摘要:

Maxwell’s equations, which govern the magnetic, current density, and electric field vector distributions throughout a plasma have been formulated and solved in an inverse manner. The methodology allows the geometrical configuration of those components which bound the plasma to be determined in physical space, given the magnitude of the relevant field vectors on their surfaces (boundaries of the computation region in a transformed plane). To accommodate the required mathematical structure of the analysis, a uniform plasma flow at low magnetic Reynolds number is considered in which ion slip and electron pressure/temperature gradient diffusion effects are negligible.

ISSN:0021-8979    

DOI:10.1063/1.328594

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

One of the major motivations for using computerized waveform capture for deep‐level transient spectroscopy is the capability to employ methods of analysis more accurate and informative than boxcars and correlators. Accordingly, we have adapted the fast Fourier transform method and the method of moments to analyze single and multiple exponential decays, respectively. We present relevant details of our experimental system, and compare the boxcar method with the new analyses on both simulated and experimental data. The new analyses have given conclusive, accurate results in cases where the boxcar is ambiguous or directly misleading.

ISSN:0021-8979    

DOI:10.1063/1.328595

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Under the joint action of homogeneous magnetic fields and ambient media, relativistic charged particles emit synchrotron‐Cˇerenkov radiation. The behavior of this radiation in the vicinity of an atomic absorption edge is studied in detail. Theoretical estimates indicate that synchrotron‐Cˇerenkov radiation can be exploited for the measurement of dispersive interactions in the x‐ray region of the spectrum in parameter ranges not accessible by other techniques. TheKedge of krypton appears to be a conceptually clean‐cut case which is particularly suited for experimental tests; detailed predictions for the intensity of synchrotron‐Cˇerenkov radiation in the vicinity of thisKedge are given. With 20‐GeV electrons and fields of the order of a few kilogauss, it should be possible to measure deviations from unity of the index of refraction to a precision of 1 part in 109at photon energies of 14.3 keV.

ISSN:0021-8979    

DOI:10.1063/1.328596

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A simple analytic central potential with two adjustable parameters is proposed for the helium isoelectronic sequence. The potential parameters are obtained by appealing to the precise values of optical oscillator strengths calculated by Schiffetal. Using the Born approximation we calculate generalized oscillator strengths and integrated cross sections from threshold up to 5 keV for the electron impact excitation of the resonance transition 11S–21Pin the helium isoelectronic sequence. The accuracy and the systematics of the results are discussed.

ISSN:0021-8979    

DOI:10.1063/1.328597

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The uniaxial stress‐induced coupling of the optical ordinary and extraordinary modes in CdS is quantitatively investigated by analyzing, at room temperature, the transmitted light spectrum of a sample placed between two polarizers crossed along the natural neutral lines. Experiments are performed in the wavelength range 5200–7000 A˚ under application of a calibrated (<500 bar) uniaxial stress directed at 45° with respect to the C axis. At the near gap isotropic wavelength 5229 A˚ the phase matching allows energy transfer. It is shown that the high selectivity of the process is due to the fast rotation of the induced neutral lines. Due to the stress‐induced splitting, the actual birefringence exhibits a sharp but nonzero minimum, at the isotropic wavelength, which is a linear increasing function of the pressure. Its linear pressure coefficient is measured, 6.3×10−6bar−1, and this allows a direct calculation of the corresponding elasto‐optic coefficientp44= 9.9×10−2. The frequency dispersion ofp44is investigated near the fundamental absorption edge where it exhibits a broad maximum and a sharp structure. The main characteristics of a coupled mode band‐pass optical filter are calculated and briefly discussed. Finally the residual internal strain field in most ’’as‐grown’’ crystals is estimated as 1.5×10−5.

ISSN:0021-8979    

DOI:10.1063/1.328598

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Experimental results of small‐signal gain in CO chemical laser, operating with very high values of CS:CS2and S:CS, are presented. The laser is produced in a shock tunnel where complete thermal dissociation of CS2into CS+S is accomplished by a reflected shock wave. The dissociated products, diluted in Ar, expand through a supersonic nozzle into a combustion chamber, where molecular oxygen is supersonically injected. The two streams react, and vibrationally excited CO is produced. The experimental data are compared with a numerical model developed for this laser. A fairly good agreement between calculations and experiments was found, which enables the utilization of the mathematical model for better understanding of the processes involved in laser operations. Gains for P7(14) and P5(18) were measured at distances of 5.5 and 11.5 cm downstream from oxygen injectors. Stagnation pressure of 25 atm was kept constant in all experiments. Stagnation temperatures were varied in the range of 2500–4600 °K, and mixtures of CS2:Ar between 5:90 and 30:70 were tested. A maximum of small‐signal gain was observed for each of the parameters investigated. The maximum gain measured for P7(14) was 8% cm−1for CS2:Ar = 20:80 and stagnation temperature of 4000 °K. For these operating conditions, laser oscillations were observed in an 8‐cm‐long active cavity. The resonator consists of a full reflector and a 42% reflective coupling mirror.

