bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the static yield stress in a binary Lennard-Jones glass
Authors: Varnik F. , Bocquet L. , Barrat J.-L.
Published: February 2004

The stress–strain relations and the yield behavior of a model glass (a 80:20 binary Lennard-Jones mixture) [W. Kob and H. C. Andersen, Phys. Rev. E 52, 4134 (1995)] is studied by means of molecular dynamics simulations. In a previous paper [F. Varnik, L. Bocquet, J.-L. Barrat, and L. Berthier, Phys. Rev. Lett. 90, 095702 (2003)] it was shown that, at temperatures below the glass transition temperature, Tg, the model exhibits shear banding under imposed shear. It was also suggested that this behavior is closely related to the existence of a (static) yield stress (under applied stress, the system does not flow until the stress σ exceeds a threshold value σy). A thorough analysis of the static yield stress is presented via simulations under imposed stress. Furthermore, using steady shear simulations, the effect of physical aging, shear rate and temperature on the stress–strain relation is investigated. In particular, we find that the stress at the yield point (the “peak”-value of the stress–strain curve) exhibits a logarithmic dependence both on the imposed shear rate and on the “age” of the system in qualitative agreement with experiments on amorphous polymers [C. Ho Huu and T. Vu-Khanh, Theoretical and Applied Fracture Mechanics 40, 75 (2003); L. E. Govaert, H. G. H. van Melick, and H. E. H. Meijer, Polymer 42, 1271 (2001)] and on metallic glasses [W. L. Johnson, J. Lu, and M. D. Demetriou, Intermetallics 10, 1039 (2002)]. In addition to the very observation of the yield stress which is an important feature seen in experiments on complex systems like pastes, dense colloidal suspensions [F. Da Cruz, F. Chevoir, D. Bonn, and P. Coussot, Phys. Rev. E 66, 051305 (2002)] and foams [G. Debrégeas, H. Tabuteau, and J.-M. di Meglio, Phys. Rev. Lett. 87, 178305 (2001)], further links between our model and soft glassy materials are found. An example is the existence of hysteresis loops in the system response to a varying imposed stress. Finally, we measure the static yield stress for our model and study its dependence on temperature. We find that for temperatures far below the mode coupling critical temperature of the model (Tc=0.435 in Lennard-Jones units), σy decreases slowly upon heating followed by a stronger decrease as Tc is approached. We discuss the reliability of results on the static yield stress and give a criterion for its validity in terms of the time scales relevant to the problem.
Raman under nitrogen. The high-resolution Raman spectroscopy of crystalline uranocene, thorocene, and ferrocene
Authors: Hager J. Stewart , Zahardis James , Pagni Richard M. , Compton Robert N. , Li Jun
Published: February 2004

The utility of recording Raman spectroscopy under liquid nitrogen, a technique we call Raman under nitrogen (RUN), is demonstrated for ferrocene, uranocene, and thorocene. Using RUN, low-temperature (liquid nitrogen cooled) Raman spectra for these compounds exhibit higher resolution than previous studies, and new vibrational features are reported. The first Raman spectra of crystalline uranocene at 77 K are reported using excitation from argon (5145 Å) and krypton (6764 Å) ion lasers. The spectra obtained showed bands corresponding to vibrational transitions at 212, 236, 259, 379, 753, 897, 1500, and 3042 cm−1, assigned to ring–metal–ring stretching, ring–metal tilting, out-of-plane CCC bending, in-plane CCC bending, ring-breathing, C–H bending, CC stretching and CH stretching, respectively. The assigned vibrational bands are compared to those of uranocene in THF, (COT)2−, and thorocene. All vibrational frequencies of the ligands, except the 259 cm−1 out-of-plane CCC bending mode, were found to increase upon coordination. A broad, polarizable band centered about ∼460 cm−1 was also observed. The 460 cm−1 band is greatly enhanced relative to the vibrational Raman transitions with excitations from the krypton ion laser, which is indicative of an electronic resonance Raman process as has been shown previously. The electronic resonance Raman band is observed to split into three distinct bands at 450, 461, and 474 cm−1 with 6764 Å excitation. Relativistic density functional theory is used to provide theoretical interpretations of the measured spectra.
Atom-bond electronegativity equalization method fused into molecular mechanics. I. A seven-site fluctuating charge and flexible body water potential function for water clusters
Authors: Yang Zhong-Zhi , Wu Yang , Zhao Dong-Xia
Published: February 2004

Recently, experimental and theoretical studies on the water system are very active and noticeable. A transferable intermolecular potential seven points approach including fluctuation charges and flexible body (ABEEM-7P) based on a combination of the atom-bond electronegativity equalization and molecular mechanics (ABEEM/MM), and its application to small water clusters are explored and tested in this paper. The consistent combination of ABEEM and molecular mechanics (MM) is to take the ABEEM charges of atoms, bonds, and lone-pair electrons into the intermolecular electrostatic interaction term in molecular mechanics. To examine the charge transfer we have used two models coming from the charge constraint types: one is a charge neutrality constraint on whole water system and the other is on each water molecule. Compared with previous water force fields, the ABEEM-7P model has two characters: (1) the ABEEM-7P model not only presents the electrostatic interaction of atoms, bonds and lone-pair electrons and their changing in respond to different ambient environment but also introduces “the hydrogen bond interaction region” in which a new parameter klp,H(Rlp,H) is used to describe the electrostatic interaction of the lone-pair electron and the hydrogen atom which can form the hydrogen bond; (2) nonrigid but flexible water body permitting the vibration of the bond length and angle is allowed due to the combination of ABEEM and molecular mechanics, and for van der Waals interaction the ABEEM-7P model takes an all atom–atom interaction, i.e., oxygen–oxygen, hydrogen–hydrogen, oxygen–hydrogen interaction into account. The ABEEM-7P model based on ABEEM/MM gives quite accurate predictions for gas-phase state properties of the small water clusters (H2O)n (n=2–6), such as optimized geometries, monomer dipole moments, vibrational frequencies, and cluster interaction energies. Due to its explicit description of charges and the hydrogen bond, the ABEEM-7P model will be applied to discuss properties of liquid water, ice, aqueous solutions, and biological systems.
Controllable quantum spin precession by Aharonov–Casher phase in a conducting ring
Authors: Shen Shun-Qing , Li Zhi-Jian , Ma Zhongshui
Published: February 2004

