bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of layered crystals of titanium silver
Authors: Zheng J. Q. , Ketterson J. B. , Felcher G. P.
Published: February 2003

Synthetic crystals of layered titanium silver were grown epitaxially by vapor deposition techniques. The motivation was to generate a one-dimensional diffraction grating to be used as a soft x-ray monochromator. The structural analysis shows that the as-grown film is almost a single crystal, where a new phase is present, characteristic of the layering process. The results indicate that it is now becoming feasible to produce new synthetic crystals by vapor deposition of two chemically quite dissimilar metals.
Comments on Zn3P2 band structure
Authors: Pawlikowski Janusz M.
Published: February 2003

Recent optical and photoelectric data of Zn3P2 single crystals are reviewed including measurements of oriented crystals under polarized light. A Zn3P2 band-structure model is proposed which is based on these results. The influence of tetragonal crystal structure is included in the model as the additional split-off valence level and two different minima in the conduction band near the Γ point.
Modeling of a CO chemical laser produced by supersonically mixing CS/S with O2
Authors: Tilleman M. M. , Stricker J.
Published: February 2003

A computer model of a CO chemical laser produced by supersonic mixing of CS/S with O2 is presented. The model has been shown to accurately predict measured gain coefficients of P7(14) and P5(18) lines, hence it was utilized for further parametric studies leading to a better understanding of the processes involved in laser operation. The model predicts high gain and high specific available energy in v = 1→0 to v = 20→19 transitions. A maximum gain was obtained for each of the parameters investigated. For certain operational conditions, complete population inversion was observed.
Self-consistent solution for spatial hole burning in stripe geometry InGaAsP/InP double heterojunction lasers
Authors: Yano Mitsuhiro , Ishikawa Hiroshi , Takusagawa Masahito
Published: February 2003

This paper presents a study of spatial hole burning in the carrier concentration distribution of stripe geometry InGaAsP/InP double heterojunction lasers emitting at 1.3 μm. To study the behavior in detail we took the mutual relationships between the current flow in the resistive layer, the junction voltages between the active and confining layers, and the carrier concentration distribution in the active layer into consideration. Moreover, we treated the InP/InGaAsP/InP double heterojunction through an analysis of the heterojunction energy band structure. The analysis demonstrated that in narrow-stripe lasers (?7-μm stripe width) spatial hole burning in the carrier concentration distribution is greatly suppressed even at twice the threshold. We found the existence of a self-focusing current flowing into the center of the stripe that acted to suppress spatial hole burning. The results suggest that in the quaternary lasers—the property of the active layer crystal, for example—long intraband relaxation time contributes greatly to the longitudinal-mode behavior.
Nondestructive evaluation of planar defects in plates using low-frequency shear horizontal waves
Authors: Fortunko C. M. , King R. B. , Tan M.
Published: February 2003

An ultrasonic technique is described that allows the determination of the through-thickness dimension and limited localization of planar defects (cracks) in an isotropic metal plate. The scattering of horizontally polarized shear (SH) plate waves by edge and buried planar defects is investigated using a variational integral expression. Numerical results are presented that allow the calculation of the SH plate wave signal amplitudes as a function of defect through-thickness dimension and location within a plate for two-dimensional cracks. It is shown that SH waves are particularly useful for detecting and sizing of crack-like defects. In addition, it is demonstrated that in plates, which can support a number of propagating SH plate waves, it is also possible to determine the relative position of a defect from interference phenomena. The numerical results are confirmed experimentally using an electromagnetic-acoustic transducer system to generate and detect 454-kHz SH wave signals along the normal to the circumference of a 1.22-m-diam steel pipe with a 15.9-mm wall thickness. The experimental results demonstrate the efficacy of using SH wave signals in quantitative nondestructive evaluation of butt welds.
Hydrogen vibrational population distributions and negative ion concentrations in a medium density hydrogen discharge
Authors: Hiskes J. R. , Karo A. M. , Bacal M. , Bruneteau A. M. , Graham W. G.
Published: February 2003

The vibrational population distribution for hydrogen molecules in a hydrogen discharge has been calculated taking into account electron collisional excitation, molecule-molecule, and wall collisional de-excitation processes. Electronic excitation processes include vibrational excitation by 1 eV thermal electrons acting through the intermediary of the negative ion resonances, and vibrational excitation caused by the radiative decay of higher singlet electronic states excited by a small population of 60 eV electrons in the discharge. The molecules are de-excited by molecular collisions transferring vibrational energy into translational energy, and by wall collisions. The distributions exhibit a plateau, or hump, in the central portion of the spectrum. The relative concentration of negative ions is calculated assuming dissociative attachment of the low temperature electrons to vibrationally excited, non-rotating molecules. The ratio of negative ions to electrons in the discharge is calculated to be of order 1% if the vibrational excitation survives no more than one wall collision, and of order 10% if the excitation survives ten collisions. The possibility is considered that the higher concentrations can be achieved with few wall collisions provided dissociative attachment occurs to highly rotating molecules.
Study of electron waves in electrical discharge channels
Authors: Jurenka H. , Barreto E.
Published: February 2003

