bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared reflectivity spectra and Raman spectra of Ga1−xAlxAs mixed crystals
Authors: Kim O. K. , Spitzer W. G.
Published: February 2003

Thick layers of Ga1−xAlxAs with uniform composition were grown by an isothermal liquid-phase epitaxial technique. Infrared reflectivity and Raman-scattering spectra were measured with the same samples. The clean ’’two mode’’ behavior was confirmed in the reststrahlen band region, and the infrared reflectivity spectra were analyzed by using a Kramers-Kronig dispersion relation and by curve fitting to two forms for the classical dielectric function, one an additive form and the other a factorized form. The experimental data are in good agreement with the calculated TO and LO frequencies, when the Chang-Mitra model has been modified with the assumption of a nonlinear dependence of the oscillator strengths on composition. In the Raman spectra, the disorder-activated LA mode near 200 cm−1, a mode near 250 cm−1, and a background-level change were observed and attributed to atomic disorder. In the infrared reflectivity measurements the major disorder-induced effect was the increase in the TO and LO damping constants.
Amorphous-crystalline transition of arsenic-implanted silicon caused by multiple-pulsed ruby laser
Authors: Gibbons J. F. , Regolini J. L. , Lietoila A. , Sigmon T. W. , Magee T. J. , Peng J. , Hong J. D. , Katz W. , Evans C. A.
Published: February 2003

A free-running ruby laser has been used to anneal the damage produced when 3×1014 As/cm2 is implanted at 100 keV into Si initially at room temperature. At an on-target energy level of 15–30 J/cm2 and a pulse length of ∼1 ms it is found that 32 pulses are sufficient to recrystallize the implanted layer. It is found that localized (1–5 μm) islands recrystallize completely through the amorphous/crystalline layer allowing a certain areal portion of the latter to be recrystallized on the substrate for each pulse. This localized recrystallization appears to arise from melting in these regions caused by the nonuniform energy density of the laser beam. By operation of the laser in this mode the creation of damage (craters) often seen when using high-power Q-switched pulses can be avoided. TEM, SIMS, RBS, and electrical measurement are used to support these conclusions.
High-intensity laser photolysis of OCS at 157 nm: S(1S) production, photoionization, and loss
Authors: Rice James K. , Woodworth Joseph R.
Published: February 2003

We have observed the production of significant concentrations of electrons in high-intensity pulsed-laser photolysis of OCS to S(1S) at 157 nm. These results imply a photoionization cross section for S(1S) of 2.6×10−19 cm2. We have measured the quenching of S(1S) for a variety of conditions, including incident laser fluences of 100 mJ/cm2 and initial S(1S) densities of 3×1016 cm−3. Quenching by electrons can be minimized by adding diluents such as SF6 or CF4. We interpret our observed S(1S) decay rates in terms of quenching by S(3P) with a rate constant of 3×10−11 cm3 sec−1 and by CS [and/or O(3P)] with a rate constant near 2×10−10 cm3 sec−1. The measured S(1S) lifetime decreases with increasing initial S(1S) density, reaching a value of about 1 μsec at a S(1S) density of 3×1016 cm−3. The quantum yield for S(1S) production is found to be high (near 0.8) and independent of incident laser flux or added diluent pressure. These storage times and production efficiencies are consistent with the possible use of the S(1S) →S(1D) transition as an efficient high-energy-storage laser.
Electron-beam-induced diffusion during thin-film depth profiling
Authors: Röll Klaus , Losch Wolfgang , Achete Carlos
Published: February 2003

Diffusion induced by the electron bombardment during AES depth profiling is studied in multilayer thin films of Cu and Ni. The composition change depends both on the electron input power and on the actual film thickness since the heat dissipation by the metallic film is continuously reduced during sputtering. Theoretically, the temperature is estimated to rise up to 260 °C when an electron beam with an energy of 2 keV, electron current of 15 μA, and beam diameter of 80 μ is used.
Spectral-response and diffusion-length studies of amorphous, polycrystalline, ribbon, epitaxial, and single-crystal silicon MIS solar cells
Authors: Dey S. K. , Anderson W. A. , Delahoy A. E. , Cartier C.
Published: February 2003

Spectral-response and diffusion-length characteristics of the various MIS cells developed at Rutgers and previously reported in the literature have been investigated. The cells, designated according to the type of Si substrate used, appear in the following descending order based on the above studies: (1) Monsanto single-crystal Si with a peak quantum efficiency (QE) of 87.4% and a diffusion length (Ln) of 70 μm, (2) Wacker polycrystalline Si, peak QE=82.8%, Ln=60 μm, (3) IBM ribbon Si, (4) epitaxial Si, (5) Mobil-Tyco EFG ribbon Si, and (6) amorphous Si (Plasma Physics Corp.). Theoretical plots of quantum efficiency and short-circuit current density are shown to be in reasonable agreement with experimental results. The enhanced ultraviolet response of the MIS cell compared to that of a commercial N/P junction cell is demonstrated even though the latter device has a peak QE of almost 100% and an Ln value of 184 μm. The spectral studies lend support to the conclusions derived from the previously measured electrical parameters. The Wacker polycrystalline material is shown to be a strong contender in the race for terrestrial solar-cell applications. a-Si cells studied in this report exhibit a cutoff at λ=0.75 μm, indicating the influence of the energy gap. This cutoff corresponds to a band-gap energy of 1.65 eV which is in agreement with the published data for similar materials.
The reflectance of dendritic-tungsten surfaces
Authors: DiStefano T. H. , Pettit G. D. , Levi A. A.
Published: February 2003