We investigate quantum spin transport in a structure of a conducting ring embedded in a textured electric field with two leads, and obtain an exact solution for the problem. The spin precession induced by the Aharonov–Casher phase is studied. It is shown that the spin-polarized current and its polarization orientation can be controlled by the electric field. As a result the modulated polarization orientation is a function of the geometric phase which originates from spin–orbital interaction in the ring.
Temperature tuning of the optical properties of planar photonic crystal microcavities
Authors: Wild B. , Ferrini R. , Houdré R. , Mulot M. , Anand S. , Smith C. J. M.
Published: February 2004

We report on the temperature tuning of the optical properties of photonic crystal (PhC) microcavities. Planar and one-dimensional cavities were made from two-dimensional PhCs etched in GaAs and InP based vertical waveguides. These systems were optically characterized by an internal light source technique. The samples were mounted on a Peltier stage in order to vary the temperature from 20 to 76 °C. Linear dependence of the resonance wavelengths with respect to the temperature is observed with gradients dλ/dT=0.09 and 0.1 nm/°C for GaAs and InP based cavities, respectively. These results are in agreement with theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component.
Tunneling-electron-induced molecular luminescence from a nanoscale layer of organic molecules on metal substrates
Authors: Guo X.-L. , Dong Z.-C. , Trifonov A. S. , Yokoyama S. , Mashiko S. , Okamoto T.
Published: February 2004

Molecular luminescence from an ultrathin layer of free-base porphyrin molecules has been generated by a scanning tunneling microscope on top of a monolayer spacer of perinone derivatives on Cu(100). Tunneling-electron-induced fluorescence spectra are in good agreement with the conventional photoluminescence data of the molecule. The dominant molecular luminescence peak becomes clear and sharp for bias voltages above ∼2.1 V. The perinone monolayer does not emit light because of quenching effects; it acts as a buffer layer to enhance the decoupling of the electronic state of the porphyrin molecules from the Cu substrate. The molecular luminescence from porphyrin is attributed to the hot electron injection excitation. These results demonstrate the feasibility of electrically driven molecular luminescence on metal substrates by a nanoscale probe.
Effects of pressure on the band structure of highly mismatched Zn1−yMnyOxTe1−x alloys
Authors: Shan W. , Yu K. M. , Walukiewicz W. , Beeman J. W. , Wu J. , Ager J. W. , Scarpulla M. A. , Dubon O. D. , Haller E. E.
Published: February 2004

We report photomodulation spectroscopy measurements of the pressure dependence of the optical transition in Zn1−yMnyOxTe1−x alloys that is associated with the lowest Γ conduction band (termed E− subband). The pressure-induced energy shift of the E− transition is nonlinear and much weaker as compared to the change of the direct band gap of Zn0.88Mn0.12Te. The weak pressure dependence of the E− transition can be fully understood based on the band anticrossing model in which the E− subband results from an interaction between the extended ZnMnTe conduction-band states and the localized O electronic states.
DOUBLE PHASE MATCHING OF ACOUSTICALLY INDUCED OPTICAL HARMONIC GENERATION
Authors: Nelson D. F. , Lax M.
Published: February 2004

The concept of double phase matching of a two-step contribution to acoustically induced optical harmonic generation (AIOHG) is proposed. For plane waves the doubly phase-matched AIOH grows as the fourth power of the crystal length. Its intensity can be 109 times as strong as that produced by single phase matching under reasonable conditions.
SPECTRAL NARROWING OF DYE LASER OUTPUT BY INJECTION OF MONOCHROMATIC RADIATION INTO THE LASER CAVITY
Authors: Erickson L. E. , Szabo A.
Published: February 2004

Spectral narrowing of dye-laser output by injection of monochromatic radiation is reported. The pulsed N2-pumped exciplex laser was narrowed from 400 to 0.0016 Å with injection of 50 mW of 5145-Å light with no change in total power output.
A FAR-INFRARED COUPLED-CAVITY INTERFEROMETER
Authors: Peterson R. W. , Jahoda F. C.
Published: February 2004

A coupled-cavity HCN laser interferometer (337 μ) is described. Phase-shift sensitivity of 1/20 fringe (∫n dl=1.6×1013 cm−2 for free electrons) has been achieved. The present time resolution of 6 μsec is determined by the available mechanical motion and is not the limit of the interferometer capability. The use of this laser for measuring a low-density transient plasma is illustrated.
ANOMALOUSLY HIGH NONLINEAR OPTICAL EFFECTS IN m-NITROANILINE
Authors: Southgate P. D. , Hall D. S.
Published: February 2004

High values of electro-optic coupling and second-harmonic generation coefficients have been found in m-nitroaniline; Miller's Δ coefficients are higher than any previously reported. The shape of the absorption band rather than a favorable bond-orientation geometry appears to be responsible.
REDUCTION OF DOPPLER BROADENING OF SPECTRAL LINES IN FAST-BEAM SPECTROSCOPY
Authors: Stoner John O. , Leavitt John A.
Published: February 2004

