bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction of MgO in MgAl2O4 spinel with molybdenum crucibles during crystal growth
Authors: Schmid F. , Viechnicki D. , Kantor P. I.
Published: February 2004

Evidence is presented defining the reaction of free MgO in MgAl2O4 spinel powder with molybdenum crucibles under reducing conditions prior to crystal growth using the gradient furnace technique. This reaction results in strongly colored crystals but can be eliminated by sufficient heat treatment of the spinel powder to incorporate all the MgO into the spinel structure before melting.
Redetermination of elastic constants of single-crystals CaMoO4
Authors: Chung David Y. , Hoyte Alfred F. , Li Yuan
Published: February 2004

Values of the elastic constant of CaMoO4 obtained by Alton and Barlow are compared with those obtained using equations developed by Chung and Li. The velocities measured by Alton and Barlow were used in the computations.
On the interaction of prismatic and glissile dislocations
Authors: Narayan J.
Published: February 2004

A transmission electron microscopy study of the interaction between a prismatic dislocation loop and a straight dislocation moving in its glide plane in MgO is reported. The interactions are discussed in terms of Kroupa's theoretical estimates of interaction parameters.
Precipitation and solid solution effects in aluminum-copper thin films and their influence on electromigration
Authors: Walker G. A. , Goldsmith C. C.
Published: February 2004

With the recent discovery that the addition of copper to thin aluminum films increases the lifetime to electrical failure of the films, a large effort has been made to understand the role of the copper in the process. The present paper describes experiments on various types of thin polycrystalline films designed to understand the solid solution and precipitation effects in the films. It is shown that precipitation is different from the bulk and in turn different from thin-film work on unsupported single-crystal films. Possible mechanisms relating copper additions to electromigration lifetime are considered and the effect of total copper distribution in the films is found to be important. Differences in residual gas pressure in the vacuum system can alter precipitation processes.
Thickness dependence of conversion efficiency of ZnS film transducers for elastic surface waves
Authors: Inaba Ritsuo , Kajimura Koji , Mikoshiba Nobuo
Published: February 2004

The conversion efficiency of ZnS transducers evaporated on a glass substrate for elastic surface waves has been measured as a function of the ZnS film thickness and analyzed by using a simple model. It is found that the thickness dependence of the conversion efficiency is affected by elliptic particle motion at the position of electrodes located at the interface between the ZnS film and the substrate (type I) or at the surface of the ZnS film (type II). Conversion efficiency calculated from the potential induced at the electrodes is in good agreement with the experiments. The analysis shows that the internal impedance of the thin-film transducer is not simply proportional to Δ vs/vs, where Δ vs is the perturbation in surface-wave velocity when the electrodes are replaced by a thin-film perfect conductor. Theory suggests that type I is most efficient when the thickness is about 0.4 times the surface wavelength.
Blistering in helium-ion-implanted (111) niobium monocrystals
Authors: Das S. K. , Kaminsky M.
Published: February 2004

The formation of helium blisters on the (111) surface planes of monocrystalline niobium by implantation of 0.5–1.5-MeV helium ions has been investigated for total doses ranging from 0.1 to 1.0 C/cm2 for different target temperatures, angles of incidence of the projectiles, and channeling conditions. The results indicate that the blister shape is strongly dependent on target temperature. At 900 °C and for channeled projectiles, almost all the blisters have a threefold symmetry resembling a ``crow-foot'' shape. The alignment of the crow-foot blisters with respect to each other exhibits an asymmetry in that their prongs are aligned along only one set of 〈112〉 directions of the host niobium lattice such as [12̄1], and [112̄], and [2̄11] directions and not along the other equivalent set such as the [1̄21], [1̄1̄2], and [21̄1̄] directions. As the target temperature is lowered, the tendency to form dome-shaped blisters increases; at room temperature only dome-shaped blisters form. The average blister size appears to increase with decreasing target temperature, with increasing degree of channeling, and with increasing projectile energy; at room temperature the last of these variables is the one with the most pronounced effect on the size. The blister density is more than two orders of magnitude less for channeled projectiles than for unchanneled ones for irradiation at a target temperature of 900 °C. For the unchanneled projectiles, the angle of incidence of the projectiles does not appear to change the morphology of the blisters significantly.
Role of firing atmosphere on the rate of transformation of ZnS crystal
Authors: Sakaguchi M. , Hirabayashi T.
Published: February 2004

In order to investigate the role of firing atmosphere on the rate of transformation of a ZnS crystal, crystalline ZnS of hexagonal or cubic form was fired for 0.5–24 h at 800 and 1050 °C in each atmosphere of He, HCl, H2S, H2, O2, and their various mixtures, and the crystal structure of the fired ZnS was analyzed by x-ray diffraction. At 800 °C, the transformation from hexagonal to cubic form occurred slightly in O2 and H2S, markedly in HCl, but hardly at all in He and H2 although NaCl was added. At 1050 °C, the transformation from cubic to hexagonal form occurred easily in all atmospheres except H2 and notably in HCl. The transformation occurred in H2 with added NaCl more easily than in pure HCl. Based on these results, it is concluded that the rate of transformation of a ZnS crystal is influenced both by the formation of defects, which result in the contact reaction between the atmosphere and the surface of the ZnS crystal, and by the bulk diffusion of anions (S2− and O2−).
Auger electron emission micrographic studies of the cleavage surface of graphite single crystal
Authors: Hayakawa Kazunobu , Okano Hiroshi , Kawase Susumu , Yamamoto Shigehiko
Published: February 2004