The relatively low total optical reflectance measured from the surface of dendritic tungsten is quantitatively explained in terms of multiple reflections from the surface structure. A geometrical optical model is found to adequately describe the multiple reflections from dendrites which have an average spacing of about 5 μm. Coefficients representing the fraction of light reflected a given number of times are determined by analysis of the total reflectance of the dendritic surface on which an antireflective coating has been formed by anodization. At most wavelengths, second-order reflection (or light twice reflected) is found to dominate the reflectance of the dendritic surface for angles of incident light up to about 60° from normal, beyond which the first-order reflection becomes dominant. Based on the model, the reflectance of a geometrically characterized dendritic surface can be predicted for any type and thickness of antireflective coating.
Transient conduction phenomena in non-Ohmic zinc oxide ceramics
Authors: Eda Kazuo
Published: February 2003

Transient conduction phenomena in non-Ohmic ZnO ceramics are studied. Several characteristic phenomena are observed by applying a rectangular-wave-pulse voltage, such as the gradual increase of current, the voltage overshoot, the current overshoot, and the current oscillation. In order to clarify these phenomena, the experiments of the effect of additives, the temperature dependence, and the effect of preinjection of carriers have been carried out. These phenomena of gradual increase of current and voltage overshoot, current overshoot, and current oscillation can be reasonably explained by the electron trapping in the intergranular layer, by the delay in the formation of conduction electrons, and by the generation of the group of excess electrons in the intergranular layer, respectively.
PMMA fracture surface produced by ultrasonically modulated tensile stress
Authors: Takahashi K. , Nagai A. , Miyauchi Y. , Hyodo S.
Published: February 2003

Ultrasonic shear waves with a large amplitude and a frequency of 3.63 MHz were applied to a notched PMMA plate under uniaxial tension in order to produce artificial Wallner lines by altering the direction of the maximum principal stress during the rapid growth of fracture. The amplitude of the lines generated was found to be of the order of 10–102 nm and has been shown to change proportionally to the input-wave amplitude. The interference colors observed indicate that the PMMA crack front is very liable to proceed inside the crazed layer ahead of the front; despite the intensive ultrasonic stress modulation very few cracks which reached or crossed the craze-matrix boundaries were found.
Theoretical analysis of constricted electric arc by iteration method
Authors: Mehta R. C.
Published: February 2003

An analytical solution of the energy equation for the constricted electric arc of argon plasma is obtained by the Laplace transform. An iterative scheme is employed to accommodate variable transport properties. It has been concluded that the effect of the variable properties is to increase axial electric field intensity and wall heat flux. It is also observed that the limiting value of a nondimensional parameter containing Ohmic heating and specific radiated power is 5.76. Results for voltage-current characteristics, using the present analysis, are found to be in good agreement with the experimental data of Maecker.
Lattice deformation and misorientation of InxGa1−xAs epitaxial layers grown on InP substrates by molecular-beam epitaxy
Authors: Kawamura Yuichi , Okamoto Hiroshi
Published: February 2003

Lattice deformation and misorientation of InxGa1−xAs epitaxial layers grown on InP substrates by molecular-beam epitaxy is measured from rocking curves of an x-ray double-crystal monochrometer. It is concluded that the epitaxial layers are deformed from cubic to tetragonal and misoriented to the substrates except in lattice-matched epilayers. This result suggests that the substrate lattice has a large influence on the structure of the epitaxial layers.
Possibility of mobility fluctuations in the flicker noise of nondegenerate semiconductors
Authors: Min Hong S.
Published: February 2003

A condition for fluctuations in the mobility of the free charge carriers in nondegenerate semiconductors is derived. It is shown that to have mobility fluctuations quasiequilibrium should not hold.
Composition and refractive index of Ga1−xAlxAs determined by ellipsometry
Authors: Kuphal E. , Dinges H. W.
Published: February 2003

The compositions of 42 thin Ga1−xAlxAs layers grown by liquid-phase epitaxy were measured by reflection ellipsometry. The refractive index n (x) was determined over the composition range x?0.61 at the wavelength λ=546.1 nm. The composition of the calibration samples was obtained from electron microprobe analysis. The 800 °C solidus isotherm of the Ga-Al-As phase diagram is determined and compared with existing phase diagrams. Furthermore, the thickness of the natural oxide layers on the samples was measured as a function of alloy composition and of time.
Determination of the electrical properties of semi-insulating GaAs: A role of the magnetic field dependences of single-carrier parameters
Authors: Betko J. , Měřínský K.
Published: February 2003