We show that the Doppler broadening, which arises in a fast-beam light source because of the high speed of the emitters and the nonzero acceptance angle of the spectrometer, can often be practically eliminated by proper adjustment of the spectrometer.
POLY(METHYL METHACRYLATE) DYE LASER WITH INTERNAL DIFFRACTION GRATING RESONATOR
Authors: Kaminow I. P. , Weber H. P. , Chandross E. A.
Published: February 2004

We describe a compact monochromatic (0.1 Å) dye laser, which consists of a pair of Bragg phase gratings photodielectrically induced inside a bulk sample of poly (methyl methacrylate), PMMA, doped with rhodamine 6G. The laser frequency can be selected by choice of grating period from the usual broad (∼200 Å) emission spectrum of the dye.
ASSIGNMENTS OF THE FAR-INFRARED SO2 LASER LINES
Authors: Hubner Gunter , Hassler J. C. , Coleman P. D. , Steenbeckeliers Guy
Published: February 2004

Nine out of ten observed laser transitions in SO2 have been assigned involving two irregular Fermi interactions between ν1, K−1=14 and 2ν2, K−1=16 at J=26 and 27. From these assignments, a new laser line at 206 μm was predicted and found.
CHARGED-PARTICLE RADIATION DAMAGE OBSERVED AS DIMPLING OF THIN SILICON TARGETS
Authors: Meek R. L. , Gibson W. M. , Sellschop J. P. F.
Published: February 2004

When thin uniform silicon targets are bombarded with energetic ions, macroscopic deformation of the target occurs in the irradiated region. This deformation, which is euphemistically termed a ``dimple'', may be interpreted as a radiation-induced lattice expansion. Measurement of the amount of deformation allows lattice expansion to be determined with a sensitivity comparable to or better than the most sensitive existing methods. Measurements on silicon irradiated at room temperature by 1.8-MeV He ions show that the lattice expansion at low flux increases essentially linearly with fluence below about 5×1016 He ion/cm−2, whereupon it increases more rapidly until saturation starts to occur at an order-of-magnitude higher fluence. Isochronal annealing results are discussed.
HOLOGRAPHIC PATTERN FIXING IN ELECTRO-OPTIC CRYSTALS
Authors: Amodei Juan J. , Staebler David L.
Published: February 2004

This paper describes the results of an investigation into techniques for obtaining erasure resistant holograms in electro-optic crystals. The most successful approach made use of thermally activated ionic drift during or after recording. The samples are heated for about 30 min at 100°C to obtain optically nonerasable holograms with as much as 50% diffraction efficiency in LiNbO3 or in doped Ba2NaNb5O15.
EFFICIENT WIRE-GRID DUPLEXER POLARIZER FOR CO2 LASERS
Authors: Cheo P. K. , Bass C. D.
Published: February 2004

A chromium wire-grid duplexer polarizer for CO2 lasers has been developed using holographic and chemical etching techniques. The reflection and transmission measurements show reasonably good agreement with the theory.
HIGH AVERAGE POWER OPERATION AND NONLINEAR OPTICAL GENERATION WITH THE Nd:YAlO3 LASER
Authors: Massey G. A. , Yarborough J. M.
Published: February 2004

Using a Nd: YAlO3 rod 3 in. long, we have obtained 75-W continuous output at 1.08 μ and 35 W at 1.0645 μ, both linearly polarized. Laser action has been obtained at five wave-lengths between 1.06 and 1.10 μ and at two lines near 1.34 μ at room temperature. The preferred polarization for each of these lines has been determined. Intracavity second harmonic and parametric generation with LiNbO3 in this laser have produced a 3-W average in a single beam at 5400 Å and a 775-mW average at 2.16 μ. The laser is free from depolarizing thermal birefringence at pump powers up to 4.5 kW.
LOW-THRESHOLD LOC GaAs INJECTION LASERS
Authors: Kressel H. , Lockwood H. F. , Hawrylo F. Z.
Published: February 2004

We report new results with the large optical cavity (LOC) injection lasers previously described. It is shown that by narrowing the n region adjacent to the junction, the threshold current decreases without decreasing the differential quantum efficiency. Furthermore, epitaxial growth of all layers was used, and diffusion was avoided. Fabry-Perot mode threshold current densities as low as 1700 A/cm2 were obtained with differential quantum efficiencies of about 50% and power conversion efficiencies of 20% at room temperature.
ENHANCEMENT OF SUPERCONDUCTIVITY IN THIN INDIUM FILMS
Authors: Garland M. M.
Published: February 2004

The effect of elastic tensile stress on the superconducting transition temperature of thin indium films is investigated through the use of specially fabricated substrates. It is found that the transition temperatures may be elevated as much as 0.91 °K above the bulk value.
ACOUSTIC WAVES IN BERYLLIUM OXIDE CRYSTAL
Authors: Hagon P. J. , Austerman S. B.
Published: February 2004

Experimental results are reported on the coupling between electromagnetic signals and acoustic waves in beryllium oxide crystals via interdigital transducers deposited on a natural y face of a BeO crystal. The transducers are oriented to propagate acoustic waves along the z axis.
IMAGE AMPLIFICATION BY DYE LASERS
Authors: Hänsch T. W. , Varsanyi F. , Schawlow A. L.
Published: February 2004