The fast luminous pulses experimentally observed to propagate in electrical discharge channels, and believed to have a significant role in the process of electrical breakdown, are investigated, using a plasma fluid approach. These pulses fall in two regimes characterized by different average velocities of 106 and 108 m/s. We concentrate on the lower velocity pulses. A nondimensional analysis is used to show that these waves can be considered as longitudinal electron fluid waves driven by electron pressure gradients in weakly ionized plasmas. Model equations are derived considering each additional term in the momentum equation as a small but finite perturbation. In all cases, standard nonlinear fluid model equations are obtained as possible solutions. Electric forces lead to the Korteweg-deVries equation, viscosity to Burgers equation, and electron-neutral collisions to a damped wave equation. The propagation and attenuation of fluid waves along preionized channels is naturally associated with the formation of steps. It is suggested that thermalization must be associated with the injection of electrons from a source external to those in the preionized channel.
Formation of CN− radicals by sequential implantation of carbon and nitrogen ions into KCl
Authors: Metz W. A. , Thomas E. W.
Published: February 2003

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 direct in situ determination 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 3.4×10−21 cm3 in 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.
Lateral-wave studies in a model lithosphere
Authors: Brown M. F. , King R. W. P. , Wu T. T.
Published: February 2003

An experimental basis is provided for the theoretical expressions associated with the Eρ lateral-wave field due to a horizontal dipole in a conducting half-space of sea water. Both perturbed and unperturbed fields are studied in detail in a laboratory model of the lithosphere. It is found that rectilinear and wedge-shaped discontinuities at the air-water interface comprise effective perturbations of Eρ, while submerged metallic cylinders do not. The effective perturbations, localized in their effect on the overall propagation of the lateral wave over several wavelengths, have geometries chosen to characterize the broad plateaus and mountains of a real lithosphere.
Focusing experiments with an inverse reflex tetrode
Authors: Pershing D. E. , Golden J. , Pasour J. A. , Kapetanakos C. A.
Published: February 2003

The focusing properties of an Inverse Reflex Tetrode (IRT) used for ion beam generation have been investigated experimentally. Focusing is achieved by replacing the planar (0°) electrodes of a standard IRT with moderately inwardly tapered electrodes (7.5, 10, and 15°). The greatest degree of focusing is obtained with the 15° electrodes as determined by beam profile measurements using streak photography and nuclear activation techniques at various axial target positions. A scissoring effect is observed, due to temporal variations in generator voltage and current, that is manifested by an axial variation in the focal point with time. Calculations of proton trajectories confirm the experimental results and demonstrate the importance of self-fields within the A-K gap in determining the characteristics of an ion beam generated by an IRT.
Discharge parameters of a high-pressure, ultraviolet-preionized, transversely excited CO2 laser
Authors: Midorikawa K. , Wakabayashi K. , Nakamura K. , Obara M. , Fujioka T.
Published: February 2003

Discharge parameters have been investigated experimentally and theoretically for a high-pressure, ultraviolet-preionized, transversely excited CO2 laser. The theoretical model including the excitation circuitry is presented which predicts the discharge performance at pressure ranges of 2–10 atm in a satisfactory manner. The operating E/N and discharge impedance in a quasi-steady field were studied by accurately measuring the voltage-current waveforms; E is the electric field strength and N the gas number density. The electron transport coefficients have been found to be a function of the pressure versus the change of the measured voltage waveforms relating to that pressure. The theoretical results treating the transport coefficient as a function of the pressure were in very good agreement with the experimental results.
Signal and noise in magneto-optical readout
Authors: Mansuripur Masud , Connell G. A. N. , Goodman Joseph W.
Published: February 2003

For a magneto-optical readout system which uses the Kerr effect, the power spectral density of the read signal has been derived. The noise components originating in the photodetection and amplification stages appear as additive terms in the expression for the overall spectral density, enabling us to define a signal to noise ratio for the readout system. Adjustable parameters of the system are then optimized and a multilayer disk structure is introduced which enhances the Kerr effect and, consequently, results in an increased signal to noise ratio.
The geometry and permittivity of snow at high frequencies
Authors: Colbeck S. C.
Published: February 2003

The geometry and porosity of dry snow varies widely depending on the history of conditions. The permittivity of dry snow increases with increasing ice content but is not greatly affected by the shapes of the ice particles. In wet snow the permittivity increases with liquid content and the geometry is very important. However, the liquidlike layer has little effect on permittivity. The permittivity is described using Polder and van Santen’s mixing formulae and approximations of the geometries at high and low liquid contents. It is shown that the common assumption of liquid shells over ice spheres is both physically incorrect and leads to large errors.
On the upper state formation kinetics and line tunability of the iodine monofluoride discharge laser
Authors: Dlabal M. L. , Eden J. G.
Published: February 2003