The electrical properties of four semi-insulating GaAs : Cr crystals in the temperature range 295–430 K have been determined by using the mixed conductivity analysis, taking into account the magnetic field dependences of single-carrier conductivities and Hall coefficients. It is shown that when the field dependence of the electron single-carrier Hall coefficient is neglected, a very large error in the determination of the hole mobility and carrer concentrations may arise. The intrinsic concentration at various temperatures is calculated from the experimental data and its value at 296 K is ni≈ (2.4±0.3) ×106 cm−3, which compares within a factor of about 1.6 with theoretical values deduced from the band gap and effective masses. The temperature dependences of electron and hole Hall mobilities are found to be rnμn∼T−(0.5–1) and rpμp∼T−2.5, respectively. The determined electron-to-hole concentration ratios for individual samples are in the range 0.01–0.3 which corresponds to the Fermi level lying within ±0.03 eV from the middle of the band gap.
Interface states in a cleaved metal-silicon junction
Authors: Barret C. , Vapaille A.
Published: February 2003

By studying the capacitance of a forward-biased Schottky diode it is possible to determine the energy distribution and relaxation time of interface states. This method is applied to contacts between chromium and silicon cleaved in ultrahigh vacuum. The presence in the silicon gap of interface states in equilibrium with the semiconductor and distributed in a set of energy bands is established. The characteristics of each band (energy position, density, and capture cross section) are identified. The origin of these states is discussed, and it is argued that they are characteristic of the silicon surface.
On estimating remanent magnetization from x-ray pole figure data
Authors: Herbst J. F. , Tracy J. C.
Published: February 2003

The appropriate procedure for estimating the ratio of remanent-to-saturation magnetization from x-ray pole figure data on uniaxial ferromagnets is described. An oversight existing in the literature regarding this problem is corrected, and it is demonstrated that x-ray crystallographic information can be quantitatively related to magnetic properties. A figure of merit for alignment is also proposed.
High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film
Authors: Chen Tu , Charlan G. B.
Published: February 2003

The coercivity, hysteresis loop squareness, and microstructure of the sputtered Co and Co-rich Co-Re alloy thin films are presented. Correlations between the microstructures and the magnetic properties are established. It was found that the sputtered Co films have a mixture of fcc and hcp phases, making it impossible to obtain sputtered Co films possessing both high Hc and high M-H loop squareness. For Co-Re alloy films however, it was possible to obtain films with a pure hcp phase below substrate temperatures of 300 °C. By controlling the microstructure of the Co-Re films through variation of the sputtering variables, films having Hc’s up to 700 Oe and squareness ratios (Mr/Ms and S*) of more than 80% were obtained. The micromagnetic structures of these Co-Re films were also investigated using Lorentz microscopy and the results are discussed in terms of the microstructure and magnetocrystalline anisotropy of the film.
Two-dimensional modeling of aerosol-induced breakdown in air
Authors: Edwards A. L. , Fleck J. A.
Published: February 2003

The dynamics of aerosol-induced breakdown in air is described using a three-temperature nonequilibrium thermodynamic model of the air plasma and two-dimensional Lagrangian hydrodynamics. From a heated sphere of air used as the initial condition an expanding laser-supported absorption wave develops, provided a maintenance intensity-threshold criterion is met. The maintenance threshold is close to 6×106 W/cm2 for 10.6-μm radiation. Although the absorption wave develops a shock, it differs in important ways from a one-dimensional laser-supported detonation wave due to its two-dimensional character.
Effect of surface capacitance on the dielectric behavior of ferroelectric lead germanate
Authors: Mansingh Abhai , Srivastava K. N. , Singh Bachchan
Published: February 2003

The results of dc conductivity and the thickness dependence of the dielectric constant at 1, 10, and 100 kHz of ferroelectric lead germanate (Pb5Ge3O11) are reported for two electrode materials. The activation energy (dc) has been found to be 0.91 and 0.62 eV in paraelectric and ferroelectric phases, respectively. The dielectric constant decreases with decreasing thickness of the samples at all frequencies and the dielectric constant for evaporated gold is found to be higher than that for the silver-paint electrode. These results have been explained by assuming the formation of a homogeneous surface layer due to the potential barrier at the metal insulator junction. The surface capacitance shows a frequency dependence which may be due to the relaxation time associated with the surface layer. A possible mechanism for the formation of the surface layer is also discussed.
Liquid crystal quasihomeotropic orientation induced by a polymer deposited on a SiO surface
Authors: Rousille L. , Robert J.
Published: February 2003

A new method is described that induces a slight tilt angle for the molecules of a homeotropically aligned liquid crystal. A thin plasma polymerized film is deposited after an oblique SiO layer on the electrodes of the LC cell, to give the ’’quasihomeotropic’’ structure. Such cells do not show any disclination lines and have a good electro-optical behavior.
Inert-gas-bubble formation in the implanted metal/Si system
Authors: Tsaur B. Y. , Liau Z. L. , Mayer J. W. , Sheng T. T.
Published: February 2003

Inert-gas-bubble formation has been observed as a result of ion bombardment of thin metal films (Cr, V, Ni, Ti, or Pd) deposited on Si substrates. Rutherford backscattering measurements and cross-sectional transmission electron microscopic analyses indicated that the gas bubbles were formed predominantly near the interface between the Si substrate and the surface layer. In addition, pronounced mixing between Si and metal was observed. Both bubble formation and Si-metal intermixing are interpreted in terms of ion-induced atomic migration within the collision cascade around the ion track. With increasing ion dose, the number of gas atoms trapped in the bubbles at the interface continued to grow and the surface layer peeled off at high doses.
Electron drag on mobile dislocations in niobium
Authors: Tregilgas J. H. , Galligan J. M.
Published: February 2003