A new primary beam scanning Auger electron energy analyzer was constructed. The diameter of the primary beam is about 3 μm at 9 keV. Using this apparatus, Auger electron emission microanalysis was carried out on the cleavage surface of a natural graphite single crystal by selecting analyzing points in the sample current image of the specimen surface. In addition, by synchronizing the scanning of the primary beam on the specimen surface with the flying spot of the cathode ray tube, Auger emission micrographs were obtained as the brightness modulation due to a particular Auger spectral line emitted from the specimen. By analyzing the microanalysis spectra, the micrographs, and the sample current images, the chemical composition and the texture of the specimen surface were determined with a spatial resolution of 3 μm.
Shock-compression freezing and melting of water and ice
Authors: Schroeder Ronald C. , McMaster William H.
Published: February 2004

Shock-compression data for water and ice are discussed with respect to freezing and melting. The experimental data show that both 20 °C water and −10 °C ice melt at their calculated Hugoniot melting point. Both ice and water are in the ice-VII state before melting.
Analysis of sputtering discharge by optical and mass spectrometry. II. Platinum and tantalum sputtered in argon/nitrogen mixtures
Authors: Westwood W. D.
Published: February 2004

The gas composition during sputtering of tantalum and platinum in argon-nitrogen mixtures in a dc diode system has been investigated using optical and mass spectrometry. Both methods show that, for sputtering tantalum, the water-vapor pressure is significantly reduced by the addition of nitrogen, although no nitrogen is observed until a flow rate of 0.3 cm3 min−1 is reached. For platinum, however, nitrogen is observed at much lower flow rates and no reduction in the water vapor takes place. After sputtering tantalum in the presence of nitrogen, ammonia is the main residual gas and it is suggested that the reactions required to form it take place at a tantalum surface. For nitrogen flow rates less than 0.3 cm3 min−1, the β-Ta phase is replaced by the bcc phase with a consequent reduction in film resistivity. The nitrogen apparently prevents the incorporation of oxygen in the film, but some nitrogen is probably dissolved in the bcc phase. At flow rates just above 0.3 cm3 min−1, the Ta2N phase is formed and is replaced by the TaN phase at higher flow rates. The increase in resistivity with increasing flow is probably due to the presence of an insulating amorphous nitride phase. The tantalum deposition rate decreases with increasing nitrogen flow because of the reduction in the hydrogen concentration, the replacement of argon by nitrogen as the sputtering species, and, possibly, the formation of nitrides on the cathode. The ratio of the intensity emitted by excited tantalum atoms to the tantalum deposition rate increases rapidly with nitrogen flow and this may be due to the formation of nitrides on the cathode. The film density also decreases from 14.0 to 6.5 g cm−3 as the nitrogen flow rate is increased.
Effect of finite scattering volume and detector geometry on measured electron-impact spectra in crossed-beam experiments
Authors: Bonham R. A. , Wellenstein H. F.
Published: February 2004

Calculations are reported for the effects of finite scattering volume and detector geometry on electron-impact intensity measurements in crossed-beam experiments. The target and projectile beams are assumed to be Gaussian in cross-section shape. Three cases for detector geometry are considered using rectangular apertures. The first case consists of a single rectangular aperture. The second case consists of an additional single slit with slit width perpendicular to the direction of target beam flow located between the scattering volume and the rectangular aperture. The third case consists of two apertures. Correction values for various experimental situations are given and theoretical results for the important case of zero scattering angle are compared with experiment.
Phase equilibria in the system Al–Ga–As–Sn and electrical properties of Sn-doped liquid phase epitaxial AlxGa1−xAs
Authors: Panish M. B.
Published: February 2004

Experimental and calculated phase data for the Al–Ga–As–Sn system are presented. A ``simple solution'' treatment adequately predicts the quaternary from data available from the bounding binary and ternary systems. The distribution coefficient for Al between the solid and liquid increases with increasing Sn concentration in the liquid. For constant Sn concentration in the growth solution, the net electron concentration in solution-grown AlxGa1−xAs decreases with increasing x, particularly near the direct-indirect crossover composition. This occurs primarily because of the deepening of the donor level from ∼ 6 meV in GaAs to at least 66 meV in the indirect gap composition region of AlxGa1−xAs.
Spectral line absorption measurement using optical cavities
Authors: Blanaru D. L.
Published: February 2004

A simple technique using a conventional gas laser with spherical mirrors having identical radii of curvature in the nonoscillating regime for spectral line absorption measurements is described and applications for laser work are suggested. The theory of the measurement carried out in the geometrical optical approach for Doppler-broadened lines was checked experimentally and conditions are specified for which measurement inaccuracies of the order of 1% for the peak value of the line absorption coefficient can be obtained. Since the device provides a fine adjustment of the cavity losses, formation of the diffraction modes could be observed in the preoscillating regime of the optical cavity.
Parameters of electron transfer in InP
Authors: James L. W.
Published: February 2004