The collisional kinetics of upper state formation for the iodine monofluoride (IF) discharge pumped laser have been studied using tunable dye laser absorption spectroscopy. As for electron- beam excitation, the immediate precursor to IF*(D′) is found to be the I*(6s4P) species. Energy stored in the F*(4P) states, however, is not recovered in the laser’s output due to weak F*→I* collisional coupling. Limited tunability of this laser has been demonstrated with a Littrow prism and has resulted in the observation of a new D′→A′laser transition at 467 nm.
Secondary ion mass spectrometry study of lightly doped p-type GaAs films grown by molecular beam epitaxy
Authors: Clegg J. B. , Foxon C. T. , Weimann G.
Published: February 2003

Lightly doped p-type GaAs films grown by molecular beam epitaxy on Cr-doped substrates have been chemically analyzed using dynamic secondary ion mass spectrometry. Residual levels of Cr are, in general, below 4×1013 cm−3. A major source of impurities in such material is identified. The effect of substrate temperataure on the concentration of B, Mg, Al, Si, Ca, Cr, Mn, Fe, and Cu are reported, and their likely effect upon the minority carier properties of the layers is discussed.
Saturation of far-infrared photoconductivity in n-GaAs
Authors: Brown Fielding , Link Lee , Platt Stephen
Published: February 2003

The photoconductivity of epitaxial n-GaAs (n = 2.6×1014 cm−3) has been measured in response to high intensity (P∼2.4 kW/cm2) radiation at λ = 95 μm. The saturation curve of photoconductivity versus excitation power yields a recombination time of 10−8 s, which is much shorter than the value predicted, 10−6 s, by the theory of the electron-phonon interaction. Recombination appears to occur from localized states as well as by capture of free conduction band electrons.
Stress modulated photoelectrochemical spectroscopy
Authors: Handley L. J. , McCann J. F. , Haneman D.
Published: February 2003

A relatively simple stress modulation technique, based on optical absorption, for measuring the interband transitions in semiconductor electrodes in electrolytes is described. The modulated stress is applied to the semiconductor by modulating the strain of an attached piezoelectric transducer. Stress modulated photoelectrochemical spectra in the vicinities of the minimum interband gaps of an n-TiO2 single crystal electrode and a thin-film n-CdSe electrode in situ are presented.
Magnetization of RFe3 intermetallic compounds: Molecular field theory analysis
Authors: Herbst J. F. , Croat J. J.
Published: February 2003

We report magnetization measurements of all RFe3 intermetallic compounds known to form (R = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm). A two-sublattice molecular field model is employed to analyze the data except in the case of YFe3, for which one magnetic sublattice is assumed. In general, the model adequately describes the temperature dependence of the magnetization. For SmFe3 our results suggest that the samarium and iron moments are ferromagnetically coupled.
Numerical evaluation of the dielectric polarization distribution from thermal-pulse data
Authors: Mopsik F. I. , DeReggi A. S.
Published: February 2003

A method for numerically carrying out the Fourier analysis for the thermal-pulse experiment is given. It is shown that it is possible to obtain the polarization distribution across the thickness of a thin film (25 μm) to within the limits set by the experimental data. For such films, resolution of the distribution to within 0.1 of the film thickness is possible. Results are given for the experiment by using a charge measurement rather than a voltage measurement. The effect of a finite-width pulse is shown to cut off the Fourier coefficients in such a way as to smooth any distribution. Pulsing the sample alternately on both sides is shown to greatly increase the resolution of the experiment. Results for a PVF2 film and a P(VF2-TFE) copolymer film show that interesting details can be found by the experiment.
Tailoring stimulated emission cross sections of Nd3+ laser glass: Observation of large cross sections for BiCl3 glasses
Authors: Weber M. J. , Ziegler D. C. , Angell C. A.
Published: February 2003

The stimulated emission cross sections of rare-earth transitions depend strongly on the host. The properties that influence the cross sections—line strength, linewidth, and refractive index—are reviewed, and rules for tailoring cross sections are discussed. To illustrate the application of these rules, the largest stimulated emission cross section for the 4F3/2→4I11/2 transition of Nd3+ observed for any oxide or halide glass was obtained for a new class of bismuth-chloride-based glasses. Spectroscopic and physical properties and laser parameters of these and other halide glasses are presented.
Photoluminescence investigation of residual shallow acceptors in AlxGa1−xAs grown by metalorganic vapor phase epitaxy
Authors: Mircea-Roussel A. , Brière A. , Hallais J. , Vink A. T. , Veenvliet H.
Published: February 2003

Low-temperature photoluminescence on metalorganic vapor phase epitaxial AlxGa1−xAs layers (0⩽x⩽0.37) exhibiting relatively sharp bound exciton and band acceptor lines, combined with effective mass-type calculations of the expected transition energies, has allowed the identification of carbon, zinc, and possibly silicon as residual acceptors. Carbon seems to be the predominant residual acceptor impurity species in layers grown at high temperature. Large spectral shifts in direct-band-gap AlxGa1−xAs as a function of excitation density or in time resolved spectroscopy reported in literature are attributed to the presence of several acceptor species rather than to D-A pair recombination.
Temperature profiles induced by a scanning cw laser beam
Authors: Moody J. E. , Hendel R. H.
Published: February 2003