Wide-angle high-gain image amplification has been achieved with several organic dye solution lasers. Rhodamine 6G, rhodamine B, or fluorescein disodium salt in ethanol, side pumped by a nitrogen laser, were used. With excitation pulses of 10−4 J and an active volume of about 1.3×0.1×0.1 mm3, a single-pass gain of 23 dB/mm and a diffraction-limited resolution of more than 104 distinguishable spots have been observed.
TYPE S BULK NEGATIVE DIFFERENTIAL CONDUCTIVITY IN n-InSb
Authors: Dick C. L. , Ancker-Johnson B.
Published: February 2004

The relationship between type S and type N (Gunn effect) bulk negative differential conductivity (BNDC) is shown in n-InSb at 77 K and atmospheric pressure. The results of conduction measurements and of radiative recombination measurements, both in time and space, shown that an S-BNDC is created in the wake of a propagating high-field domain and that the large currents associated with the S-BNDC are caused by strong impact ionization in the domain.
Q-SWITCHED LASER WITH CONTROLLABLE PULSE LENGTH
Authors: Young J. F. , Murray J. E. , Miles R. B. , Harris S. E.
Published: February 2004

Experimental results of a recently proposed technique for obtaining Q-switched laser pulses of controllable length are presented. A lithium iodate doubling crystal inside the cavity of a Nd: YAG laser running at 0.946 μ is used to provide both output coupling and an easily adjustable, nonlinear loss mechanism. Controllable pulse lengths in the range of 200 nsec to 1 μ at 0.473 μ have been achieved at nominally constant energy.
STIMULATED EMISSION IN A PERIODIC STRUCTURE
Authors: Kogelnik H. , Shank C. V.
Published: February 2004

We have investigated laser oscillation in periodic structures in which feedback is provided by backward Bragg scattering. These new laser devices are very compact and stable as the feedback mechanism is distributed throughout and integrated with the gain medium. Intrinsic to these structures is also a gratinglike spectral filtering action. We discuss periodic variations of the refractive index and of the gain and give the expression for threshold and bandwidth. Experimentally we have induced index periodicities in gelatin films into which rhodamine 6G was dissolved. The observed characteristics of laser action in these devices near 0.63 μm are reported.
OBSERVATION OF INTENSE SUPERRADIANT EMISSION IN THE HIGH-GAIN INFRARED TRANSITIONS OF HF AND DF MOLECULES
Authors: Goldhar J. , Osgood R. M. , Javan A.
Published: February 2004

Intense stimulated emission (superradiance) is obtained in several high-gain transitions of HF and DF molecules. The narrowing of the linewidths of the high-gain transitions are observed in detail. Pulsed energy and peak powers are comparable with those obtainable in a similar transverse CO2 laser.
MULTILAYER THIN-FILM ANALYSIS BY ION BACKSCATTERING
Authors: Picraux S. T. , Vook F. L.
Published: February 2004

Multilayer polycrystalline Er, Sc, or V layers, 500–20 000 Å thick, on Kovar or sapphire substrates were studied using 2-MeV He+ ion backscattering. Underlying, as well as surface layer, average thicknesses were measured with a sensitivity of 200 Å. In addition, results were obtained on interfacial diffusion, film thickness variations, and the depth distribution of heavy impurities.
EFFICIENT, SINGLE-MODE, cw, TUNABLE SPIN-FLIP RAMAN LASER
Authors: Brueck S. R. J. , Mooradian A.
Published: February 2004

Continuous operation of a spin-flip Raman laser in InSb using a CO pump laser has been achieved in a single longitudinal and single transverse mode with over-all power conversion efficiency in excess of 50% and output power in excess of 1 W. Measured threshold powers were less than 50 mW.
GAIN OF CO2 GASDYNAMIC LASERS
Authors: Lee George , Gowen Forrest E.
Published: February 2004

Experimental measurements and theoretical calculations of gain for a cw CO2 gasdynamic laser were made for a CO2, N2, He mixture. A temperature range of 800 to 2000°K, pressure range of 2 to 16 atm, and a complete range of gas mixtures were studied. Optimum gain was achieved at a temperature of 1600°K, a helium mole fraction near 40%, and a CO2 mole fraction of approximately 20%. Gain was essentially independent of pressure.
TEMPERATURE DEPENDENCE OF THE ATTENUATION OF MICROWAVE FREQUENCY ELASTIC SURFACE WAVES IN QUARTZ
Authors: Budreau Alan J. , Carr Paul H.
Published: February 2004

The attenuation of elastic surface waves propagating in vacuum along the x axis of Y-cut quartz has been measured from 4.2 to 300 K over the frequency range 0.57–1.54 GHz. The temperature-dependent propagation loss was 2.2 dB/μsec at 1.0 GHz. At temperatures below 23 K, the attenuation was ωT4, while above 70 K it was temperature-independent and in good agreement with the predictions of the viscosity model.
SPACE-CHARGE RECOMBINATION OSCILLATIONS IN DOUBLE-INJECTION STRUCTURES
Authors: Weber Willes H. , Ford G. W.
Published: February 2004

The small-signal impedance is derived for a double-injection structure operating in the low-injection square-law regime. Space-charge effects are found to be essential. Spontaneous voltage oscillations are found to occur above a threshold voltage Vth. The theory gives quantitative agreement with experimental results for Au-doped Si p-i-n diodes. These include the temperature dependence of Vth and the threshold frequency as well as the voltage dependence of the frequency above threshold.
MEASUREMENT OF PICOSECOND PULSE SHAPE AND BACKGROUND LEVEL
Authors: Auston D. H.
Published: February 2004