The interaction of mobile dislocations with electrons in niobium, through its temperature dependence and its field dependence, are described. It is found that the difference in stress between the normal state and the superconducting state varies in a linear manner with temperature between Tc and 0.2Tc, while the difference in stress between the mixed state and the superconducting state is nonlinear with field at constant temperature. These results are compared with various models of dislocation motion in metals.
Dynamic model for e-beam irradiation of MOS capacitors
Authors: Churchill J. N. , Holmstrom F. E. , Collins T. W.
Published: February 2003

The dynamic properties of a metal-oxide-semiconductor (MOS) capacitor during e-beam irradiation was simulated using numerical techniques. Poisson’s equation and the trap dynamics were used to calculate the time-dependent behavior of electrons, holes, and traps in the oxide during and after irradiation for various typical conditions. These results were used to calculate flatband shift versus gate bias voltage for steady-state as well as non-steady-state conditions. These exact computations confirm a previously published approximate two-layer model for irradiated MOS capacitors.
Time-resolved dark injection from various metals into an amorphous semiconductor
Authors: Abkowitz M.
Published: February 2003

The evolution from transient conditions to dark-current steady state following the application of a step field to a-As2Se3 sandwich cells fitted with Bi, Ni, Ag, Au, Sn, C, Ga, Al, and Cu has been measured. J-vs-E characteristics are in almost all cases found to be similar to those already published on the Au : a-As2Se3 system. These J-vs-E characteristics show both an extensive region of linear field dependence and a superlinear region in which the current is not space-charge limited. Dark currents in a-As2Se3 and related chalcogenides have been described in terms of a single bulk-controlled mechanism operative at all fields, meaning that contact invisibility (Ohmicity) has been tacitly assumed. At fields exceeding 104 V/cm, the hole transit time in a-As2Se3 becomes the dielectric relaxation time and under these circumstances an Ohmic contact will, under step-field excitation, exhibit a well-characterized space-charge-limited transient response. None of these contacts exhibit this response; instead they behave as finite injectors supplying holes with a diminishing efficiency in the time after application of a voltage step and at a rate which is always much less than CV per transit time. The resulting small-signal transient response exhibits a local maximum at a time following excitation which is significantly affected by the contact-reservoir decay time. The steady-state dark-current density above 104 V/cm must therefore reflect an injection efficiency relatively insensitive to the choice of contact.
Direct evidence for the nonassignment to oxygen of the main electron trap in GaAs
Authors: Huber A. M. , Linh N. T. , Valladon M. , Debrun J. L. , Martin G. M. , Mitonneau A. , Mircea A.
Published: February 2003

From the direct comparison between quantitative atomic oxygen concentration and electronic deep-energy-level concentration in GaAs, it is concluded that oxygen is not involved, either directly or as part of a complex defect, in the origin of the main electron trap at EC−0.75 eV.
Long-wave approximations for the scattering of elastic waves from flaws with applications to ellipsoidal voids and inclusions
Authors: Gubernatis J. E.
Published: February 2003

We discuss three long-wave approximations (the Born, quasistatic, and extended quasistatic) to the scattering of elastic waves from a flaw embedded in an isotropic medium. First, we derive the Born and quasistatic approximations by the technique of infinite-order perturbation theory. For these approximations this derivation clearly reveals the precise nature of the approximations and the generality of the quasistatic approximation in particular. Next, we give the complete details on how to calculate within the three approximations the long-wave scattering from ellipsoidal voids and inclusions. Then, we calibrate the approximations by comparison with exact results for the scattering from a sphere and also present computations based on the extended quasistatic approximation for the scattering from various ellipsoidal voids.
Scattering of elastic waves by circular cylindrical flaws and inclusions
Authors: Jain D. L. , Kanwal R. P.
Published: February 2003

The problems of scattering of plane compressional and shear waves by a class of infinite circular cylindrical flaws and inclusions embedded in an infinite isotropic homogeneous elastic medium are solved. The objects considered are an elastic cylinder, an inviscid-fluid-filled cavity, an empty cavity, and a rigid cylinder. Approximate formulas are derived for the displacement fields, stress tensors, far-field amplitudes, dynamic stress intensity factors, and the scattering cross sections. It is assumed that the wavelength is large compared to the radius of the scatterer. Various elastostatic limits are also presented. Some of these results even in elastostatics appear to be new.
An investigation of the effects of system parameters on the production of hollow hydrogen droplets
Authors: Guttman J. L. , Hendricks C. D. , Kim K. , Turnbull R. J.
Published: February 2003