We present calculations of the temperature profiles induced by a moving cw elliptical laser beam with a Gaussian intensity distribution in a semi-infinite material. Temperature-dependent thermal diffusivity, conductivity, and surface reflectivity are incorporated in our model, and some aspects of melting are discussed. As an example, we apply the calculations to silicon. For a comparison of stationary elliptical spots of varying eccentricities, we present material-independent normalized linear temperature profiles. We find that highly elliptical beams can be used to rapidly scan and anneal large areas.
Spin-polarized photoelectron emission study of AlxGa1−xAs alloys grown by molecular beam epitaxy
Authors: Ciccacci F. , Alvarado S. F. , Valeri S.
Published: February 2003

We report on spin-polarized photoelectron emission and quantum yield measurements performed on AlxGa1−x As alloys (0.08⩽x⩽0.65) which were grown by molecular beam epitaxy and activated in situ to negative electron affinity by exposure to Cs and O2. We investigate the electronic structure of the alloys near the band-gap region. These alloys can be used as high- efficiency spin-polarized photoelectron sources at photon energies matching convenient light sources.
Thermal stability and growth kinetics of Co2Si and CoSi in thin-film reactions
Authors: Tu K. N. , Ottaviani G. , Thompson R. D. , Mayer J. W.
Published: February 2003

We have investigated the growth of Co2Si and CoSi around 400 °C in samples of Si/Co and Si/CoSi/Co. We selected the Co-Si system because CoSi is known to have a larger heat of formation than Co2Si, hence the former should be favorable for formation from the viewpoint of free energy change or driving force. However, we found that Co2Si is the one which always grows first. This leads us to conclude that it is not the driving force but rather the kinetics which governs the selective growth of thin-film intermetallic compounds. Thus, we propose here that the first phase formation is selected by the one with the lowest kinetic barrier.
Magnetic inhibition of insulator flashover
Authors: VanDevender J. P. , McDaniel D. H. , Neau E. L. , Mattis R. E. , Bergeron K. D.
Published: February 2003

Electrical breakdown across a vacuum/plastic interface in the presence of applied or self-generated magnetic fields, B?3.5 T, was investigated. The E×B drift of charged particles near the interface in these experiments was away from the insulator surface. The self-magnetic field effects on a plastic vacuum insulator flashover were examined with inductive loads, particle beam loads, and imploding plasma loads. Average breakdown electric fields of up to 38 MV/m were observed. Power densities of 100 TW/m2 were passed through acrylic-vacuum interfaces. The flashover electric fields were improved over the B = 0 fields from previous experiments by factors of 7.1, 5.0, and 1.8 for the −45°, 0°, and +45° insulators, respectively.
Thermal annealing of implantation strain in bubble garnet films: Stability of ion-implanted propagation devices
Authors: Pierce R. D. , Caruso R. , Mogab C. J.
Published: February 2003

Thermal annealing of damage-induced strain in ion-implanted epitaxial garnet films has been studied. The high strains typical of ion-implanted propagation patterns decrease nearly linearly with the logarithm of annealing time (ln t), a functional dependence characteristic of thermally activated processes with a broad spectrum of activation energies. The theory of Vand, as extended by Primak, satisfactorily describes the data. In as-implanted material, significant relaxation of the implantation strain is predicted for a device operating at 125 °C for several years. However, a stabilizing anneal for 30 min at 325–350 °C is adequate to assure 99% stability for 20 years at 125 °C. The required anneal is consistent with current design and fabrication practices.
A comparison of spectroscopic and Thomson scattering measurements of electron densities and temperatures in a transient expanding plasma flow
Authors: Heidrich J. E. , Jacoby B. A. , York T. M. , Robinson J. W.
Published: February 2003

The expansion flow of helium plasma in the end loss region of a theta pinch has been studied. The accuracy of several spectroscopic techniques for determining plasma properties in the transient, inhomogeneous plasma has been evaluated. Plasma at a location of 2.5 cm outside the end of a 25- cm long theta-pinch coil is characterized by Ne ∼1016 cm−3, Te ∼6 eV. Radial electron density profiles were obtained by: (1) Abel inversion of plasma continuum emission from chords across the plasma column to produce relative radial electron density profiles, with normalization by a new technique, whereby a theoretical He II 4686-Å spectral profile is calculated and compared to that observed experimentally being emitted across the diameter of the plasma column; and (2) direct prediction of an absolute electron density profile by Abel inversion of He II 4686-Å spectral profiles obtained by viewing chords across the plasma column. Electron temperatures were obtained from spectroscopic measurements across the diameter of the plasma flow by: (1) measurement of the ratio of the He II 4686-Å line intensity to the underlying continuum intensity; and (2) measurement of the absolute intensity of the He II 4686-Å line. The accuracy of these spectroscopic techniques in a pulsed discharge, with plasma undergoing flow expansion, will be indicated by comparison of the results with those from Thomson scattering.
Studies of the anode region of a high-intensity argon arc
Authors: Sanders N. , Etemadi K. , Hsu K. C. , Pfender E.
Published: February 2003