ISSN:0021-8979    

DOI:10.1063/1.328599

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Laser chemical vapor deposition (LCVD) uses a focused laser beam to locally heat the substrate and drive the CVD deposition reacton. Several different deposition reactions and substrates have been examined as a function of intensity and irradiation time using a CO2laser source: Ni on SiO2, TiO2on SiO2, TiC on SiO2, and TiC on stainless steel. LCVD film thicknesses range from <100 A˚ to ≳20 &mgr;m. Deposition rates of mm/min have been observed for LCVD Ni and 20 &mgr;m/min for LCVD TiO2. The diameter of the deposited films is dependent on irradiation conditions and can be as small as one tenth of the laser beam diameter. The LCVD films exhibit excellent physical properties such as adherence, conductivity, hardness, and smoothness.

ISSN:0021-8979    

DOI:10.1063/1.328600

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Measurements were made of the light scattered out of the Corning 7059 glass thin‐film optical waveguide sputtered onto substrates of pyrex glass. The angular distributions of the scattered light can be explained by the waveguide imperfections not only of surface roughness of air‐film‐substrate interfaces but of refractive‐index inhomogeneities. The measured scattering patterns are consistent with the theory taking account of both imperfections, assuming a correlation length ofbx/&lgr; ∼ 0.05 andbz/&lgr; ∼1.0, wherebxandbzare the correlation lengths in the directions perpendicular and parallel to the waveguide surface.

ISSN:0021-8979    

DOI:10.1063/1.328601

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The generation of acoustic harmonics by nonlinear dislocation motion is studied using several models in which the dislocations are initially bound in asymmetric potential wells from which they mas escape at large amplitudes of vibration. The models are the edge dipole, the glide loop stabilized by a center of dilation, and variants of these, each subjected to a sinusoidal stress of circular frequency &ohgr; = 2&pgr;×22.5×103s−1; in each case inertia‐like terms were negligible at this frequency. For each model we found the steady‐state response by numerical integration. The corresponding dislocation strain was expressed as a Fourier series, thenth term having the formAnsin(n&ohgr;t−&fgr;n). We obatined the variation of theAnas a function of the amplitude of the vibrational stress. Certain features are common to all the solutions: (i) for dislocations trapped in a potential wellAn∝An1; (ii) on escape from a well at higher amplitudes there is a peak inAn/A1and a sharp fall inAn/An1; (iii) a change in the effective symmetry of the motion on escape is reflected in a change in the relative proportions of even and odd harmonics. Our results are not inconsistent with the previous theoretical work. Comparison with the available data, although hampered by the lack of a really complete set, indicates that such behavior is observed. These patterns are expected only at fairly low values of &ohgr;, such that the damping force does not overshadow the dislocation restoring force.

ISSN:0021-8979    

DOI:10.1063/1.328637

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We have developed a model for use in ion‐driven inertial confinement fusion (ICF) target design to describe the deposition of energy by an arbitrary ion traversing a material of arbitrary composition, density, and temperature. This model particularly emphasizes the deposition physics of light ions having specific energies of 3 MeV/amu or less. However, the model is also applicable to heavy ion fusion problems where there are specific energies in excess of 10 MeV/amu. We have found that an accurate description of the cold material stopping power must include both shell corrections to the Bethe theory as well as the alternative LSS (Linhard‐Scharff‐Schio&slash;tt) model at low energies. We have incorporated finite temperature effects by scaling the relevant bound electron parameters with the degree of material ionization as well as by including the free‐electron stopping power. We discuss both the phenomenon of range shortening and range relengthening in heated material. Our preliminary calculations indicate that the minimum ion range in heated material is approximately one‐half that in cold dense targets, independent of the identities of the projectile ion and the host material.

ISSN:0021-8979    

DOI:10.1063/1.328602

出版商:AIP    

年代:1981

数据来源: AIP