a static magnetic field is presented. The study is based on the solutions to the homogeneous electron Boltzmann equation for an oscillating electric field composed of a right‐ and left‐hand‐side rotating parts, moving around the magnetic‐field lines. The mean absorbed power per electron to maintain the plasma is calculated for a container with nonconducting surfaces and the results are then compared with an experiment in the literature. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359771

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ion energy distribution functions (IEDF) were measured at the surface of a grounded or a rf‐powered electrode exposed to a microwave (MW, 2.45 GHz) or a rf (13.56 MHz) discharge in argon. The IEDFs measured on the grounded electrode in both the rf and the MW modes show a higher contribution of low‐energy ions when the pressure is raised. The maximum ion energyEmdecreased from 12.0 to 8.5 eV in the MW plasma, but remained at 26±0.5 eV in the rf plasma. The mean ion energyE¯ decreased from 6.1 to 3.8 eV (MW) and from 16.0 to 12.0 eV (rf) when the pressure was raised from 30 to 210 mTorr. The IEDFs in the rf mode exhibit a single peak, while a bimodal structure is observed in the MW mode. When the electrode is rf powered to achieve a negative dc bias voltageVB, theEmvalues reach ∼1.2eVB(rf) and ∼1.1eVB(MW), respectively. The IEDFs in the rf mode display a multiple peaked structure which is associated with a rf‐modulated sheath. In the dual‐frequency MW/rf mode the IEDF is single peaked, narrow, and centered aroundeVB. A nearly tenfold increase in the ion flux is observed when increasing the MW input power, while the ion energy remains unchanged for a constantVBvalue. This allows an independent control of ion energy and ion flux, suitable for the control of material properties in plasma processing. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359772

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The large electric fields in the cathode sheath of high pressure glow discharges lead to localized energy deposition in the gas, which drives a gas dynamic pressure wave into the region where the transient high pressure glow is homogeneous. For a range of parameters typical for discharge pumped XeCl‐lasers the gas density profiles of these waves have been measured interferometrically with high spatial resolution (20 &mgr;m). From comparisons with gas dynamic model calculations the amplitude and the spatial profile of the initial temperature distribution resulting from the energy deposition during the formation of the cathode sheath have been determined. These data can be used to verify assumptions to be made in future improvements of self consistent discharge models of the cathode sheath formation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359773

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The average electron density and electron density fluctuations in a dusty Ar/SiH4rf discharge have been studied using a microwave resonance technique. The average electron density increases with rf input power and it has a maximum as a function of pressure at about 30 mTorr. Within the first second of plasma operation the electron density decreases with a factor of ten. This is caused by submicroscopic particles, formed in the discharge, which rapidly absorb electrons. When the particles reach a critical size they are expelled from the plasma. This process is governed by a balance between the Coulomb force, trapping the particles in the positive plasma glow and the neutral drag force, flushing them out. The periodic growth and expulsion of particles, monitored by light scattering, results in an oscillatory behavior of the electron density. From the measured oscillation period (&tgr;), which is in the order of seconds to minutes, and its dependence on the gas flow rate (F) and on the fraction &agr; of SiH4in the plasma (&tgr;[s]≊4.5×102&agr;−1F−2[sccm], at 10 W rf power input), the trapping force (FC) on particles can be calculated:FC[N]≊4×10−18r[nm], whereris the radius of a particle. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359774

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The elastic interaction of an edge dislocation with a wedge crack is investigated using Muskhelishvili’s complex potential treatment of elasticity. The stress intensity factors induced by the dislocation, the strain energy, and the image force acting on the dislocation are formulated, calculated, and plotted. Especially, the influence of wedge angle on the shielding effects and on image forces is investigated. The results show that the radial component of the image force is inversely proportional to the distance from the crack tip to the dislocation and the tangential image force increases with increasing wedge angle as the dislocation position is kept unchanged. When the slip plane passes the crack tip, whether the edge dislocation shields or antishields the crack tip depends on its Burgers vector. In this case, the slip plane of the edge dislocation of Burgers vectorb1+ib2=bei&thgr;maxinclined at an angle &thgr;maxwith respect to the positive real axis corresponding to the maximum mode I crack shielding increases slightly to a maximum and then decreases with increasing wedge angle. Regardless of wedge angle, the maximum mode II shielding (or anti‐shielding) occurs when the dislocation is located at the positive real axis. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359775

出版商:AIP    

年代:1995

数据来源: AIP