This paper is concerned with experimental and analytical/numerical studies of the anode region of an atmospheric pressure argon arc in a current range from 100 to 300 A. The arc arrangement allows unobstructed viewing of the entire anode region, including the anode itself, and it is also suitable for simulating short as well as long arcs. Depending on the flow situation in the anode region, two different types of stable arc roots are observed. The diffuse anode arc root, characterized by a strong flow impinging on the anode surface, is well known from free-burning, short arcs. The second type reveals a more or less vevere constriction in front of the anode, caused by the entrainment of gas into the arc, resulting in an anode jet. Measurements of the induced flow at the cathode of such an arc show a linear increase of the induced mass flow rate with increasing current. This correlation can be confirmed by a simple analysis. A fast-scanning, computer-controlled system has been used for spectrometric measurements of the temperature distribution for both modes of anode arc roots, assuming local thermodynamic equilibrium (LTE) in the arc. The maximum temperatures in the arc core compare favorably with calculated temperature distributions of the constricted mode. The calculated isotherms, however, show a substantial shift which is probably due to the chosen boundary conditions at the end of the constrictor tube.
Photoinduced current transient spectroscopy of semi-insulating InP:Fe and InP:Cr
Authors: Rhee Jin K. , Bhattacharya Pallab K.
Published: February 2003

Traps in semi-insulating InP:Fe and InP:Cr have been studied by Photo-Induced Current Transient measurements for the first time. Hole emissions to the valence band with activation energy ΔET = 0.69±0.01 and 0.96±0.01 eV from the Fe and Cr levels, respectively, have been identified. These values of ΔET , on comparison with Hall measurement data for 350⩽T⩽600 K, indicate negligible coupling of the Fe and Cr levels with the lattice. Electron traps with ΔET = 0.68±0.01 eV, probably related to native defects, and hole traps with ΔET = 0.50±0.005 and 0.67±0.01 eV have also been detected. The thermal capture cross section related to the various electron and hole emissions have been estimated.
Temperature dependence of the conductivity due to direct interband transitions in p-Si
Authors: Vindevoghel J. , Vindevoghel M.
Published: February 2003

Theoretical calculations of the conductivity due to free carriers’ direct transitions between the three valence bands of p-Si are performed starting from Kane’s theory and taking their warped character into account. First experimental results concerning the variation of the conductivity of p-Si versus the frequency are reported in the limited range of frequencies 0–250 cm−1, the temperature being a parameter varying from 293 to 173 °K. In this range of frequencies, an accurate determination of the relaxation part of the conductivity allows to measure quantitatively the contribution of the transitions between the heavy and the light holes bands. Using a value of the spin-orbit energy Δ = 0.035 eV and values of the band parameters L = −6.69, M = −4.56, N = −8.50 (h/2/2m units), these partial experimental results are in good agreement with the theoretical ones for frequencies up to 250 cm−1. Nevertheless, important discrepancies must be expected at higher frequencies.
The dependence of transversely excited atmospheric CO2 laser performance on circuit configuration
Authors: Cridland J. V. , Howells S.
Published: February 2003

The dependence of pulsed CO2 laser performance, in terms of efficiency and power output, on circuit configuration has been investigated. It has been shown that the type of circuit used to excite the laser can significantly affect its performance. The variation of laser output with circuit has been shown to be consistent with a change in the value of E/N at which energy is transferred into the glow discharge.
Plasma conditions required for attainment of maximum gain in resonantly photo-pumped aluminum XII and neon IX
Authors: Apruzese J. P. , Davis J. , Whitney K. G.
Published: February 2003

We present a detailed analysis of the plasma conditions required to optimize gain in two proposed x-ray lasing schemes using resonant photo-pumping. In one proposed configuration, the Si XIII line 1s2-1s2p1P at 6.650 Å pumps Al XII 1s2−1s3p1P at 6.635 Å, inverting the Al XII n = 3 and n = 2 levels which are separated by 44 Å. A similar approach which utilizes the Na X 1s2-1s2p1P line at 11.00 Å would invert the n = 4, 3, and 2 levels of Ne IX. Conditions in the pumped neon and aluminum plasmas, and in the pumping silicon plasma, are calculated using a multistage, multilevel atomic model with multifrequency radiation transport. For modeling the pumping sodium line we have inferred the intensity from a spectrum of a neon filled, laser-imploded glass microballoon containing sodium impurities obtained at Rochester. The pump line intensities calculated for Si and inferred for Na are equivalent to blackbodies of 252 and 227 eV, respectively. It is found that peak gain for the 3-2 lines of about 100 cm−1 occurs at ion densities of 1020 cm−3 and 4×1020 cm−3 in the pumped neon and aluminum plasmas, respectively. Temperatures required to maximize gain in the pumped plasmas are found to be 50 and 100 eV, for neon and aluminum, respectively. Finally, since the silicon and aluminum lines are slightly off resonance, we have investigated the effect of streaming the plasmas toward each other at various velocities to offset some or all of the wavelength difference. It is found that a streaming velocity of 6.8×107 cm sec−1—fully offsetting the wavelength difference—will approximately triple the achieved gain compared to the zero velocity case. Lesser increases in gain occur with partial velocity offsets.
The coupling of continuous-wave laser radiation into painted aluminum-alloy plates
Authors: McLachlan A. D. , Whitbourn L. B.
Published: February 2003