Calculation of the Γ minimum nonparabolicity of InP from the band structure shows that Kane's theory, which has been used in all velocity-field calculations, underestimates the nonparabolicity and hence causes understimation of the threshold field. The velocity-field characteristic is predicted to be anisotropic. The effective mass components for the L and X valleys are calculated from the band structure. The deformation potential ΞΓL, derived from photoemission data, is large enough that the two-level model appears adequate for calculation of the threshold field.
Optical properties of electrically insulating granular metal films
Authors: Zeller H. R. , Kuse D.
Published: February 2004

By successive evaporation of metal and dielectric we have made films consisting of many layers of small metal particles insulated from each other. Such films are opaque in the visible and near infrared, but electrically insulating. We have measured the dependence of the optical properties on metal particle size and metal-to-insulator volume ratio. The results can be qualitatively understood in terms of the Maxwell-Garnett theory. Possible technical applications are discussed.
Electroluminescent shifting-peak spectra in GaAs with uniform excitation
Authors: Casey H. C. , Bachrach R. Z.
Published: February 2004

Steady-state and time-resolved spectra have been measured at room temperature for spontaneous emission from the GaAs active layer of a double-heterostructure laser. The closely compensated p-type active layer was heavily doped with Si. The double heterostructure provides carrier confinement and permits observation of spontaneous emission for conditions of uniform excitation. The emission at low levels of excitation was stationary in energy while increasing in intensity. At high levels of excitation, the emission shifts to higher energy while increasing in intensity. These spectra result from radiative recombination in which the injected electrons fill the empty conduction band tails and have been designated here as emission due to the band-filling mechanism. Equivalence between steady-state and time-resolved spectra demonstrated that quasiequilibrium exists within the conduction and valence bands. Carrier distributions and emission spectra were calculated as a function of excitation for valence and conduction band density of states represented by Kane's Gaussian band tails. These calculations showed that the emission for the band-filling mechanism was stationary in energy as the injected electrons filled the conduction band tails. As the tail states were filled, the low-energy emission began to saturate and the emission shifted to higher energy. This emission for band filling is compared with the properties of radiative tunneling.
Linear and nonlinear optical properties of LiInS2
Authors: Boyd G. D. , Kasper H. M. , McFee J. H.
Published: February 2004

LiInS2 is an AIBIIIC2VI ternary semiconductor crystallizing with mm2 symmetry. The useful transparency range is 0.5–8 μ, over which we have measured the refractive indices. The optical nonlinear coefficients for second harmonic generation have also been measured. The nonlinear figure of merit is comparable to that of AgGaS2. Three-frequency collinear phase matching is possible in LiInS2 and is analyzed in some detail. LiInS2 is judged to be a potentially more useful optical nonlinear material than the analogous compound LiGaO2.
Reply to ``Comment on the coefficient of friction of high polymers as a function of pressure''
Authors: Bowers R. C. , Zisman W. A.
Published: February 2004

In a recent paper, Towle has criticized our studies in which we ralated the coefficient of friction for thin solid lubricant films to a pressure effect on the shear strength of the film material. This a rebuttal to that paper.
Shock unloading phenomena in fiber-reinforced composites
Authors: Hopkins A. K.
Published: February 2004

The shock compression and unloading of several simple homogenous binary mechanical mixtures with polyethylene as the matrix is compared to that of an aluminum fiber/epoxy matrix composite. When both of these systems are unloaded from shock states lying in the liquid regime for the matrix, the latter physically separates from the rigid component and exhibits independent motion. The measured free-surface velocity is that of the matrix material and is predicted by an internally adiabatic compression/isentropic expansion model.
Electro-thermomigration in Al/Si, Au/Si interdigitized test structures
Authors: Christou A.
Published: February 2004

Metal migration induced by electric field and temperature gradients has been studied in aluminum-silicon and gold-silicon interdigitized test structures. At current densities of 2×106 A/cm2 and temperature gradients of 75 °C/cm migration occurred across the Si–SiO2 interface. Calculated diffusion profiles show that below 350 °C, mass transport is more rapid with aluminum. At temperatures between 350 and 550 °C, metal migration is more rapid with gold metallization. Metal migration was shown to be a multistaged process without the existence of a unique activation energy.
Anomalous ultrasonic attenuation in Bi12GeO20, Bi12SiO20, and Bi12(Ge0.5Si0.5)O20
Authors: Rehwald Walther
Published: February 2004

In order to study the anomalous ultrasonic attenuation in these compounds, detailed measurements have been performed as a function of temperature, using a variety of frequencies, sound modes, and materials. Their results prove the existence of a selection rule for the interaction mechanism and confirm previous statements of a relaxation process. From symmetry arguments as well as from the observed strong effects of the Ge or Si atoms, respectively, the conclusion was reached that the anomalous attenuation is closely connected to vacancies in the Ge or Si sublattice.
Periodic structures in integrated optics
Authors: Elachi C. , Yeh C.
Published: February 2004

