摘要:

Neutral krypton atoms are excited from the ground state to the 4p56p[3/2]2state by two‐photon absorption from an ArF excimer laser operating at 193.41 nm. The third photon ionizes the krypton atoms. Excitation and ionization yields are theoretically computed employing the standard laser rate‐equations analysis. Measurements are made on both the excitation and ionization yields. The experimental results are in good agreement with the theoretical predictions of our formulations, as well as with those of other authors.

ISSN:0021-8979    

DOI:10.1063/1.341226

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The RADLAC‐II accelerator foilless diode injector was operated under double‐pulse conditions utilizing the RIIM accelerator as the test bed [M. G. Mazarakis, D. L. Smith, R. B. Miller, R. S. Clark, D. E. Hasti, D. L. Johnson, J. W. Poukey, K. R. Prestwich, and S. L. Shope, IEEE Trans. Nucl. Sci.NS‐32, 3237 (1985)]. The original RIIM accelerator pulsed‐power network was modified to provide for the generation, transmission, and delivery to the foilless diode of two distinct multimegavolt pulses with variable interpulse separation from 0 to 2 ms. The foilless diode successfully produced two 10‐kA current pulses with interpulse separations up to 1 &mgr;s. For larger separations, the generated plasma and an excessive neutral gas release following the first pulse prevented the diode from producing a second current pulse.

ISSN:0021-8979    

DOI:10.1063/1.341227

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An analysis of the parametric excitation of fast and slow space‐charge waves in a cylindrical metallic waveguide filled with relativistic beam electrons is presented. The pump wave in the laboratory reference frame consists of a static, spatially periodic axial electric field. Formulas are derived for the temporal growth rate and frequency of the backscattered fast space‐charge wave in both the laboratory and beam frames. The effects of a uniform axial magnetic field of arbitrary magnitude on the amplitude gain and frequency enhancement are studied.

ISSN:0021-8979    

DOI:10.1063/1.341228

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Diffraction of focused truncated Gaussian beams at a circular aperture is investigated experimentally. The beams are obtained from a uniformly illuminated Gaussian transmittance filter. The irradiance along the axis is measured point by point in order to demonstrate the existence of the focal shifts. Diffraction patterns in various planes normal to the axis are presented by photographs. Measured results are compared with theoretical predictions. Close agreement between them has been obtained.

ISSN:0021-8979    

DOI:10.1063/1.341229

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The perturbation method developed recently for analysis of planar phase change processes is extended to the case of time‐dependent temperature boundary conditions. Approximate solutions uniformly valid in time are derived. The role of time scales, that of the driving signal and the (time‐dependent) response time of the emerging phase, in the dynamics of a weakly nonlinear melting process is clarified. The short and long time asymptotics are studied in detail. The analytical results are compared with the numerical solution for the problem of melting in a semi‐infinite slab induced by a periodically varying boundary condition.

ISSN:0021-8979    

DOI:10.1063/1.341230

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The linear theory for the eigenfrequencies of the extended Pierce diode for resistive, capacitive, and inductive external circuits is tested via computer simulation with thepdw1 code, and is verified to within the accuracy of the simulation (between 1% and 0.01% depending on the circumstances). The simulations were remarkably inexpensive in terms of computer time, and could have been performed on a personal computer.

ISSN:0021-8979    

DOI:10.1063/1.341231

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The dislocation densities, surface morphology, and strain of Ga1−xInxAs/GaAs epitaxial interfaces as a function of indium composition and layer thickness have been investigated by transmission electron microscopy, medium energy ion blocking, and double‐crystal x‐ray diffractometry. The electron microscopy shows that in the thinnest dislocated films (90 and 160 nm,x=0.07) 60° &agr; dislocations form first in one ⟨110⟩ direction at the interface. Surprisingly, however, an asymmetry in residual layer strain is not detected in these samples, suggesting that the dislocations have the same Burgers vector or are evenly distributed between two Burgers vectors. Orthogonal arrays of dislocations are observed in films thicker than 300 nm (60° and edge‐type,x=0.07). In this case, dislocation densities in each ⟨110⟩ direction are equal to within experimental error while an asymmetry in in‐plane strain is measured (18% and 30% forx=0.07, 300, and 580 nm thick, respectively). An unequal distribution of Burgers vectors of 60° or edge‐type dislocations is considered responsible for the strain asymmetry in these thicker samples.

ISSN:0021-8979    

DOI:10.1063/1.341232

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The kinetics of reversible resistivity changes during structural relaxation in various Co‐Fe based metallic glasses was examined using a nonlinear kinetic form &PSgr;=exp[−(t/&tgr;m)n]. It was found that the data excellently fit the nonlinear kinetic form. The compositional dependence of the kinetic parameters (distribution parametern, activation energyEa, and preexponential factor &tgr;0) were obtained, and the microscopic mechanism of atomic rearrangements during the relaxation is discussed.

ISSN:0021-8979    

DOI:10.1063/1.341233

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new theoretical framework has been developed which is applicable to the implantation and ion‐induced release of hydrogen isotopes in graphite. It provides a physical basis and a refinement of the predictions of the simple model of local saturation and mixing. The model treats the trapping at defects and a local release of trapped atoms by nuclear knock‐on. Ion deposition and damage functions are taken fromtrimsimulations. The detrapped atoms may become retrapped or recombine to molecules, which then are transported to the surface by fast molecular diffusion, and subsequently released. By the choice of suitable rate constants in the model calculations, different experimental findings for the implantation and high‐fluence self‐reemission of deuterons in graphite may be explained consistently. Examples cover the saturation as a function of temperature and energy, depth profiles, gas reemission, thermal desorption, and effects of predamage.

ISSN:0021-8979    

DOI:10.1063/1.341234

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Analytic expressions are obtained using the generalized geometrical‐optics approximation for the field‐off state optical field and transmission of the general double layer twisted nematic and supertwisted nematic liquid crystal displays with arbitrary display parameters. A variety of display characteristics can be obtained from such structures. In particular, the strong interference colors in the field‐off state single layer supertwisted nematic displays can be completely removed in a double layer supertwisted nematic display; thus, a black or white off state is possible. For the double layer 90° twisted nematic, besides the complete black or white field‐off state, it can also exhibit off state display performance similar to that for either the single layer 180° supertwisted nematic or the optical mode interference display.

ISSN:0021-8979    

DOI:10.1063/1.341235

出版商:AIP    

年代:1988

数据来源: AIP