The approximate shape and the background level of picosecond pulses from an Nd:glass laser have been determined by the measurement of a correlation function which is sensitive to pulse shape and asymmetry. A combination of second harmonic generation and a phase-matched four-photon parametric interaction was used to obtain the correlation function. The pulses were found to be symmetric with a mean width of 12 psec and have an average background level of 10−4.
SURFACE WAVES CIRCULATING ON PIEZOELECTRIC SUBSTRATES
Authors: Cho Frederick Y. , Hunsinger Bill J. , Lawson Ronald L.
Published: February 2004

Surface waves circulating on closed paths have been observed on lithium niobate and quartz crystals. More than 12 circulations on a 25-μsec quartz delay line have been achieved providing processing times in excess of 300 μsec. Surface-wave attenuation and reflection which vary with the surface curvature are reported.
SOME APPLICATIONS OF ION-ELECTRON IMAGE CONVERSION IN FIELD ION MICROSCOPE STUDIES OF SURFACE REACTIONS
Authors: Cranstoun G.K.L. , Pyke D.R.
Published: February 2004

An ion-electron image converter has been applied to field ion studies of surface reactions. Argon imaging has been used to study oxygen and carbon monoxide adsorption on tungsten while the effect of using the reactive imaging gases, oxygen, nitrogen, and carbon monoxide, has also been investigated. The reaction of nitrogen is of particular interest in the context of field-induced rearrangement processes.
IMAGE-CONVERTER STREAK CAMERA WITH PICOSECOND RESOLUTION
Authors: Schelev M. Ya. , Richardson M. C. , Alcock A. J.
Published: February 2004

A streak camera incorporating a standard, readily available, image-converter tube has been developed and used for the direct measurement of 1.06-μ-wavelength picosecond pulses generated by a mode-locked neodymuim: glass laser.
INFLUENCE OF DISCHARGE PROPERTIES ON CO2 LASER GAIN
Authors: Wiegand W. J. , Fowler M. C. , Benda J. A.
Published: February 2004

The radial variation of small-signal gain α0 at 10.6 μm was measured in a cylindrical, electrically excited CO2 laser amplifier. The radial-gain profile changed markedly with increasing current. This was interpreted in terms of the dependence of gain on electron density and gas temperature. A modified Schottky analysis of the positive column was used to characterize the discharge properties. Values of electron density and gas temperature thus obtained were combined with the reported dependence of α0 on these parameters permitting calculation of the radial variation of α0. Comparison of calculated and measured values of α0 yielded good quantitative agreement, indicating that the analytical model accurately represents the features of the important physical phenomena which influence small-signal gain. These results emphasize the necessity of maintaining a low gas temperature to achieve maximum laser performance.
TRANSVERSE SPATIAL DIFFUSION OF PHASE-DISPERSED PULSES
Authors: Kim Dae M. , Shah Pradeep L. , Rabson T. A.
Published: February 2004

The transverse spatial diffusion of phase-dispersed pulses is shown to have significant effects on the theoretical limit of the dechirped pulse duration, output-beam cross section, and its TPF display. The possibility of recovering temporal and spectral contents of pulses from its two-dimensional TPF is discussed.
SIMULTANEOUS INTRACAVITY FREQUENCY DOUBLING AND MODE LOCKING IN A Nd: YAG LASER
Authors: Hitz C. B. , Osterink L. M.
Published: February 2004

An efficient internally frequency-doubled mode-locked Nd:YAG laser has been operated. An interaction between the intracavity harmonic generation and mode locking, which results in a lengthening of the mode-locked pulse and a corresponding decrease in fundamental circulating power, has been observed with this laser. The laser makes use of an intracavity harmonic mirror to produce 1.5 W of 0.53-μ power in the output beam. A significant decrease in laser noise is observed when the laser is mode locked.
ABSORPTION IN CO2 AT 10.6 μ WITH ROTATIONAL LINE OVERLAP
Authors: Christiansen W. H. , Mullaney G. J. , Hertzberg A.
Published: February 2004

The results of a calculation and measurement of the absorption of 10.6-μ laser radiation by CO2 at high pressures are described. It is shown that the effect of rotational line overlap becomes significant at pressures slightly greater than 1 atm. At 8 atm, for example, the calculated absorption coefficient is twice that without including line overlap. Measurements, however, indicate a larger effect than is predicted.
CONVOLUTION AND TIME INVERSION USING PARAMETRIC INTERACTIONS OF ACOUSTIC SURFACE WAVES
Authors: Luukkala M. , Kino G. S.
Published: February 2004

We report on the observation of acoustic convolution, time inversion, and electronically variable delay in real time using 105- and 220-MHz surface acoustic waves in YZ-cut LiNbO3 delay rods. The time inversion is a special case of correlation, where a short ``pip'' pulse will create a reflection in time for the injected input signal pulse. The conversion losses in the processing were 64–74 dB.
Discussion of the Schwarz-Hora Effect
Authors: Hadley G. R. , Stanek E. J. , Good R. H.
Published: February 2004

In the Schwarz-Hora effect, an electron beam passing through a crystal is modulated by laser light and then reproduces the light when it strikes a nonluminescent target. In this paper, the theory for the modulation process is developed using Born approximation to second order. A mechanism for light production at a nonresonant target is also discussed.
Frequency Locking of Laser Oscillators by Injected Signal
Authors: Wang Charles C.
Published: February 2004

The condition for frequency locking of laser oscillators by an externally injected signal is derived. It is shown that this condition is characteristically the same as that derived by Van der Pol in 1934 for low-frequency (audio and radio frequency) oscillators. Our results differ from those of a previous analysis.
Effect of Tensile Stress on the Domain-Nucleation Field of Iron Whiskers
Authors: Self W.B. , Edwards P.L.
Published: February 2004