Thin-film dielectric waveguides with a periodic refractive index, a periodic substrate, or periodic surface are studied. The field is determined from Maxwell's equations using Floquet's theorem. The Brillouin diagram and the interaction regions are investigated. The bandwidth and the attenuation coefficients of the interaction regions are given as a function of the optical wavelength. A number of applications in active and passive integrated optics systems are discussed.
Photovoltaic effect in lead selenide p-n junctions
Authors: Chambouleyron I. , Besson J. M. , Balkanski M.
Published: February 2004

Photovoltaic spectra for lead selenide diffused p-n junctions have been studied versus temperature and substrate impurity concentration. The shape of the spectra and its variation with these two parameters can be explained by taking into account the contribution to photovoltage of several mechanisms. At low photon energies, absorption near the junction is dominant. On the high-energy side, the flat response can be assigned to absorption in the substrate material, followed by spontaneous reemission (radiative energy transfer). In the intermediate region, the dip in photoresponse is due to variations in the spatial distribution of photoexcited carriers which are generated in a wide region of chemical impurity gradient. Careful evaluation of those parameters which we measured in our p-n structures fits with the characteristics of PbSe studied by other methods.
Raman cross sections measured by short-pulse laser scattering and photon counting
Authors: Levatter Jeffrey I. , Sandstrom Richard L. , Lin Shao-Chi
Published: February 2004

Using a repetitively pulsed nitrogen laser of 100-kW peak power and 10-nsec duration, the Raman scattering cross sections at 3371 Å for various gas species relative to that of molecular nitrogen have been measured by a gated photon counting technique. The gases studied include N2, O2, CO, CO2, NO, SO2, C3H6, and C3H8. A statistical correction formula has been derived and applied to the apparent count rate to avoid possible errors due to the finite recovery time of the counter and its inability to distinguish between single- and multiple-photon arrival events within the very short time gate. The resultant accuracy of the present measurements is accordingly estimated to be better than ± 5%.
Molecular alignment and conductivity anisotropy in a nematic liquid crystal
Authors: Carr E. F. , Chou L. S.
Published: February 2004

It has been known that the preferred direction of the nematic director for p-azoxyanisole in a low-audiofrequency electric field is not always perpendicular to the field as predicted from the dielectric properties, and this unusual effect is associated with the ionic conductivity. Molecular alignment is related to the conductivity anisotropy by comparing the relative effectiveness of electric and magnetic fields to produce molecular alignment for different values of the ratio of the conductivities parallel and perpendicular to the nematic director.
Thermal conductivity of CdSxSe1−x solid solutions
Authors: Aresti A. , Congiu A. , Manca P. , Spiga A.
Published: February 2004

The thermal conductivity of CdSxSe1−x (0≤x≤1) solid solutions was measured between 100 and 300 °K. Analysis of the experimental data shows that normal processes played an important role in phonon scattering, and that mass and strain fluctuations equally contribute to thermal resistivity in the temperature range studied.
Prismatic dislocation loops on impurity precipitates in magnesium oxide single crystals
Authors: Narayan J.
Published: February 2004

Prismatic dislocation loops b = 1/2〈101〉, were observed around impurity precipitates in as-grown magnesium oxide single crystals with a high percentage of Ca and Al impurities. The loops lay on {101} slip planes. By using the results of the dynamical theory of electron diffraction including absorption and stereo microscopy, the majority of the loops were identified as b = 1/2〈101〉 vacancy type. The possible chemical form of these impurities is discussed in view of the nature of the dislocation loops.
Misfit dislocations in (110), (112), and (113) homoepitaxial silicon crystals
Authors: Tamura Masao , Sugita Yoshimitsu
Published: February 2004

Misfit dislocations generated in (110), (112), and (113) silicon p-on-p+ epitaxial wafers are investigated through x-ray topography. Dislocations observed are of mixed type and arranged along the intersection of the four {111} planes with the specimen surface. The dislocations are formed by slip to relieve the interfacial shear resulting from the misfit.
K x-ray spectra and electronic band structure of MnP
Authors: Nakamori Hiroo , Tsutsumi Kenjiro , Sugiura Chikara
Published: February 2004

The Kβ5 emission and K absorption spectra of Mn in MnP are obtained with a two-crystal spectrometer and a 50-cm bent-crystal spectrograph, respectively. The Kβ5 spectrum consists of a main band and a subband. The high-energy edge of the Kβ5 band coincides with the K absorption edge. This suggests that MnP is a metallike compound. The obtained spectra of MnP are compared with the K spectra of metallic manganese, the P K absorption spectrum of MnP, and the energy-band structure of MnP. The main band and the subband in the Kβ5 emission spectrum correspond to the filled 3d bands of manganese and the 3p band of phosphorus, respectively. The first and the second maxima in the K absorption spectrum correspond to the empty 3d bands (related to the eg orbitals containing some s and p character) and 4p band of Mn, respectively.
Low-frequency flute instabilities of a bounded plasma column
Authors: Rognlien T. D.
Published: February 2004