This paper describes a model for the physical behavior of a painted surface when irradiated by a high-energy laser. The model proposes that the paint degrades to a residue which adheres to the surface and whose optical and thermal properties control the coupling of the radiation to that surface Experimental observations are presented which confirm the theoretical predictions of the model. Measurements of the intensity-dependent absorptance of the surface of painted A12024 alloy plates agree with calculated values when appropriate values of the thermophysical properties of the paint residue are chosen.
Non-Newtonian viscous flow in glass
Authors: Simmons Joseph H. , Mohr Robert K. , Montrose C. J.
Published: February 2003

The viscosity of a soda-lime silica glass was measured at high strain rates. The data show non-Newtonian viscous flow in this inorganic oxide glass with the viscosity values below the expected Newtonian value. Following the imposition of large, steady strain rates, the observed stress increases with time to a maximum and then decreases to a time-independent value. A comparison of the viscosity behavior of this glass with the molecular dynamics results in a ’’Lennard-Jones’’ glass shows a number of points of correspondence and suggests the interpretation of the non-Newtonian behavior as resulting from structural rearrangements in the material. The combined data show that the sustained, steady-state stress asymptotically approaches a maximum at very high strain rates. This limiting stress is interpreted as the actual cohesive strength of the material and is calculated to be 1.4×108N/m2 (20,000 psi) for the glass under study.
Extensional vibrations of rectangular crystal plates
Authors: Lee P. C. Y. , Nakazawa M. , Hou J. P.
Published: February 2003

A system of one-dimensional equations governing the extensional (contour) modes of vibrations in rectangular crystal plates is derived from the Cauchy–Voigt two-dimensional equations of extensional motion of anisotropic, elastic plates. The system of equations is further divided into two groups of equations governing, separately, the symmetric (contour extensional) and antisymmetric (contour shear) modes of vibrations, by setting the elastic stiffness coefficients γ15 = γ35 = 0 in order to neglect the coupling effect between the two groups. Closed form solutions of contour extensional vibrations are obtained for rectangular crystal plates satisfying the traction-free conditions at four edges. Dispersion relation and frequency equation are obtained in explicit form for the first three contour extensional modes. Resonance frequencies, for various contour extensional modes, are computed as a function of the length-to-width ratio (a/c) of plates. Predicted results are compared with the detailed measurements for rectangular GT cuts with close agreement. Two-dimensional vibration patterns have also been calculated at resonances for different values of a/c ratio.
Measurements with cylindrical Langmuir probes in a supersonic equilibrium plasma
Authors: Rosenbaum M. , Louis J. F.
Published: February 2003

Experimental results are presented from negatively-biased cylindrical Langmuir probes located in a magnetohydrodynamic (MHD) generator with the flow supersonic and the plasma both in equilibrium and uniform. Voltage-current characteristics were obtained over a wide range of bias voltages, up to the arcing limit, and these showed that the probes operate in the convection-sheath mode. Electron densities deduced from the probe measurements are in agreement with values obtained by other methods; the results confirm the applicability of the Langmuir probe as a diagnostic technique in flowing plasmas.
The Pierce instability in neutralized inertial confinement fusion ion beams
Authors: Lemons Don S. , Cary John R.
Published: February 2003

The stability of a charge and current neutralized electron-ion beam propagating between two planar boundaries is investigated. For equipotential boundaries the beam is, as originally shown by Pierce, electrostatically unstable for electron current densities above a certain limiting value. If, however, the electric field at the upstream boundary is required to vanish, there is no instability. An intermediate case, in which the two boundaries are electrically connected with a finite conductivity plasma, corresponds to the proposed use of neutralized light and heavy ion beams for inertial confinement fusion drivers. Results indicate such beams can propagate either stably or with zero-frequency Pierce instability growth rates which are probably insignificant. lectric currents; boundary conditions; current density; electric fields; plasma;
Measurement of thermal diffusivity using a pyroelectric detector
Authors: Yeack C. E. , Melcher R. L. , Jha S. S.
Published: February 2003

A new method of measuring the thermal diffusivity of thin layers has been developed and applied to the characterization of laminated structures. The thermal diffusivity is measured using pyroelectric detection of a laser generated thermal pulse propagating through the sample. The shape of this pulse is governed by the thermal properties of both the sample and the detector. However, the thermal diffusivity of the sample can be determined from the position of the peak in the pyroelectric signal and the sample thickness. This method can be applied to thermal diffusivity measurements of thin or thick films, laminates, and thermal greases.
Motional side-band resonances in the microwave spectrum of stored ions
Authors: Lakkaraju H. S. , Schuessler H. A.
Published: February 2003

