摘要:

This paper deals semiquantitatively with the phenomenon of quasiresonant laser‐produced plasma (QRLPP) generation, i.e., breakdown of an atomic vapor when a laser beam couples a resonant excited state with a high excited state. The origin of the breakdown, threshold conditions for the breakdown, and the the effect of inducible absorption are discussed. Furthermore, the QRLPP may exhibit an unusual asymmetrical behavior (observed for a Cs plasma) when the single mode cw dye laser is tuned near the quasiresonant absorption line: on the low‐frequency wing, ’’noise‐reduction’’ effect for the transmitted beam is observed, while on the high‐frequency wing, ’’self‐oscillation’’ of the plasma is observed. The self‐oscillation seems to result from a periodic plasma diffusion from the laser focus. The QRLPP, produced by cw or pulsed lasers, is a very efficient plasma generation mechanism which appears to be useful for many atomic vapors, and the potential applications are discussed.

ISSN:0021-8979    

DOI:10.1063/1.328341

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A collisional Monte Carlo electron transport model has been combined with an existing relativistic electron beam diode simulation code to investigate the effect of electron material interactions on diode performance. The effects of electron scattering and deposition in various anode materials on the electron beam profile are detailed. Simulations of two enhanced electron deposition experiments are described.

ISSN:0021-8979    

DOI:10.1063/1.328342

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A fast, high‐densityz‐pinch discharge is suitable for the study of CO2laser‐plasma interactions. The plasma was investigated temporally and spatially using a variety of optical diagnostic techniques including streak and shadowgram photography, spectroscopy, and Thomson scattering off ion acoustic fluctuations. Peak electron densities of 4×1019cm−3and ion temperatures of 50 eV are observed. Shadowgrams show that at peak compression the plasma consists of an inner dense corene≳1019cm−31 mm in diameter surrounded by a low‐density regionne∼1018cm−3that extends to a diameter of 4 mm.

ISSN:0021-8979    

DOI:10.1063/1.328343

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The assumptions of straightforward moment models advanced to describe the equilibrium positive column in O2discharges are examined in a derivation from first principles. A particular such model employed by others is shown to lead, with the addition of consistent models for ionization, recombination, and mobility, to a nonlinear two‐point characteristic value problem. This problem is shown to have two distinct physically acceptable solutions at certain O2pressures. In one of these solutions, ratios of the number densities of the charged species are constants across the column, while the ratios vary with radial position in the other.

ISSN:0021-8979    

DOI:10.1063/1.328344

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

One of the consequences of anode spot formation in high‐current vacuum arcs is the ejection of molten metal droplets of varying sizes and the impact cooling of these droplets upon the internal surfaces which surround the discharge. Some of these droplets adhere to the target surfaces while others becomes detached to form loose metallic debris within the containing vessel. Under some conditions, high voltage applied to the vessel can levitate the debris causing electrical breakdown. We have simulated this breakdown mechanism in an experimental study of particles having cylindrical shapes moving under the influence of high‐voltage pulses of several milliseconds duration. The motion of aluminum, copper, and gold particles is determined using a stroboscopic technique. Values of levitation voltages under dc conditions are also measured and found to be in good agreement with an analysis by Felici. We have conducted a numerical analysis of the dynamic behavior of the particles studied in the experiment. The results, which take into account the image forces and the instantaneous state of contact of the particle with the supporting surface, correlate well with the experiment. A brief extension of the analysis is made to describe particle movement under impulsive, sinusoidal, and 1‐cosine voltage waveforms. Significant motion of particles 2 mm in length and 0.25 mm in diameter occurs within a few milliseconds.

ISSN:0021-8979    

DOI:10.1063/1.328345

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We have measured the effects of pressure, temperature, and some variations in impurity content on the growth rateuof quartz into fused silica. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging −21.2 cm3/mole. The activation enthalpy for all specimens extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear termCOHin the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Alsouis increased as the ideal stoichiometry is approached from the partially reduced state.

ISSN:0021-8979    

DOI:10.1063/1.328346

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The distributions of Bi ions implanted into the double‐layer structures Si/Ge, Ge/Si, C/Si, and C/Ge have been determined using MeV He backscattering techniques. A discontinuity of the backscattering yield was found in the Bi spectrum at or near the energy corresponding to the interface between film and substrate. In each case the magnitude of the interface discontinuity in the ion concentration, which was derived from this backscattering yield, coincided with the theoretical predictions within the experimental error of 20%.

ISSN:0021-8979    

DOI:10.1063/1.328347

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The dependence of the carrier concentration on the implantation dose and on the temperature was investigated in ion‐implanted thin films of Pb1−xSnxTe (0⩽x<0.1). By assuming a twofold defect level in the conduction band we are able to fit the experimental results. With increasing tin content the energy of the defect level shifts towards the conduction‐band edge. By extending the results to SnTe a general model for the understanding of the electrical properties of ion‐implanted Pb1−xSnxTe (0⩽x⩽1) is suggested.

ISSN:0021-8979    

DOI:10.1063/1.328283

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Oxygen implantation in ZnTe may be used to obtain optical absorption at wavelengths higher than 0.55 &mgr;m, which is the normal absorption edge in this compound semiconductor. Optical waveguides obtained by boron implantation in this material are associated with detectors using that extrinsic absorption effect in the presence of a Schottky barrier depletion layer. The responsivity of the photodetector is about 5×10−2A/W at 0.61 &mgr;m and the rise time is less than 3 ns.

ISSN:0021-8979    

DOI:10.1063/1.328303

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The electrical properties of Mg‐implanted GaAs have been studied in detail using the van der Pauw technique. Mg ions were implanted in Cr‐doped semi‐insulating GaAs at 120 keV to doses of 1×1013–3×1015/cm2at room temperature. The implanted samples were annealed with rf‐plasma‐deposited Si3N4encapsulants at temperatures ranging from 600 to 850 °C.p‐type layers have been produced for all dose levels. The maximum electrical activation occurred at an annealing temperature of 750 °C for all except the lowest dose of 1×1013/cm2. An electrical‐activation efficiency as high as 85% was obtained for the sample implanted to a dose of 3×1013/cm2and annealed at 750 °C. The dopant profiles were very sensitive to annealing temperature and ion dose, broadening significantly at or above 750 °C. Double peaks in the depth profiles have been observed for doses of ?1×1014/cm2, and the maximum carrier concentration obtained was as high as 2×1019/cm3.

ISSN:0021-8979    

DOI:10.1063/1.328304

出版商:AIP    

年代:1980

数据来源: AIP