A study is made of the stability of quasineutral low-frequency (ω ≪ ωci) flute waves in a low-β collisionless plasma column immersed in a uniform axial magnetic field. The column has a Gaussian number density profile and a dc radial electric field. The differential equation which describes the waves is solved both analytically and numerically for the eigenfrequencies and eigenfunctions. For the case of uniform rotation of the column, analytical solutions are obtained to determine the properties of a column bounded by a conducting cylinder. The instability is a centrifugal flute wave for this case. The boundary can be stabilizing or destabilizing for the m = 1 azimuthal mode, depending on its location, while for all other modes, the boundary is stabilizing. For a nonuniformly rotating column, the effects of gradual shear and abrupt shear are considered using numerical solutions. By following the evolution of these modes as the profiles are changed continuously, a unified picture of their behavior is developed. Again the behavior of the m = 1 mode is found to be different from that of the higher-order modes, as illustrated by the m = 2 mode. The m = 1 mode is quite sensitive to the rotation of the column near the boundary, while the m = 2 mode depends more on an average over the column. Also, for abrupt shear, the m =2 mode evolves into a Kelvin-Helmholtz instability, while the m = 1 mode does not.
Instability of electromagnetic surface waves supported by a bounded plasma stream
Authors: Seshadri S. R.
Published: February 2004

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi-infinite region of free space from another semi-infinite region consisting of a plasma streaming parallel to the interface are investigated for the case in which the wave is progressing either in or opposite to the direction of the stream. The behavior of the surface wave is drastically different from the case in which the plasma is stationary. The surface wave has backward-wave regions. For a certain range of frequencies below the plasma frequency, the surface wave undergoes traveling wave amplification in the direction of the stream. When its wave number is in a certain range, the surface wave progressing in a direction opposite to that of the stream is convectively unstable. The characteristics of this surface wave instability are analyzed.
Dynamic response of aluminum to pulsed energy deposition in the melt-dominated regime
Authors: Oswald R. B. , McLean F. B. , Schallhorn D. R. , Oldham T. R.
Published: February 2004

The results of an experimental study of the dynamic response of aluminum exposed to a high-fluence low-energy pulsed electron beam are presented and compared with calculations based on two equations-of-state (EOS) models for metals in the melt-dominated regime. The first model, the widely used classical Mie-Grüneisen EOS, is a simplified scheme in which no thermodynamic distinction is made between solid and liquid phases. The second model - the so-called GRAY EOS recently developed at Lawrence Livermore Laboratories - is a three-phase EOS which provides a more detailed and thermodynamically complete description of metals in the melt region. The experimental studies consisted of measuring the dynamic response of 6061 aluminum to a pulsed 185-keV electron beam for fluences ranging from 15 to 50 cal/cm2, resulting in peak energy depositions of 450–1500 cal/g. The experimental condition produced a mass blow-off which was dominated by mass in the melt state. The response was characterized by simultaneous (for each electron pulse) measurements of impulse, transmitted stress, blow-off velocities, and mass loss. The experimental results were compared with the predicted response to the rapid heating calculated with a hydrodynamic computer code (RIP) in conjunction with the two EOS models. The essential result of the comparison was that after the onset of melting the simple Mie-Grüneisen model fails to give reasonable agreement with experiment, whereas the GRAY EOS provides acceptable agreement with the experimental results. In particular, the prediction of GRAY that the thermal pressure in the melt regime can be described by an effective ``average'' temperature-dependent Grüneisen parameter, which at the completion of melting is approximately 40% higher than the solid Grüneisen value, is clearly confirmed by the experiments. The results demonstrate the necessity of adequately taking melting into account in modeling material response to pulsed energy deposition.
Experimental properties of injection lasers. IV. Modes of large cavity with sawed sides
Authors: Sommers H. S.
Published: February 2004

The article is concerned with determination of the type of modes in wide injection lasers and in particular with identification of the normal modes in the profile of the beam in the plane of the junction. In a cavity 70 μm wide × 120 μm long, with cleaved facets and sawed sides, the modes are found to be those of a rectangular parallelopiped of the same geometry. The smooth lateral profile of the radiated beam is broken into a series of sharp lobes by inserting a low-resolution high-intensity spectrometer between angle scanner and detector. The spectrometer resolution of a fraction of the separation of successive longitudinal mode groups rejects most of the off-axis modes. Longitudinal mode numbers are unambiguously assigned to the lobes in the beam profile, out to 70° from the facet normal, and the dependence of lobe position on longitudinal number identifies the geometry of the modes. Consideration of the lobe widths and irregularities reveals that the coherence width of the laser modes is essentially its geometric width. The experimental value of the index of refraction of the propagating modes is found to be 3.54±0.07 and its normalized dispersion is 0.30±0.06.
Temperature laws for laser-thin-target interaction
Authors: Bonnier A. , Martineau J.
Published: February 2004

An integrated hydrodynamic inhomogeneous spherical model is used to describe the temporal evolution of thin targets under heating by a laser beam. Computer analysis gives temperature laws as a function of characteristic parameters of both target and laser beam. The results indicate a change in the scaling laws for such laser-created plasmas.
Improving the reliability of Nd : glass mode-locked lasers
Authors: Weichel Hugo
Published: February 2004

