摘要:

Seeded, transient, stimulated Brillouin scattering (SBS) is studied using a new noniterative, numerical algorithm to solve this two‐point boundary value problem. The coupled pump, Stokes, and phonon equations are solved numerically, including the effects of pump depletion and a finite phonon lifetime. The noniterative approach leads to efficient computation (<30 s of cpu time, VAX 8000 series computer for 500 by 5000 points in space and time, respectively). The numerical study predicts transient oscillations in the pump and the Stokes intensities. The frequency of these oscillations depends on the phonon lifetime and the depleted, exponential SBS gain. This work is the first known prediction of these oscillations.

ISSN:0021-8979    

DOI:10.1063/1.350654

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, &lgr;, in the near‐field of the sample (<&lgr;/10). This technique, near‐field scanning optical microscopy, is sensitive to a variety of important sample properties including optical density, refractive index, luminescence, and birefringence. Although image contrast based on certain sample characteristics is similar to that observed in traditional optical microscopy, strong coupling between the probe and sample often produces contrast unique to the near‐field.

ISSN:0021-8979    

DOI:10.1063/1.350655

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Segmented optical waveguides in KTiOPO4are fabricated by ion exchange of Rb/Ba for K using molten nitrate salts. The waveguides have been utilized to generate efficient second‐harmonic generation (SHG) of blue light. Four techniques are described which demonstrate that the ion exchange can produce domain reversal in these waveguides, and quasi‐phase matching is utilized to obtain blue light. The experiments involve surface SHG, electrostatic toning, selective etching, and piezoelectric measurements.

ISSN:0021-8979    

DOI:10.1063/1.350656

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A neonlike x‐ray laser photoresonant pumping scheme is explored. An attractive design is a coaxial z‐pinch consisting of an inner krypton lasant plasma surrounded by a carbon shell that itself is surrounded by a stagnated krypton plasma. The photoresonant radiation emitted from the outer plasma passes inwardly through the carbon shell and photoexcites lasant electrons to the 3s, 3d, and 4dlevels. It is calculated that monochromatic pump powers of 30 GW/cm eV can be achieved for the 4dneonlike resonance line while powers of 100–200 GW/cm eV are attainable for the 3sand 3dresonance lines. The gain in several neonlike 3s‐3ptransitions is calculated as a function of temperature and density of the lasant plasma. Reasonable gain in only the 3p‐3s(J=0–1) transition is obtained for high‐density, high‐temperature lasant conditions. This gain, which is driven by monopole excitation from the ground state to the 3p(J=0) level, is nearly independent of the presence of pump radiation. For low‐density, low‐temperature lasants, optimal gain is obtained in the 3p‐3s(J=2–1) transitions. Under these conditions, the pump radiation is necessary to photoionize and photoexcite the lasant plasma to the neonlike stage while radiative decay from the resonantly pumped 4dlevel to the 3p(J=2) states provides the major upper lasing level pump mechanism.

ISSN:0021-8979    

DOI:10.1063/1.350657

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Calculations have been made for the electron acoustic signal in the case of one and two metallic layers deposited over a semiconductor substrate. The temperature repartition as a function of the depth has been determined by taking into account the absorbed power in the metallic layers and the substrate. We have considered strain‐free and constrained layers. Experimental results have been obtained for a single metallic layer (Au, W, Pd, Mo, Mn, Ti) deposited over GaAs and for Au‐Ti contacts. Comparison between experiments and calculations allows us to determine whether the layers are constrained or not.

ISSN:0021-8979    

DOI:10.1063/1.350658

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

It has recently been shown that the in‐plane acceleration sensitivity of contoured quartz resonators vanishes for a perfectly symmetric combined resonator plus support system. This indicates that a biconvex resonator will have lower resultant in‐plane acceleration sensitivity than a plano‐convex one because of its inherent additional symmetry. Since a plano‐convex resonator is easier to fabricate, an analysis of the degradation in the in‐plane acceleration sensitivity that arises from the contour being on one side only is performed. The calculations show that the in‐plane sensitivity of the plano‐convex resonator increases with decreasing radius of curvature and that the magnitude ranges over a few parts in 1012per g.