For an infinitely long iron rod of rectangular cross section with a [100] axis, and which has been magnetized in the [100] direction, theory predicts that an opposing field of about 565 Oe is required to reverse the direction of its magnetization, and that this reversing field increases linearly with axial stress. The proportionality constant relating the reversing field (nucleation field) to the stress is 3λ100/Ms, where λ100 is the saturation magnetostriction constant in the [100] direction and Ms is the saturation magnetization. Iron whiskers may be grown with a rectangular cross section and with the axis in the [100] direction. DeBlois and Bean studied the nucleation field at zero tension in such whiskers and found that in some parts of some whiskers the nucleation field approached the theoretical value. For convenience we call these ``ideal'' parts of the whiskers. We have studied the relationship between nucleation field and stress for ideal parts of whiskers and have found the proportionality constant to be 2.94 ± 0.32 Oe/kg/mm2, in reasonable agreement with the value obtained using the literature values of λ100 and Ms.
EuO Films Doped with Fe and Gd
Authors: Ahn K. Y.
Published: February 2004

EuO films doped with Fe and Gd+++ raise the Curie temperature to ≳200 °K (from 70°K for EuO). The magnetic moment is slightly reduced to 200 emu/g (vs 232 emu/g for EuO). The characteristic optical absorption band, which is due to an electronic transition from 4f to 5d levels of Eu++ ions, remains unchanged with the peak absorption of 2.4×105/cm at 5800 Å. The longitudinal Faraday rotation at 6328 Å with an incident angle of 65° is 1.9×105 and 1.4×105 deg/cm at 7.0 and 77°K, respectively. Films deposited on several types of glasses possess square hysteresis loops with higher values of Hc (86 ∼ 100 Oe at T<10°K and less than 53 Oe at T=77°K), both of which are essential for device applications.
X-Ray Study of Lithium Precipitation in Germanium
Authors: Thomas J. E. , Stuber A. B. , Dearlove J. W.
Published: February 2004

Lithium precipitation in single crystals of germanium has been found to decrease the Borrmann x-ray integrated intensities by as much as an order of magnitude. The anomalous transmission for the 220 reflection with CuKα and MoKα radiation for crystals diffused with lithium and heat treated at different temperatures was measured and found to be dependent upon the temperature of heat treatment. The time dependence of the lithium precipitation after quenching the sample has been observed by x-ray transmission and compared with the time dependence observed by electrical resistivity. The x-ray intensity vs time measurements indicate that the precipitation is nearly complete at the time the resistivity shows the precipitation to be in the initial stages.
Effects of Temperature Inhomogeneity on Resonant Behavior of Plasma Column in the Presence of an Axial Magnetic Field
Authors: Germain R. L. St. , McIntosh R. E.
Published: February 2004

The effects of thermal inhomogeneities and a weak axial magnetic field on the resonant behavior of a plasma column at microwave frequencies are treated in this paper by extending the analysis of Parker, Nickel, and Gould. Temperature inhomogeneities are assumed for our model that yield shifts in the resonant spectra that agree with experiment. These shifts are ascribed to alterations in the electron number density and temperature profiles resulting from the magnetic field.
Interaction of Accelerating High-Current Electron Beams with External Magnetic Fields
Authors: Hammer D. A. , Oliphant W. F. , Vitkovitsky I. M. , Fargo V.
Published: February 2004

When the current and current density of electrons accelerated in the anode-cathode gap of a field emission tube reach sufficiently high values, the induced self-magnetic field begins to dominate the electron trajectories. As a result, the spatial distribution of electrons arriving at the anode becomes strongly peaked in the center of the anode. It has been found possible to prevent such beam collapse with relatively modest external magnetic fields. The field is applied parallel to the electron flow (perpendicular to the anode plane). A scaling law which determines the necessary field strength based on a simple orbit model is found to agree with experimental results over a wide range of electron-beam parameters.
Thermoluminescence in Natural Calcium Flouride as a Dosimeter for Terrestrial Solar Ultraviolet Radiation
Authors: McCullough Edwin C. , Fullerton Gary D. , Cameron John R.
Published: February 2004

Transferred thermoluminescence (TL) in natural calcium fluoride (CaF2:nat) has been investigated as a potential dosimeter of terrestrial solar ultraviolet radiation. Linearity, longterm stability, and spectral sensitivity are among the properties investigated. Relative merits of direct transfer TL vs an upper-trap sampling technique have been ascertained. Application of CaF2:nat as a dosimeter of erythemally effective solar energy has been investigated. The technique provides a convenient and reliable method of uv radiation dosimetry.
Circular disclinations and interface effects
Authors: Kuo H. H. , Mura T.
Published: February 2004

The elastic fields of a circular wedge disclination and a twist disclination in the two-phase materials and a twist disclination in a plate are given. The elastic strain energies and forces on the loops are then obtained to arrive at the studies of the interface effects on the loops.
Structure of electroplated and vapor-deposited copper films. II. Effects of annealing
Authors: Gangulee A.
Published: February 2004

The effects of annealing on some structural parameters of electroplated and vapor-deposited copper films have been investigated by x-ray diffraction and electrical resistivity measurements. The results can be described in terms of two annealing stages. Stage I, occuring only in electroplated films in the temperature range 25–200°C, is characterized by annealing out of twins due to the diffraction and electrical resistivity measurements. The results can be described in terms of two molecules. Stage II, occuring above 200°C, is characterized by annealing out of dislocations and growth of particle sizes. The kinetics of the annealing stages are discussed.
Magnetic focusing of a relativistic electron beam: theory
Authors: Freeman J. R. , Poukey J. W.
Published: February 2004