The evolution of a picosecond optical pulse in a mode-locked Nd : glass laser is primarily affected by the construction of the resonator components. By paying attention to what have been thought of as minor details in the design of the laserhead, such as mounting of the flashlamps and laser rod, virtually 100% reliability and remarkable reproducibility have been achieved. Furthermore, we have studied how the pump power, mirror alignment, and saturable dye concentration affect the reliability and have found that these parameters must be critically controlled if reproducibility is desired.
Temperature dependence of the microwave behavior of polar semiconductors: n-InSb at 134 GHz
Authors: Löschner H. , Kranzer D.
Published: February 2004

In order to study the influence of statistical effects on the microwave behavior of polar semiconductors, power reflection and transmission measurements have been performed on n-type InSb with the aid of a modified reflectometer at 134 GHz in the temperature range from 83 to 170 K. The carrier concentration and the dc mobility were measured by the van der Pauw method. The Boltzmann equation was numerically solved for low dc and ac electric fields. The calculated dc mobility vs temperature curve was adjusted to the experimentally determined curve by a proper choice of the total ionized impurity concentration Ni. Using this value of Ni the power reflection and transmission at 134 GHz were calculated. Good agreement is obtained between experiment and theory, especially for the temperature dependence. It is shown that at 134 GHz the ac behavior of n-InSb cannot be described accurately by Drude's theory.
Uniqueness theorem for a static electric or magnetic field in a saturable medium
Authors: Steele Charles W.
Published: February 2004

A uniqueness theorem for a static electric or magnetic field in an isotropic but saturable medium is presented. We show that if, in a given region, B and H are appropriately related and Maxwell's equations are satisfied, and if over the boundary of that region either normal B or tangential H is prescribed, then both B and H are unique in that region. A similar statement can be made about D and E in an electric field calculation if, in addition, we assume that the region is free of electric charge.
Theoretical strength of a perfect crystal with exponentially attractive and repulsive interatomic interactions
Authors: Milstein Frederick
Published: February 2004

Numerical calculations are made of the theoretical strength of fcc crystals with two-body exponentially attractive and exponentially repulsive interatomic interactions; the crystals are subjected to unconstrained (100) uniaxial tension and compression. The calculations are made from the point of view of mechanical lattice stability; the general theory has been presented in an earlier paper. The numerical values of the parameters characterizing the interatomic interactions were calculated from the elastic moduli C11 and C12 and the stress-free equilibrium value of lattice parameter for Ni; the element Ni was selected for this purpose because (i) the Cauchy condition is not severely violated for Ni, (ii) the correct (i.e., experimental) linear elastic stress-strain behavior is exhibited by the theoretical model of the crystal, and (iii) reasonably good agreement is obtained between theoretically calculated and experimentally observed anharmonic pressure-vs-volume behavior. Calculations are carried out using relatively short-range steep and long-range shallow atomic potential functions; remarkably good agreement is found among results of calculations made wth the different atomic potentials. The theoretical strength and corresponding strain in tension is about 1.6 × 1011 dyn/cm2 and 10.5%, respectively. The modes of lattice failure are examined. Under sufficient compression, the lattice slips into a stress-free bcc structure which appears at a local energy maximum; the bcc structure is mechanically unstable.
Generalized approach to multiphase dielectric mixture theory
Authors: Tinga W. R. , Voss W. A. G. , Blossey D. F.
Published: February 2004

A self-consistent solution for finding the complex dielectric constant of a multiphase mixture with confocal ellipsoidal shell inclusions is presented. Implicit in the solution are the first-order effects of neighboring inclusions, and hence, the high inclusion density limit is approached correctly. The solution contains the special cases of spherical shells, ellipsoids, spheres, disks, and needles. Reasonable agreement of the theory with some experimental data for wet wood is found. The presence of ellipsoidal shells in a mixture gives rise to a much greater separation between the upper and lower bounds of a mixture dielectric constant as compared to the limits obtained for solid ellipsoidal or spherical inclusions.
X-ray anomalous transmission and topography of oxygen precipitation in silicon
Authors: Patel J. R.
Published: February 2004

The perfection of dislocation-free silicon crystals has been followed as a function of heat treatment at 1000°C by x-ray anomalous transmission. For floating-zone silicon crystals carefully grown to exclude oxygen and carbon, the intensity of the x-ray anomalous transmission does not change following heating for several hundreds of hours at 1000°C. This contrasts with previous measurements on floating-zone silicon where the intensity decreased drastically following the same heat treatment. Suitable experiments have ruled out carbon or vacancies as being responsible for the effects observed in the floating-zone crystals. A Czochralski crystal with 7.5 × 1017 cm−3 of oxygen shows a rapid decrease in perfection when heated at 1000°C. The x-ray anomalous transmission is more sensitive to the heat treatment effects in the early stages of precipitation than the usual infrared 9-μm absorption measurements. The defects contributing to the decreased x-ray anomalous transmission have been detected by x-ray section topographs. Although the precipitate has not been directly identified, these and previous experiments allow the conclusion that oxygen clustering is responsible for the heat treatment effects observed. The results are discussed in the light of recent theory on the effect of clustering on x-ray anomalous transmission.
Thermal expansion of alkali halides from 70 to 570 K
Authors: Rapp J. E. , Merchant H. D.
Published: February 2004