Many inertial confinement target designs have the fuel as a frozen spherical shell of hydrogen isotopes. One method of manufacturing these targets would be to produce the spherical shell first. In this paper we report on an experimental study on the production of spherical shells of liquid and solid hydrogen. These shells are made by acoustically breaking up a jet of superheated liquid hydrogen into drops and at the same time cavitating a bubble in the center of each drop. The resulting growth of the bubbles by evaporation produces the spherical shells. The size and the aspect ratio of the spherical shells are found to be affected by several parameters. The mass of the drop depends on the diameter of the nozzle from which the jet emerges. Also, varying the frequency of the acoustic excitation gives some control of the droplet size. The aspect ratio depends most strongly on the liquid temperature and the droplet-chamber pressure. Increasing the temperature or lowering the pressure increases the aspect ratio of the shell. If the pressure is lowered below the triplet-point pressure of hydrogen, the shells freeze forming a spherical shell of solid hydrogen.
Energy band of ternary alloy semiconductors—Calculation by a coherent-potential approximation based on the method of linear combination of bond orbitals
Authors: Sakai Shigeki , Sugano Takuo
Published: February 2003

A method of calculating the effect of the random distribution of atoms on the energy-band structure of ternary alloy semiconductors is proposed, where the coherent-potential approximation based on the method of linear combination of bond orbitals (LCBO) is used. In the case of GaAscP1−c, the nonlinear dependence of the energy upon the alloy composition c at various symmetry points within the first Brillouin zone is calculated. It is found that the effect of disorder is an important factor in explaining the bowing effect of band gaps; In particular, the magnitudes of the direct gap Γv15→Γc1, and the indirect gap Γv15→Xc1 agree well with experimental results. The energy-band structure, including the lifetime broadening of the energy at each Bloch state, is shown for GaAs0.5P0.5. Also, the relation between the LCBO parameters and the effect of disorder on various states is qualitatively discussed. The effect of disorder on the p-like or s-like states of the valence band increases with increasing the difference between the p-like or s-like energy levels, which are represented by the bonding orbitals, of both alloy constituents. The relation between the effect of disorder on the conduction band and the antibonding orbitals is the same as the relation between the effect of disorder at the sites of group-V atoms and that at the sites of group-III atoms appears noticeably at the points Xc1 and Xc3 of the conduction band and at the points Xv1 and Xv3 of the valence band.
Transport of spatially inhomogeneous current in a compensated metal under magnetic fields. I. Potential and current distributions
Authors: Yoshida Katsukuni
Published: February 2003

A theoretical investigation of a spatially inhomogeneous distribution of electric current in a compensated metal under external magnetic fields has been made in terms of a boundary-value problem. The current inhomogeneity considered is what is yielded from a point electrode. The calculated results demonstrate the following. Application of high magnetic fields causes marked changes in both the potential and current distributions. In an oblique magnetic field, a potential mountain or valley is newly formed on a boundary surface. Responsively, the current is highly condensed around a line parallel to the magnetic field. Such condensation of the current induces space charges around this line.
Transport of spatially inhomogeneous current in a compensated metal under magnetic fields. II. Dynamical properties of the current system
Authors: Yoshida Katsukuni
Published: February 2003

Dynamical behavior of an inhomogeneous current system under the control of external magnetic fields has been theoretically and experimentally investigated for a medium consisting of a compensated metal. Application of an oblique magnetic field H results in the appearance of a potential mountain or valley on a surface of the medium and also in the condensation of current around a line parallel to H. When the direction of H is continuously varied, the top of the mountain (or the bottom of the valley) scans the relevant surface. This scanning brings about a dip and hump pair on an angular dependence curve of potential difference between probes. The top of the mountain can move also when the strength of H is varied. The current system is found to be sensitive also to the specimen thickness and to the placement of electrode. Some experimental results for a bismuth specimen are demonstrated.
Microfabrication and evaluation of diffractive optical filters prepared by reactive sputter etching
Authors: Knop K. , Lehmann H. W. , Widmer R.
Published: February 2003

Single or linearly superimposed square-wave surface-relief patterns in a transparent plate yield optical transmission characteristics similar to those of interference filters. Reactive sputter etching of fused quartz in CHF3 using Shipley 1350 H photoresist as an etch mask offers a well-controlled method to produce these complex structures. Gratings with periodicities of 1–2 μm and depths of up to 3 μm are fabricated with dimensional tolerances of ±0.02 μm using laser interferometric techniques. Superposition is obtained by successive masking and etching operations. The optical transmission characteristics of these diffractive filters are analyzed and compared with rigorous diffraction theory.
Metastable decay rates in a Cu-metal-vapor laser
Authors: Miller J. L. , Kan T.
Published: February 2003

The decay of the density of the metastable Cu (4s2 2D5/2) state following a discharge pulse in a copper-metal-vapor laser was measured with a 510.6-nm cw dye-laser probe. Investigation of the Cu and He density dependence of the decay time constant indicated that particle diffusion was the dominant loss mechanism.
Refractive-index profile and resonant modes in GaAs lasers
Authors: Nunes F. D. , Patel N. B. , Mendoza Alvarez J. G. , Ripper J. E.
Published: February 2003

We examine the form of the refractive-index profile that has to exist in the direction parallel to the junction in a semiconductor junction laser in order to explain the experimentally observed spectral separation between adjacent transverse modes parallel to the junction. We show that previously assumed profiles are unsatisfactory. We present a form of profile that results in predicting mode wavelength separation that is in agreement with experimental data.
Theoretical study of magnetic pick-up transducers for gravitational wave antennas
Authors: Papini G. , Strayer D. , Tward E. , Lim C. S.
Published: February 2003

