摘要:

The spatial structure and coherence properties of 10.6‐&mgr;m light scattered from CO2laser‐target interactions in oblique incidence show many unexpected features. It is found that the Brillouin backscatter is neither a phase conjugate nor a ray retrace of the incident beam. Rather, it shows a preference for scattering directions other than those exactly antiparallel to the incident beam, apparently related to the angular distribution of the scattering source and also of the plasma corona that serves as the Brillouin amplifying medium. As well, the backscatter phasefront is strongly perturbed with respect to the incident phasefront. This is an indication of turbulence in the corona and/or memory of the structure in the source that is then amplified. Small‐scale structures seen in the reimaged backscatter are due to phase perturbation and cannot be simply interpreted as geometric images of a (filamented) source. The phasefront of light that is scattered obliquely from the plasma is much more coherent.

ISSN:0021-8979    

DOI:10.1063/1.331170

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Brillouin backscattering instability is studied for a range of preformed plasma conditions and using a CO2laser in the 1012–1013W/cm2regime. A short prepulse is incident on a planar target ahead of the main‐pulse to produce the preformed plasma. The instability appears in a short burst of back‐reflected light. Saturation of the backscatter level is observed for an individual increase of the prepulse energy, main‐pulse intensity, and prepulse‐to‐main‐pulse delay. Ion Landau damping is strong and average back‐reflected intensities are limited to less than 30% of incident. Backscattered light spectra suggest that the critical surface is involved in the backscatter process when the laser beam is at best focus onto the target surface. Otherwise, the spectral signature is similar to those obtained from underdense plasmas.

ISSN:0021-8979    

DOI:10.1063/1.331171

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Small amounts of dye vapors are mixed with helium in a positive column of a direct‐current discharge. The distributions of dye vapor from a central reservoir towards the anode and towards the cathode are asymmetrical due to cataphoresis. In addition to this, the concentration of dye vapor along the tube axis sharply decreases with distance form the reservoir due to dissociation by electronic collision. From the comparison between experimental and calculated results the degree of ionization &agr; is estimated to be 10−3∼10−4for 1,4‐Di‐[2‐(5‐phenyloxazolyl)]‐benzene (POPOP) and 3×10−3for perylene, and the cross section for dissociation by electronic collision &sgr;dis estimated to be 2×10−16cm2for both POPOP and perylene. The upper limit of pulse rise time, required to produce a dye vapor discharge with positive gain, is discussed in relation to the value of &sgr;d.

ISSN:0021-8979    

DOI:10.1063/1.331172

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Fireball generation from a high‐intensity circuit breaker arc is interpreted here as a quantum‐mechanical phenomenon caused by severe cooling of electrode material evaporating from contact surfaces. According to the proposed mechanism, quantum effects appear in the arc plasma when the radius of one magnetic flux quantum inside solid electrode material has shrunk to one London penetration length. A formula derived for the threshold discharge current preceding fireball generation is found compatible with data reported by Silberg. This formula predicts linear scaling of the threshold current with the circuit breaker’s electrode radius and concentration of conduction electrons.

ISSN:0021-8979    

DOI:10.1063/1.331173

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Transmission electron microscopy is used to characterize the hole‐formation process due to laser writing in evaporated and sputtered Te thin films and in a Se‐Te bilayer. Bilayers, with Se as the top layer, combine the effect of an antireflective coating with protection against oxidation and provide the advantage of alloy formation during spot writing. Solidification of the melt in the Se‐Te spot takes place as an amorphous alloy resulting in smooth‐rimmed, clean holes. In contrast, Te crystallizes from the melt, giving rise to uneven rims and debris inside the spot.