The thermal expansion of 15 alkali halides has been investigated from 70 to 570 K. The single-crystal specimens of LiF, LiCl, LiBr, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbI, CsCl, CsBr, and CsI are examined using a high-precision differential dilatometer in conjunction with an electronic micrometer. The results are compared with those available in the literature and are found to be in reasonable agreement. The Grüneisen parameter γ has been calculated using the present thermal expansion data. For a given cation group, the value of γ is very close, but increase in the cation size decreases γ slightly. The indications are that in the temperature range under investigation γ increases very slowly with temperature.
Investigation of acoustic anharmonic effects via acousto-optic interaction
Authors: Torguet R. , Bridoux E. , Rouvaen J. M.
Published: February 2004

We have studied acoustic anharmonic effects in lead molybdate using a 150-MHz fundamental acoustic wave. When sampling the amplitude of the second harmonic acoustic wave with a laser probe, the light scattered by the fundamental acoustic wave may lead to severe mistakes in the determination of nonlinear coupling constants if care is not taken. This measurement can be carried out so as to get not only the true acoustic second harmonic amplitude but also to get an experimental proof of the phase lag −π/2 between second harmonic and fundamental acoustic waves.
Optical properties of aggregated metal systems: Real metals
Authors: Marton J. P. , Lemon J. R.
Published: February 2004

In a previous paper, the simple Maxwell-Garnett theory of aggregated metal systems was analyzed in the free-electron regime for low damping (ωpτ>1). Expressions were derived for the magnitude and resonance frequencies of plasma and conduction resonances as functions of particle constants and the aggregation parameter. In this paper the effect of moderate and high damping (ωpτ≲1) and the effect of a dielectric interparticle matrix with n > 1 is examined, and the results are compared with experiment.
Theory of strip coupled acoustic devices
Authors: Kino Gordon S. , Shreve William R.
Published: February 2004

A theory of the strip coupled acoustic surface wave amplifier, the acoustic surface wave strip coupler, and the strip coupled acoustic surface wave parametric device is given. This theory makes use of a space harmonic expansion and variational techniques to determine the impedance looking into an individual strip. The resulting model accurately predicts the experimental results obtained with strip couplers and indicates that for optimum coupling the ratio of strip width to gap spacing should be unity. Strips can be used to couple from the piezoelectric medium to a semiconductor to make amplifiers and nonlinear signal processing devices. When used in amplifiers, strip coupling should reduce the power dissipation for a given gain by orders of magnitude and greatly increase the gain at low frequencies. In parametric devices, the strips eliminate the need for microscopic air gaps and should increase the processing efficiency by orders of magnitude.
Third-order elastic constants of lithium niobate
Authors: Nakagawa Yasuhiko , Yamanouchi Kazuhiko , Shibayama Kimio
Published: February 2004

The third-order elastic constants of lithium niobate have been measured by small-amplitude ultrasonic waves as a function of applied stress, including the piezoelectric effects.
Dynamic fracture criteria for a polycarbonate
Authors: Curran D. R. , Shockey D. A. , Seaman L.
Published: February 2004

Flat-plate impact experiments were performed on polycarbonate specimens to produce various levels of fracture damage. Nucleation and growth functions for incipient shock damage were deduced from the observed damage and from measured and computed stress histories. These functions allow quantitative prediction of the shock damage produced by arbitrary stress histories in polycarbonate.
Metal oxide absorption coefficients for use in intense laser interaction with solids
Authors: Boni A. A. , Su F. Y.
Published: February 2004

The existence of metal oxides at the surface of a metal irradiated by an intense laser beam leads to partial absorption of the incident radiation in the blow-off vapor due to vibration-rotation bands which exist in the vicinity of the laser frequency. We present calculations for the vibration-rotation bands of SiO, FeO, AlO, and TiO in the 10.6-μ range for application to CO2 laser interaction. The absorption coefficients are calculated by use of a just overlapping line model. The range of validity of the model is established by performing line-by-line calculations in the vicinity of a typical laser line. The absorption coefficients are then supplemented with an equilibrium chemistry model for laser interaction with Al2O3 and SiO2 surfaces. These calculations may be used to establish the importance of surface shielding for cases in which the blow-off vapor exists in the range of temperatures up to about 7000°K.
Laser gain characterization of near-atmospheric CO2:N2:He glows in a planar electrode geometry
Authors: Denes L. J. , Weaver L. A.
Published: February 2004