Magnetic pick-up transducers for high-Q gravitational wave antennas are studied. The sensitivities of two recently proposed devices are evaluated from a general point of view. A general treatment of these systems as two coupled oscillators is used. The noise properties of these devices, taking into account the reaction of the electronics back on the antennas and the measuring times, are determined. A modification of the systems to operate as mechanical impedance transformers is also discussed. A comparison of two recently proposed magnetic transducer schemes with a mechanical impedance transformer scheme is made.
An analysis of the wave impedance and the attenuation constants of a concentric line having a helical inner conductor
Authors: Chiba Jiro , Sato Risaburo , Nimura Tadamoto
Published: February 2003

In this paper we describe an analysis of the wave impedance and the attenuation constant of a shielded wire helix. Analyses are made by the wire theory. Helix analyses are chiefly done by the sheath theory and the tape theory, but these make models, that are infinitely thin ideal cylinders and infinitely thin tapes, so in the case where a helix wound with finite sectional area wires is used with shielding, conditions vary and it is insufficient for contributing to a design at the time when winding encounters difficulties: it is difficult to estimate the effect of the diameter of the wire on the attenuation constant α and wave impedance Z0. So the case in which the wire helix had a shielding cylinder was analyzed in this paper. The numerical results are also presented as graphs.
Energy extraction from a large-volume HF laser amplifier
Authors: Hoffman J. M. , Patterson E. L. , Gerber R. A.
Published: February 2003

Energy extraction from a large-volume HF laser amplifier has been measured as a function of input intensity. Both the oscillator and amplifier were operated with similar gas mixtures of H2 and F2, which assured a good spectral match between the oscillator and amplifier. The amplifier input intensity was varied from 104 to 2×107 W/cm2. An input intensity of 2×107 W/cm2 extracted an energy equal to about 90% of the energy extracted from the amplifier when it was operated as an oscillator. The experiment also demonstrated that an input intensity of 104 W/cm2 decreased the amplified spontaneous emission intensity by a factor of 2 from the value with no input. Increasing the input intensity level above 104 W/cm2 did not further reduce the amplified spontaneous emission.
Spatial- and temporal-intensity distribution of stimulated Raman emission
Authors: Lowdermilk W. H. , Kachen G. I.
Published: February 2003

Spatial- and temporal-intensity distributions of stimulated Raman scattering are found to be severely modulated compared with the incident laser beam. Solutions of Maxwell’s equations show the modulation results from nonlinear amplification of small-amplitude fluctuations in the collimated laser-beam intensity. The modulation growth is limited by diffraction and laser saturation.
The high-pressure neutral infrared xenon laser
Authors: Lawton S. A. , Richards J. B. , Newman L. A. , Specht L. , DeTemple T. A.
Published: February 2003

The near infrared laser emission from Xe in Ar and He mixtures has been investigated experimentally in an ionizer-sustainer mode, and theoretically. An efficiency of 1.3% has been achieved from Ar : Xe, 150 : 1, at 1900 Torr with aproximately 75% of the output contained in a single line at 1.73 μm. Based on a detailed kinetic study of the discharge, the laser behavior is attributed to a two-stage excitation in which a large excited-state population is created during the first portion of the discharge followed by excitation and ionization of these excited states and strong lasing during the remaining low-field portion. The processes leading to the strong emission include electron-impact excitation from low-lying excited states, dissociative recombination pumping, and cascade pumping from higher-lying levels, all of which means that the original excitation energy is being recirculated. The desired high Ar pressure is explained on the basis of providing an impedance match to the sustainer circuit and because the elastic (momentum) losses, at low fields, are nominal allowing a small excited-state density to dominate the fractional-loss spectra.
Acousto-optic properties of tellurium at 10.6 μm
Authors: Fukuda S. , Shiosaki T. , Kawabata A.
Published: February 2003

Experimental results are described for the acousto-optic properties of Te at the 10.6-μm wavelength of CO2 laser light. It is found that Te possesses exceptionally large figures of merit. The largest value of M, 5850×10−18 sec3/g, is obtained for a longitudinal acoustic wave propagating in the x direction and incident light polarized along the z axis. Five of the eight independent photoelastic tensor components are calculated from the measured figures of merit and the effects of optical activity on these results are discussed. The practical applicability of Te as an acousto-optic medium is evaluated.
On the equivalence between Boussinesq and Timpe approaches to the torsion-free axisymmetric problems of elasticity
Authors: Tran-Cong T. , Steven G. P.
Published: February 2003

Several different solutions have been presented for the Lamé equation of elastic equilibrium. This paper examines, via an intermediate solution, the equivalence between two classical forms of solution, namely, those of Boussinesq and Timpe. By the use of this equivalence it is possible to transform the displacement fields arising from each solution from one to the other.
High-intensity laser-matter coupling in a vacuum
Authors: Nielsen P. E.
Published: February 2003