Computer-simulation techniques have been used to study the interaction of a relativistic electron beam and a mirror magnetic field. A charge-neutralized steady-state model with self-consistent magnetic fields was used to simulate the drift-tube region. Comparisons are made between experimental results, adiabatic calculations, and the computer simulation for the electron distribution at the peak of the mirror field. The dependence of these results on the mirror ratio and beam-entrance conditions is presented.
Experimental studies of injection lasers: spontaneous spectrum at room temperature
Authors: Sommers H. S.
Published: February 2004

The current dependence of the spontaneous and coherent intensities and differential intensities from GaAs injection lasers operated at 300 K is reported. A compensated material with single heterojunction and a low-doped double heterojunction unit were studied. While the spontaneous intensities rise smoothly with current at all power levels, the differential intensities show structure associated with onset of lasing. At threshold there is a sharp cusp, indicating a change in the internal dynamics. The data are found to be consistent with 100% radiative recombination but do not exclude nonradiative transitions. New features are negative differential intensity of lasing; a logarithmic increase of Fermi level with current in the lasing region; and marked differences of the spreading of the lasing spectrum and of the current saturation of the two lasers.
Preparation and optical and magneto-optical properties of samarium chalcogenide thin films
Authors: Suryanarayanan R. , Paparoditis C. , Ferré J. , Briat B.
Published: February 2004

We report on the preparation, structure, and optical and magneto-optical properties of the NaCl-type SmSe and SmTe films, as well as the chalcogen-rich compounds crystallizing in a bcc Th3P4-type structure. Magnetic circular dichroism has been used to help in resolving the absorption spectra as well as to ascertain the singlet nature of the ground state of SmSe and SmTe; the presence of Sm3+ is thus ruled out in these materials. The two absorption peaks observed at 1.2 and 2 eV for SmTe and 1.03 and 1.85 eV for SmSe are identified as transitions arising from 4f6(7F)→4f5(6H)5 d(t2g) and 4f6(7F)→4f5(6F)5 d(t2g), respectively.
Photoinduced voltage-decay characteristics of dye-sensitized poly-N-vinylcarbazole
Authors: Sato Hisanao , Ikeda Mitsusuke
Published: February 2004

Measurements of the photoinduced voltage-decay of dye-sensitized polyvinylcarbazole (PVK) films are reported. A reaction product of a benzopyrylium salt and a benzopyrane is, as the sensitizing dye, uniformly dispersed in the PVK films. The voltage-decay characteristics are analyzed on the basis of a model assuming that holes are generated by an electron transfer from PVK to photoexcited dyes. The model is confirmed by this analysis and by comparing the voltage-decay rate of the uniformly sensitized films with that of a double-layer film consisting of an undoped PVK layer and a very thin dye-sensitized PVK layer. The quantum efficiency of photogeneration of holes is found to increase linearly with the electric field and is estimated to be 0.52 at 106 V/cm. The mean range of holes at 106 V/cm is longer than 11 μ for the films containing less than 1.6 weight parts of the dye relative to 100 weight parts of PVK. The range decreases with the increase in the dye concentration.
Spontaneous and stimulated photoluminescence on nitrogen A-line and NN-pair line transitions in GaAs1−x Px : N
Authors: Holonyak N. , Dupuis R. D. , Macksey H. M. , Craford M. G. , Groves W. O.
Published: February 2004

In accord with recent absorption measurements, photoluminescence measurements on crystals grown from a Ga solution, as well as on some vapor epitaxial crystals, indicate that the A line in GaAs1−x Px : N is higher in energy than formerly believed. Also, the NN-pair emission peak (ENN) has been determined more accurately relative to the A-line peak (EN), and relative to EΓ and Ex. For crystal composition x less than 0.9, only a single NN-pair emission band is observed with ENN = EΓ at x ≈ 0.30. The A-line is broad (⩾ 50 Å) with EN = EΓ at x ≈ 0.40. For EN ≈ EΓ or ENN ≈ EΓ the recombination probability on transitions involving N traps may be resonantly enhanced. If EΓ is close to or degenerate with EN or ENN, carrier reemission from N traps to the conduction band is fast, and stimulated emission involving N or NN trap centers can lead to line narrowing because the excess electron population can readjust rapidly between trap centers and the Γ conduction band.
Anisotropic bending during epitaxial growth of mixed crystals on GaAs substrate
Authors: Nagai Haruo
Published: February 2004

Crystals of GaxIn1−xAs and GaAsxP1−x were deposited on GaAs substrate from the vapor phase, and the deformation properties of these systems accompanying the heteroepitaxial growth were investigated. When the crystal surface of the substrate was {100}, it was found that there was an evident anisotropy of bending in the directions of 〈110〉 and 〈110〉, and this phenomenon cannot be explained by the simple bimetal model. The influence of the crystalline surface of the substrate on the deformation was also checked.
Diffusion theory of the response of pyroelectric detectors
Authors: van der Ziel A. , Liu S. T.
Published: February 2004

It is shown that the diffusion theory of the response of pyroelectric detectors gives a voltage response to modulated radiation that differs insignificantly from the results obtained for the uniformly heated lumped model if the back face of the detector has a low emissivity.
Low-temperature equation of state for amorphous polymer glasses
Authors: Simha R. , Roe J. M. , Nanda V. S.
Published: February 2004