Side-band resonances were investigated in the radio-frequency (rf) spectrum of free ions stored in a radio-frequency quadrupole ion trap. The magnetic resonance signals occur at the center frequency and at the center frequency plus or minus integral multiples of the characteristic ion macromotion frequencies. The experiment was performed on 3He+ using the ion storage exchange collision technique. Contributions of the side-band intensity arose predominantly from the standing microwave field inside the cavity. The effect of a small traveling wave component was also included. The microwave field was fed into the trap structure which, in addition to being used for trapping, was also employed as a broad band cavity in the TE013 mode. The dependence of the intensity distribution of the side-band spectrum on different ion motion temperatures and energy distributions of the ions was studied numerically. It was demonstrated experimentally that initially the stored ions have a uniform energy distribution. Since the stored ion cloud samples different microwave fields at different times, the induced perturbation of the microwave field is spread out in frequency and a correlation function approach is suitable to interpret the side-band spectra. The present experiment was carried out in the microwave region where narrow-band coherent radiation fields are readily available. However, the same side bands should also occur in the optical spectrum of stored ions and are of interest to laser cooling experiments.
Motion of ions in the Kingdon trap
Authors: Lewis R. R.
Published: February 2003

The classical and quantum motion of ions in a Kingdon trap (Orbitron) is studied for nearly circular orbits. The frequencies of small axial and radial oscillations are derived for both the logarithmic potential and the actual potential. A numerical comparison with the asymptotic approximation and with exact energy eigenvalues shows that the small oscillation method is adequate for most purposes.
Magnetic induction of ferromagnetic spherical bodies and current bands
Authors: Brown Samuel H. , Baker F. Edward
Published: February 2003

The method of separation of variables has been applied to derive the magnetic fields of four magnetostatic field problems. Three problems consist of infinitesimally thin spherical current bands and a ferromagnetic spherical shell. Two of these configurations have a magnetic spherical shell with an internal or external current band and the third has a spherical shell with both internal and external current bands. A fourth problem consists of a magnetic sphere with an external current band of finite width. Calculations of the magnetic field for sample problems are presented. The solutions are intended for analysis of the magnetizing behavior of ferromagnetic substances and have applicability in electrical machinery and magnet design.
Longitudinal mode self-stabilization in semiconductor lasers
Authors: Kazarinov R. F. , Henry C. H. , Logan R. A.
Published: February 2003

A general mechanism of self-stabilization of longitudinal modes in semiconductor lasers is presented. The stabilization is due to the modulation of the inverted population by the beating of the fields of lasing and nonlasing modes, thereby modulating the rate of stimulated emission. This leads to two optical nonlinearities: one causing gain suppression of nonlasing modes and the other causing coupling of pairs of nonlasing modes that are equally separated from the laser line. The two nonlinearities nearly cancel, but their net effect is a weak suppression of the nonlasing modes and stabilization of the lasing mode. Buried optical guide lasers were stabilized in a single longitudinal mode for currents greater than 6mA above threshold. The mode intensity spectra of the lasers were measured over 5 decades and converted to gain spectra, which could be compared with the theory. The gain spectrum is parabolic at threshold. At 20 mA above threshold it remains continuous at the laser line but narrows and becomes structured. The structure is characterized by a dip in the gain and in the mode intensities occurring about 3 modes from the laser line. The laser line also causes a pronounced dip in the gain spectra of the nonlasing first order transverse modes. All of these features can be approximately accounted for by the theory.
Ultrasonic anomalies in the spectrum of acoustic waves diffracted by periodic interfaces
Authors: Jungman Alain , Adler Laszlo , Quentin Gerard
Published: February 2003

The energy distribution of elastic waves reflected from corrugated periodic solid surfaces is investigated. Broadband pulse echo experiments using ultrasonic spectroscopy are carried out for surfaces with a triangular profile. Sharp discontinuities observed in the received spectrum are interpreted as anomalies first introduced by R. W. Wood [Philos. Mag. 4, 396 (1902)]. These minima are identified as the mode-converted signals along the interface with bulk or surface wave velocities. The observed anomalies may be used to characterize interfaces and quality of bonding.
Misfit dislocations in InP/InGaAsP/InP double-heterostructure wafers grown by liquid phase epitaxy
Authors: Yamazaki Susumu , Kishi Yutaka , Nakajima Kazuo , Yamaguchi Akio , Akita Kenzo
Published: February 2003

The behavior of misfit dislocations in InP/InGaAsP/InP double-heterostructure wafers grown by liquid phase epitaxy has been investigated by x-ray and photoluminescence (PL) topography. Misfit dislocations were found to be generated from the edges of all the wafers studied here. X-ray topographs for angle-polished wafers show that misfit dislocations exist within the upper InP layer and are located in close vicinity to the heterointerface. PL topography has been used to determine the misfit dislocation-free area within the wafers. This area decreases monotonically with the increase of the upper InP layer thickness, and is almost independent of the quaternary layer thickness. The lattice misfit is necessary to be in the range 0∼−0.08% at room temperature for making the area without misfit dislocations as wide as possible. Generation of misfit dislocations is considered to be strongly related to the ’’melt back’’ of the InGaAsP edge growth.
Isolation of instability in the Fredholm integral equation of the first kind: Application to the deconvolution of noisy spectra
Authors: Price G. L.
Published: February 2003