Temporally and spatially resolved gain measurements are reported for near-atmospheric CO2:N2:He glow discharges in a contoured planar electrode configuration. When suitably preionized by rows of electrically stressed dielectric interfaces, the entire interelectrode volume is filled with a uniform glow discharge for large ranges of capacitor energy, voltage, and gas pressure. The 10.59-μm gain reaches a peak value of 2.8% cm−1 in 2 μsec, and decays exponentially with a 20-μsec time constant in near-optimum laser mixtures of 60 Torr CO2, 180 Torr N2, and 60 Torr He. Peak gain is uniform over the transverse dimensions to within 5%. Mathematical expressions are developed which relate the small-signal gain to the P and R branch rotational quantum numbers in a linear fashion. This analysis shows that for optimized laser conditions the 00°1–10°0 population inversion is [inverted lazy s]1.8×1017 cm−3 with a rotational temperature of [inverted lazy s]400 °K. This corresponds to a maximum 10.6-μm optical storage density of [inverted lazy s]31 J/liter and represents [inverted lazy s]17% of the electrical energy input to the discharge.
Study of excitation transfer in dye mixtures by measurements of gain spectra
Authors: Dienes A. , Madden M.
Published: February 2004

The laser behavior of the Cresyl Violet-Rhodamine 6G dye system is studied by measurements of the small-signal gain spectra for various dye mixtures and pump powers. It is found that most of the pump power absorbed by the Rhodamine 6G is transferred to the Cresyl Violet as useful pump power. The experimental results are in good agreement with a simple theoretical model.
Elastic, magnetic, and electrical properties of pure and lithium-doped nickel oxide
Authors: Notis M. R. , Spriggs R. M. , Hahn W. C.
Published: February 2004

The measurement of Young's modulus as a function of temperature for pressure-sintered lithium-doped nickel oxide was found to be a very sensitive method for the determination of the variation of the Néel temperature with composition. The low-temperature value of Young's modulus was found to increase with increased lithium content and the temperature of the modulus anomaly was found to decrease linearly with increased lithium content. This behavior was interpreted in terms of a localized electron theory of antiferromagnetism. Resistivity measurements agreed with the reported results on single-crystal material. These include a break at the Néel temperature, a lower activation energy at higher temperatures than at lower temperatures, and a decrease in the low - temperature activation energy with increasing lithium content. The combined trends in the modulus and resistivity as a function of temperature and impurity level were interpreted in terms of an electron-acoustic-mode interaction model which predicts an inverse relation between the elastic modulus and the energy difference between the self - trapped and activated electron states. It was concluded that the success of a quantitatively correct localized electron model appears to depend on the development of a theoretical approach which would simultaneously account for both optical - mode and acoustic - mode interactions.
Polarized neutron techniques for the observation of ferromagnetic domains
Authors: Schlenker Michel , Shull C. G.
Published: February 2004

Simple domain structures were observed in iron-silicon and cobalt-iron single crystals by three techniques using polarized neutrons. The first method involves scanning the specimen with a fine beam and measuring the depolarization suffered by the beam after transmission: it can only detect regions where the magnetization direction deviates from the direction of polarization of the beam, and cannot differentiate domains with antiparallel magnetization. The second method, based on the determination of the ratio of the Bragg-diffracted intensities when the polarization of a fine beam is reversed, provides, when the specimen is scanned, a map of the domains. The third technique, polarized neutron diffraction topography, provides photographs of the domain structure. The possibilities of these techniques for the observation of domains within bulk specimens are discussed.
Structural analysis and photoemissive response of the Ge/Cs/O (100) surface
Authors: Goldstein Bernard , Martinelli Ramon U.
Published: February 2004

The Ge (100) surface adsorbs Cs and O2 in the same manner as does the Si (100) surface, but the resulting Ge/Cs/O surface does not exhibit negative electron affinity (NEA). Both Cs and O2 are adsorbed in an ordered way—each adsorbate exhibiting the same 2 × 2 LEED pattern as the clean Ge substrate. Cs must be adsorbed before O2 if the final Ge/Cs/O surface is to be ordered. The spectral photoemission data from the Ge/Cs (100) surface shows a threshold at 1.56 eV, while the threshold of the Ge/Cs/O surface is 1.12 eV, both of which are not band-gap limited. From both the Ge/Cs and the Ge/Cs/O (100) surfaces, photoemission is characterized by hot electron emission over a positive energy barrier at the surface.
Manganese laser
Authors: Chen Che Jen
Published: February 2004

The metallic manganese is vaporized in an alumina tubing in a tantalum heater. The vapor is pumped by utilizing a pulsed current through the tube. The laser power output, laser pulse width, and energy density in the lasant as functions of temperatures of the metal are measured and presented.
Parametric and discharge studies of three-color gas-mix ion lasers
Authors: Ahmed Samir A. , Keeffe William M.
Published: February 2004

The relationship between gas concentration and laser power output is examined for mixed noble gas ion lasers. Specifically, a parametric study was carried out on argon-krypton lasers with cw three-color power outputs of over 3 W, balanced to give white light as defined by CIE illuminant C. It is found that provided total gas density is maintained constant, argon and krypton gases may be mixed at will in ion laser discharges to obtain the required output balance, implying a mutual compatibility of discharge conditions for argon and krypton lasers. This compatibility is explained by showing that at the same gas densitites of argon or krypton, expected electron temperatures are approximately the same. Under these conditions, excitation rates of laser levels are proportional to the fractional gas concentrations.