A simple analytic model is developed for the steady-state ablation of a surface irradiated by an intense laser in a vacuum. The model accounts for the absorption of laser light in the plasma plume over the surface, as well as the reradiation of a specified fraction of the energy absorbed to the surface, where it augments the ablation rate. We find qualitative differences in the scaling of thermal and mechanical coupling to the surface with laser intensity depending on whether or not the coupling from the plasma is significant, and compare these predicted scalings with experimental data for evidence of plasma-enhanced coupling in vacuum. We conclude that in many cases there is no such enhanced coupling and provide simple physical arguments for why this is so.
The drag force on a moving dislocation, I. Zero temperature (lattice drag force)
Authors: Partom Y.
Published: February 2003

The kinematics and equations of motion of an equivalent single-degree-of-freedom system for a moving dislocation in a modified Frenkel-Kontorova linear-chain model are derived and then used in conjunction with computer simulation runs. The average drag force on a moving dislocation at zero temperature (lattice drag force) is computed for a range of dislocation velocities. At a velocity comparable with the loss-free velocity, obtained by Earmme and Weiner from a steady-state solution, we obtain a minimum value for the lattice drag force. For velocities above the loss-free velocity the results agree with those obtained fom steady-state solutions by Earmme and Weiner. Below the loss-free velocity the lattice drag force is relatively small. It goes through a maximum which is of the order of 10−4 times the interatomic spring constant k1 of the model.
Amplitude dependence of dislocation damping in high-purity copper after quenching and during 1-MeV electron irradiation
Authors: Kerans R. J. , Simpson H. M.
Published: February 2003

Dislocation damping as a function of strain amplitude following quenching and during 1-MeV electron irradiation was investigated by measuring Young’s modulus and the logarithmic decrement in high-purity polycrystalline copper. A ’’peaking effect,’’ an initial increase and subsequent decrease in the damping, was observed at all strain amplitudes during electron irradiation. A somewhat subdued peaking effect was observed only at high strain amplitudes following quenching.
Optical absorption of lithium nitride
Authors: Brendecke H. , Bludau W.
Published: February 2003

The optical absorption of Li3N single crystals has been measured in the energy range 1–7 eV at various temperatures between 4.2 and 300 K in the two polarizations E∥c and E⊥c for the two crystal orientations k∥c and k⊥c. Strongly anisotropic behavior of the optical absorption edge is reported. The energy gap in the E∥c polarization is indirect with EG=2.15 eV at 4.2 K and EG=2.00 eV at 300 K. Two peaks in the absorption edge E⊥c are ascribed to the creation of excitons, which are bound to directionally arranged defect complexes.
Dislocation motion and generation in LiF single crystals subjected to plate impact
Authors: Kumar P. , Clifton R. J.
Published: February 2003

A plate-impact technique is developed for subjecting low-dislocation-density single crystals to a submicrosecond square pulse under conditions which allow recovery of the crystal for examination of changes in dislocation configurations. Subsequent reflected waves in the crystal are minimized by use of a longitudinal-momentum trap and a specially designed flyer plate shape. Transmitted wave profiles are monitored with a laser displacement interferometer. Dislocations are observed by means of etch pits. Experiments carried out on both annealed and irradiated single crystals of high-purity LiF show newly generated dislocations occurring primarily in the form of glide bands. Average dislocation velocities computed from the lengths of interior glide bands are, for the annealed crystals, proportional to the resolved shear stress. The proportionality constant corresponds to a drag coefficient B?3×10−4 dyn sec/cm2, which agrees reasonably well with values determined previously at much lower (one to four orders of magnitude) stress levels. Thus, it appears that, in annealed high-purity LiF at room temperature, the intrinsic resistance of the lattice to the motion of dislocations is characterized adequately by a linear viscous drag for dislocation velocities in the range from near zero to at least one-fourth the elastic shear-wave speed.
Estimation of surface-acoustic-wave attenuation due to platelet defects
Authors: Kimura Takashi , Kotaka Isamu , Yoshikawa Shokichiro
Published: February 2003

Surface-acoustic-wave (SAW) attenuation due to platelet defects in quartz substrate (40° rotated Y cut) was investigated. The dimensions of the defects, which are formed in a lapping and polishing process, were quantitatively measured. The data was used in the analytical calculation. SAW attenuation loss in propagating on damaged substrate with deep defects was experimentally measured in the 150–400-MHz frequency range. The loss was obtained from the measured Q value of an IDT resonator, comprising the substrate. By comparing the Q value of the resonator using damaged substrate with that using undamaged substrate, the loss caused by the defects was discriminated from other losses. Steg’s scattering theory was applied to the SAW device and the calculated attenuation loss agreed well with the measured one. The theory also predicts that the attenuation constant in conventionally polished substrate, which contains about 2×104 cracks/cm2 microcracks, is about 1 dB/cm at 1 GHz.
High-pressure Hugoniots of porous silicates
Authors: Kincheloe N. K. , Rehfuss D. E. , Anselmo J. C.
Published: February 2003