The numerical solution of the Fredholm integral equation of the first kind is formulated so that the source of instability is identified and can be isolated. The problem is regarded as a minimization with no constraints on the solution. It is shown that the introduction of instability depends on the path taken from the initial to the final estimate of the solution. The initial estimate is the given data, and the path which avoids instabilities is that which requires monotonic variation of these data. The method is applied to the deconvolution of noisy spectra and a more objective procedure results than has been previously obtained. Detailed applications and comparisons with previous methods are given.
A radial ion diode for generating intense focused proton beams
Authors: Johnson D. J. , Burns E. J. T. , Farnsworth A. V. , Leeper R. J. , Quintenz J. P. , Bieg K. W. , Dreike P. L. , Fehl D. L. , Freeman J. R. , Perry F. C.
Published: February 2003

A magnetically insulated light ion diode which has produced an ion beam with total current exceeding 400 kA for 25 ns and generated a proton current density approaching 500 kA/cm2 is described. This intense beam current is achieved in a noncurrent neutralized mode via geometric focusing and a balance between self-magnetic field and space-charge forces. A number of techniques are described which have been used to diagnose the beam production, transport, and focusing. These include observation of Kα emission due to beam-induced atomic excitation, prompt-γ radiation due to beam-induced nuclear reactions, and thermal emission due to beam-target heating.
The effect of charge exchange on ion guns and an application to inertial- electrostatic confinement devices
Authors: Baxter D. C. , Stuart G. W.
Published: February 2003

In 1967, R. L. Hirsch [J. Appl. Phys. 38, 4522 (1967)] reported neutron production rates of 1010 neutrons per second from an electrostatic inertial confinement device. The device consisted of six ion guns injecting deuterium or a mixture of deuterium and tritium ions into an evacuated cathode chamber at 30–150 keV. No previous theoretical model for this experiment has adequately explained the observed neutron fluxes. A new model that includes the effects of charge exchange and ionization in the ion guns is analyzed. This model predicts three main features of the observed neutron flux: Neutron output proportional to gun current, neutron production localized at the center of the evacuated chamber, and neutron production decreasing with increasing neutral background gas density. Previous analysis modelled the ion guns as being monoenergetic. In this study, the ion gun output is modelled as a mixture of ions and fast neutrals with energies ranging from zero to the maximum gun energy. Using this theoretical model, a survey of the possible operating parameters indicates that the device was probably operated at or near the most efficient combined values of voltage and background pressure. Applications of the theory to other devices are discussed.
Bulk stiffnesses of metallic glasses
Authors: Davis L. A. , Yeow Y. T. , Anderson P. M.
Published: February 2003

Determinations of density, Vickers microhardness, Young’s modulus, and Poisson’s ratio are reported for a series of Fe-B glasses, for glassy Fe40Ni38Mo4B18, and for glassy Cu68Zr32. From the last two parameters, one may calculate the shear and bulk stiffnesses of the glasses. For the Fe-B series the shear stiffness decreases by ∼13% when the B concentration decreases from 23 to 15 at.%; the bulk stiffness simultaneously decreases by ∼45%. As a result, the bulk stiffness of the near-eutectic alloy Fe85B15 (≃111 GPa) is strongly depressed relative to that for pure crystalline Fe (≃169 GPa) and that for crystalline Fe3B (≳163 GPa). The ratios of bulk stiffness to shear stiffness for Cu68Zr32 (≃4.7) and Fe40Ni38Mo4B18 (≃2.6) are relatively large and similar to those previously observed for other metallic glasses. For Fe85B15 the observed ratio is ≃1.9, which is quite close to that ( (5)/(3) ) expected for a solid bonded by centrally directed interatomic forces (a Cauchy solid). For the glasses examined here, as well as those examined previous, there is a linear proportionality between microhardness (H) and shear stiffness (μ); on average H≃μ/6.1.
Indentation rosettes and dislocation locking by oxygen in silicon
Authors: Harada Hirofumi , Sumino Koji
Published: February 2003

The characteristics of indentation behavior are investigated for float-zone silicon crystals and Czochralski silicon crystals over a wide range of temperature. It is shown that the deformation process to produce an indentation is not influenced by the oxygen content. The wing length of the dislocation rosette around the indentation which is subjected to high-temperature annealing is shorter in Czochralski crystals than in float-zone crystals. The results are interpreted satisfactorily in terms of locking of dislocations by oxygen atoms in the former type of silicon crystal during their rearrangement.
Shock induced transition stresses for zinc sulfide and zinc selenide
Authors: Gust W. H.
Published: February 2003

Three wave shock structures associated with the Hugoniot elastic limits and the solid-solid phase transitions have been measured for zinc sulfide and zinc selenide. The Hugoniot elastic limits were found to be 3.4±1 GPa for zinc sulfide and 3.0±1 GPa for zinc selenide. The phase transition stresses were 17.4±1.2 GPa for zinc sulfide and 14.6±1 GPa for zinc selenide. Both materials exhibited shear strength above the Hugoniot elastic limit.