ISSN:0021-8979    

DOI:10.1063/1.331174

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Amorphous Fe40Ni40P12B6was compressed in the diamond anvil cell up to a 250 kbar pressure, and the pressure was measured as a function of position with the ruby fluorescence method. Analysis of the spatial distribution of the pressure indicates that the flow stress &sgr;yof the material varies as &sgr;y= 17 exp(0.004P), with &sgr;yandPexpressed in units of kbar. The increase in the flow stress with pressure corresponds to an activation volume of 0.16 A˚.3The pre‐exponential factor represents the flow stress of the material at zero pressure. Because the material in a diamond cell is subjected to a very extensive plastic flow before the pressure distribution is established, this value is not necessarily identical to the flow stress measured with more conventional methods, involving no or very little prior plastic deformation. The latter methods tend to measure higher values for &sgr;y, indicating that metallic glasses undergo work softening when deformed extensively.

ISSN:0021-8979    

DOI:10.1063/1.331175

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

It is shown that the sequential implantation of 20–200 keV C+and N+ions into a KCl crystal gives rise to formation of the CN−molecular configuration. Detection of the CN−is by the characteristic luminescence spectrum induced when He+ions are incident on the implanted target, a technique which represents a directinsitudetermination of their presence. It is shown how the ion‐induced optical emission may be used to provide a routine relative measurement of the quantity of CN−present. We describe a phenomenological model of the formation process which leads to the conclusion that each incoming ion searches a volume of the target approximately 3.4×10−21cm3in extent and has a unit probability of combining with an atom of the other species lying in this region. This model explains why saturation of the CN−density occurs at a N+dose independent of the quantity of C+implanted previously.

ISSN:0021-8979    

DOI:10.1063/1.331176

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Trapping of ion‐implanted deuterium by lattice defects in nickel has been studied by ion‐beam‐analysis techniques in the temperature range between 30 and 380 K. The deuterium‐depth profiles were determined by measuring either the &agr; particles or the protons from the3He‐excited nuclear reactionD(3He,&agr;)p, and the deuterium lattice location was obtained by means of ion channeling. Linear‐ramp annealing (1 K/min) following a 10‐keVD+implantation in nickel produced two annealing stages at 275 and 320 K, respectively. The release‐vs‐temperature data were analyzed by solving the diffusion equation with appropriate trapping terms, yielding 0.24 and 0.43 eV for the trap‐binding enthalpies associated with the two stages, referred to as an untrapped solution site. The 0.24‐eV trap corresponds to deuterium close to the octahedral interstitial site where it is believed to be trapped at a vacancy, whereas it is suggested that the defect correlated with the 0.43‐eV trap is a multiple‐vacancy defect. The previously air‐exposed and electropolished nickel surface was essentially permeable; the surface‐recombination coefficient was determined to beK≳10−19cm4/s at 350 K.

ISSN:0021-8979    

DOI:10.1063/1.331132

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

By means of ion‐beam‐analysis techniques, the trapping of deuterium implanted into nickel preimplanted with helium was investigated in the temperature range 100–500 K. Following room‐temperature helium implantations and deuterium implantations at ∼100 K, linear‐ramp annealing (1–2 K/min) was carried out, while the deuterium concentration within the near‐surface region (0–0.5 &mgr;m) was monitored by use of the nuclear reaction D(3He,&agr;)1H. The release curves were analyzed by solving a diffusion equation with the appropriate trapping terms. In addition to trapping by lattice defects, stronger helium‐associated traps were found with a binding enthalpy of 0.55±0.05 eV relative to a solution site. We propose that the responsible entities are small helium bubbles observed in the implanted material by transmission electron microscopy.

ISSN:0021-8979    

DOI:10.1063/1.331133

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A new method is described for determining the primary elastic constants (stiffnessescij’s and compliancessij’s) with respect to the crystallographic axes. Although we will consider only cubic materials the method can be applied to materials of lower symmetry. The method utilizes the symmetry present in a textured (preferred growth) foil and can be used for cases when bulk single crystals are difficult to prepare for ultrasonic experiments. The method involves the use of expressions, that have not been previously derived, relating the biaxial, flexural, Young’s and shear modulus to the primary elastic constants for textured foils. The agreement of the experimentally observed moduli with ones calculated from the expressions to be presented demonstrates that the accuracy is comparable with existing methods.

ISSN:0021-8979    

DOI:10.1063/1.331134

出版商:AIP    

年代:1982

数据来源: AIP