A configurational partition function is developed from cell theory in the harmonic approximation to the cell potential, and given in the quantum formulation. The frequency is an explicit function of volume, and the intermolecular Grüneisen parameter of the Einstein system has an approximate value of three which varies but slightly with volume. Formal expressions for the corresponding Debye system are also presented. The theory is applied to our dilatometric measurements at liquid-helium temperatures and atmospheric pressure on three classes of amorphous polymers, namely, polystyrene and a methyl derivative, a series of methacrylates with varying side chains, and three engineering plastics. It turns out that the reduced quantum temperature assumes a universal value and thus a low-temperature principle of corresponding states obtains. The theoretical thermal expansivities are in good accord with experiment up to a reduced temperature of 4×10−3, corresponding to actual temperatures between 53 and 71 K for the above polymers. Thereafter, and well within the expected applicability of the harmonic approximation, systematic departures from the low-temperature principle of corresponding states as well as the theory appear. These are discussed in terms of available information on location and intensity of low-frequency mechanical relaxation processes.
Influence of diluent mobility on the plasticization of polymers
Authors: Petrie S. E. B. , Moore R. S. , Flick J. R.
Published: February 2004

In an attempt to formulate a general picture of the influence of diluents on the physical properties of polymers without invoking specific molecular characteristics of the diluents, a systematic study has been undertaken of the mobility of both the polymer and the diluent in polymer-diluent systems, and of the resulting effects on the physical properties of these systems. In dynamic mechanical and dielectric loss studies of polymer-diluent systems, the influence of the mobility of the diluent on the background loss as well as on the loss associated with subsidiary relaxation transitions has been followed as a function of temperature and correlated with the temperature dependence of the modulus, over temperature ranges which include the low-temperature γ and β transitions. The temperature ranges of plasticization and antiplasticization have been established for bisphenol A polycarbonate and atactic polystyrene plasticized with various phthalates and chlorinated biphenyls and terphenyls, which were selected to have a wide range of glass transition temperatures and plasticizing efficiencies.
Morphology of high-strength transparent polyethylene prepared under controlled conditions
Authors: Krueger D. , Yeh G. S. Y.
Published: February 2004

Highly oriented transparent polyethylene exhibiting a sixfold improvement in tensile yield strength has been prepared under ordinary pressures by shearing molten polyethylene between two concentric cylinders at rates between 0.4 and 10.0 sec−1 and at temperatures between 129 and 135°C. Our results, based on observed changes in volume and shear stress, show that a transparent polyethylene sample was obtained only when crystallization occurred during the shearing process and further that transparency was greater for samples containing greater fractions of strain-crystallized polyethylene. The major factor controlling the onset of crystallization was found to be the amount of total strain which increased with increasing crystallization temperature. To understand its transparency, electron microscopy and x-ray studies were carried out on polyethylene of various degrees of transparency. Results showed that transparent polyethylene contains perpendicularly well-oriented lamellae (380–400-Å spacing) with limited lateral dimensions (400–2000 Å); whereas polyethylene of increasing opaqueness contains lamellae (285-Å spacing) oriented more or less perpendicular to the flow direction, but with much larger lateral dimensions (1000–10 000 Å).
Attenuation and amplification of acoustic waves in semiconductors in the presence of strong fields
Authors: Sharma Satish
Published: February 2004

Using the Boltzmann equation we derive the expressions for the conductivity and diffusion tensor for a nondegenerate semiconductor which are valid for arbitrary values of the dc field. Following Yamashita and Watanabe, the distortion of the isotropic part of the distribution function has been taken into account. The acoustic-phonon scattering has been considered as the sole mechanism of electron scattering. The absorption coefficient has been calculated numerically and its variation with dc electric field studied for various values of ql. It is seen from the results that values of absorption coefficient are considerably changed by using a non-Maxwellian distribution function.
Stacking faults in (100) epitaxial silicon caused by HF and thermal oxidation and effects on p-n junctions
Authors: Drum C. M. , van Gelder W.
Published: February 2004

Extrinsic stacking faults form in (100) epitaxial silicon as the result of HF attack of the surface followed by thermal oxidation. The fault density after steam oxidation at 1100 °C is typically greater than 104 faults cm−2, whereas one or two orders of magnitude fewer faults occur during dry O2 oxidation or O2-steam-O2 oxidation following attack by HF. The fault density after steam oxidation may be reduced by etching or by anodizing the (100) epitaxial surface prior to steam oxidation. These effects may also be obtained with heat-treated (100) bulk silicon, when exposed to HF and thermally oxidized. The interpretation is that HF attacks and disorders the (100) surface, causing a fault which propagates during subsequent steam oxidation. These effects occur seldom if at all on (111) silicon. The HF-oxidation-induced faults can be the sites of microplasmas in diffused p-n junctions, and data are reported which shows that improved junctions are obtained with processing that avoids the formation of these faults.
Temperature-dependent ferroelectric domain alignment in PLZT ceramic
Authors: Salaneck William R.
Published: February 2004

The temperature dependence of the remnant dielectric polarization, PR(T), effective birefringence parameter, Δn¯(T), of hot-pressed ferroelectric 8/65/35 lead zirconate-lead titanate-lanthanum oxide (PLZT) has been investigated. The material exhibits relaxor behavior and a diffuse phase transition in the neighborhood of 102 to 109 °C. The PR(T) and Δn¯(T), however, dramatically decrease at temperatures distinctly lower than the diffuse phase transition temperature region. A ferroelectric domain alignment in poled samples, and a thermally influenced disalignment is proposed in order to account for the additional observed behavior. A mechanism based upon grain-boundary heterogeneities is suggested. Differential thermal analysis data are consistent with a domain disalignment scheme.