ISSN:0021-8979    

DOI:10.1063/1.350659

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The present paper is the first of a series reporting on a comprehensive study of the hydrodynamics, kinetics, and spectroscopy of the transient species formed following the detonation of lead azide (LA). The spatial and temporal behavior of the detonation products expanding into vacuum is obtained via high‐speed framing photography, transmission of a HeNe laser beam, and chemiluminescence from excited Pb atoms. The photography reveals that following the initiation of LA the products form an expanding, bell‐shaped cloud. The HeNe beam is attenuated when the cloud of products traverses its route. The attenuation starts 4–15 &mgr;s after initiation and depends on the height of the beam above the LA sample. The chemiluminescence consists of two components: the first, appearing 1–2 &mgr;s after initiation, is obtained from excited products formed by the detonation near the surface of the sample, while the second, starting 2–14 &mgr;s after initiation, originates from the expanding cloud of products.The intensity and the temporal behavior of the second component of chemiluminescence depend on the distance to a barrier placed above the LA sample. The cloud contains gaseous products and solid particles which propagate perpendicular to the LA surface with a maximum velocity of 4.48±0.10 km/s and 3.78±0.18 km/s, respectively. To reproduce the experimental results, two alternative hydrodynamic models are applied: Stanyukovich’s model [K. P. Stanyukovich,UnsteadyMotionofContinuousMedia(Pergamon, London, 1960), pp. 498–501] for isentropic expansion and London and Rosen’s model [R. A. London and M. D. Rosen, Phys. Fluids29, 3813 (1986)] for exploding foil. The latter model is preferred and when incorporating Beer’s law and Mie’s theory [C. F. Bohren and D. R. Huffman,AbsorptionandScatteringofLightinSmallParticles(Wiley, New York, 1983), p. 77] it reproduces very well both the temporal behavior of the second component of chemiluminescence and the attenuation of the HeNe beam and suggests that lead particles with radius of 0.05–0.15 &mgr;m are involved in the attenuation. The model also provides an estimate of the composition of the product cloud and of the density of the gaseous and solid species as a function of time and distance from the LA sample.

ISSN:0021-8979    

DOI:10.1063/1.350660

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The laboratory characterization of the interaction between a hollow cathode plasma source and an ambient plasma of ionospheric type is reported. The investigation was carried out by means of Langmuir probes for various positive polarization levels of the source with respect to the ambient plasma in absence of magnetic field. Measurements put into evidence the formation of a double layer that dominates the current collection process on the hollow cathode source. The electron energy distribution function, derived along the axis of the current path, indicates the presence of an anomalous collisional mechanism due to the bump‐in‐tail instability in the region between the double layer and the source. The experimental data were also compared with the results of a one‐dimensional theoretical model of the interaction; taking into account the approximation of the model, such a comparison indicates that both the position and the voltage drop associated to the double layer match rather well the theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.350661

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The detailed interaction of individual electrons with oscillating radio frequency (rf) sheaths is considered in this reexamination of the sheath heating process. We develop an analytic expression for the energy delivered to the discharge through sheath heating and that lost due to electron escape to the electrode. Using a simple model of the time‐dependent sheath electric field, we find that electron energy gain due to this process, averaged over an rf period is roughly proportional to the square of the maximum sheath speed and drops slightly with increasing electron temperature. Energy loss due to escaping electrons on the other hand, rises with temperature and ultimately outweighs gain when the average electron velocity exceeds the maximum sheath velocity. The requirement of a net power input to the plasma places upper bounds on bulk electron temperature and density attainable by plasmas to be maintained solely by this mechanism, independent of other aspects of container geometry. However, by increasing discharge frequency, power input can be increased for a fixed sheath voltage while reducing electron escape.

ISSN:0021-8979    

DOI:10.1063/1.350662

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A detailed kinetic study of silane‐germane glow discharges is presented. Stable gas decomposition and production rates have been measured using mass spectrometry and a kinetic model for the plasma chemistry is developed. It is found that germane depletes about four times faster than silane, nearly independently of their relative fractions. Germane is found to be much more reactive than silane with silylene, germalyn, and atomic hydrogen, and the silylene‐germane reaction leads in large part to film rather than stable gases. The spatial characteristics of the discharge are studied using optical emission and fiber deposition profiles. From these it is deduced that the present, low‐power discharge operates in a ‘‘hybrid’’ &agr;‐&ggr; regime, and that ion effects are important near the electrodes.

ISSN:0021-8979    

DOI:10.1063/1.350663

出版商:AIP    

年代:1992

数据来源: AIP