Porous Hugoniots as formuated by Hermann’s constitutive approach are expected to be accurate at shock pressures only below 1 Mbar because his equation of state does not include elastic and electronic contributions to the total pressure and because he assumes a density variation of the Grüneisen parameter which is suitable only at low pressures. In contrast, the method presented here is valid only above about 1 Mbar. We first interpret porous aluminum data in a new way, finding shock pressure U analytically related to particle velocity u through the distention parameter m, where m=V00/V0 and V0 is standard unshocked specific volume. That is, we develop an equation U=U (u,m) which fits available shock data with excellent statistical correlation coefficients. In the U (u) plane each distinct value of m defines a straight line which is one of a family of aluminum lines. Turning to quartz data, we hypothesize that, as far as high-pressure shocks are concerned either macroscopically porous sandstone or structural polymorphs of quartz may be considered as porous forms of stishovite; stishovite is assigned a distension of unity. In accord with that hypothesis, we find the family of quartz curves derivable from the family of aluminum curves by a rotational variation in the U (u) plane. On the basis of that successful rotational correlation between the aluminum and quartz families, we predict high-pressure (above 1 Mbar) porous Hugoniots of diabase, an astrogeologically interesting material which is compositionally about one-half quartz and is in density comparable to aluminum.
The evaluation of the input admittance of SAW interdigital transducers
Authors: Hussein A. M. , Ristic V. M.
Published: February 2003

Using the moment-method technique, the exact charge distribution on a finite interdigital array is obtained. Full account is taken of the coupling to bulk and surface modes. The moment-method technique greatly simplifies the evaluation of the transducer input admittance. The frequency dependence of the input admittance is computed for a different number of electrode pairs, different metallization ratio, and different sequences. The electrostatic capacitance is proved to be 28% higher than the zero-coupling capacitance for Y-Z lithium niobate.
Photocapacitance detection of deep centers in O-implanted zinc telluride
Authors: Katircioglu B. , Pautrat J. L.
Published: February 2003

The double-beam photocapacitance technique is used for the detection of deep centers in oxygen-implanted ZnTe. The photocapacitance spectra are compared with photoconductivity and photoluminescence data. It is shown that the classical interpretation of the trapping by transitions between a band and a localized level fails in this case since the absorption of light creates trapped excitons, which are thermally dissociated into a free hole and a bound electron. The electron-emission threshold gives the binding energy of the electron and thus allows the verification of the model of Hopfield, Thomas, and Lynch of the trapping of excitons to isoelectronic impurities. This verification can be done in the case of OTe-bound excitons. In order to get a precise value of the threshold energy a theoretical shape of the optical cross section is needed. It is shown that the classical Lucovsky formula, although giving a satisfactory fit, may be inadequate if the center is strongly coupled to the lattice. It is suggested that the experimental optical cross section is the convolution of a ’’no-phonon shape’’ with a Poisson distribution of phonon replicas. With this procedure the electron binding energy to OTe is found to be 0.4 eV, in agreement with the other determinations. The binding energy of the electron is also obtained for some of the other centers involving oxygen obtained after oxygen implantation in ZnTe.
Ion-beam diagnostics by means of an electron-saturated plane Langmuir probe
Authors: Weber Wim. J. , Armstrong Richard J. , Trulsen Jan
Published: February 2003

A new sensitive method for the detection of low-energy ion beams in low-pressure nearly collisionless unmagnetized plasma is presented. The method makes use of a swept planar Langmuir probe in the electron saturation regime. An ion beam with direction perpendicular to the plane of the probe produces a double knee (’’beam edge’’) on the characteristic at a positive bias with respect to plasma potential. The magnitude of this bias is a measure of the directed energy of the beam. It seems to be possible to deduce the beam temperature from the form of the beam edge. The amplitude of the beam edge is proportional to the beam ion flux. The size of the effect is much greater than can be inferred from ion collection alone. An explanation is suggested based on the presence of a space-charge layer in front of the probe produced by the reflected beam and that this layer in turn causes enhanced electron collection by the probe.
rf-SQUID magnetometer biased by harmonic
Authors: Yamashita Tsutomu , Onodera Yutaka
Published: February 2003

This paper describes a refined rf-SQUID magnetometer in which not only the fabrication of the SQUID sensor becomes easier but also the magnetic flux could be stably measured with sufficient sensitivity at a wider range of temperatures compared with existing SQUID systems. Two frequency components are used in the proposed rf-SQUID magnetometer, one of which is to excite the SQUID sensor and the other is to detect its response. Furthermore, from both the phenomenological analysis and the experimental results it is shown that the present rf-SQUID magnetometer performs its function well even if the value of LIc of the SQUID sensor is much larger than the flux quantum φ0.
Sensitivity of cw and pulsed laser-pumped Pr infrared quantum counters
Authors: Case W. E. , Chivian Jay S. , Reynolds R. W.
Published: February 2003

The characteristics of LaBr3 : Pr and LaCl3 : Pr infrared quantum counters used for detection near 4.5 μm have been investigated in detail. Quantum efficiency for infrared-to-visible upconversion is in agreement with our estimates based on the spectroscopic properties of these materials. Highest sensitivity was obtained with pulse laser pumping in LaCl3 : Pr at 82 °K. Maximum crystal quantum efficiency and detectivity under these conditions were Q=1.2×10−3 and D*=1.4×109 cm Hz1/2/W. The detectivity is the highest reported for any IRQC device. Pump-induced fluorescence measured without ir signal proved to be the limiting source of noise for both cw and pulsed pumping.