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Journal of Applied Physics

Issue 11 • Date Nov 1979

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Displaying Results 1 - 25 of 117
  • Theoretical analysis of liquid immersion development in electrophotography

    Page(s): 6583 - 6593
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    Liquid ink development depends upon the electrophoretic migration of charged toner particles towards a latent image, which is a pattern of surface charge on a dielectric. The electric field under which this occurs has two fundamental components—a driving field due to the latent image and an internal field which arises because of the space charge within the ink layer. A general analytic expression is obtained for the spatial frequency components of the electric field in terms of the frequency components of the charge distributions. The kinetics of the development process is then described by assuming two noninteracting species of charged particles within the ink and obtaining a solution for the motion of these particles. The problem is solved numerically for the case of a solid‐area latent image and for a periodic image. The analysis is sufficiently general so that previous results in electrophoretic development emerge as special cases, which hold within certain limitations. Guidelines are provided with regard to the importance of the space‐charge effect in a real liquid ink system. View full abstract»

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  • The effect of added hydrogen on the rf discharge chemistry of CF4, CF3H, and C2F6

    Page(s): 6594 - 6599
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    The products of 50‐W 0.5 Torr rf discharges of CF4, CF3H, C2F6, and mixtures of these gases with H2 were investigated as a function of mass‐flow rate (5–80 STD cm3/min) or H2 concentration. In addition, the C2F6 discharge was studied as a function of pressure (0.2–0.8 Torr) and power (50–200 W). Products from the CF4 discharge included F, F2, and C2F6; from CF3H: HF, CF4, C2F4, C2F6, C2HF and C2H2 were produced; from C2F6: essentially CF4 and C2F4. The addition of H2 to CF4 or C2F6 gave the same products as those from CF3H. The product distribution was a function of H2 concentration. The extent of conversion of starting material was a monotonic function of the residence time in the discharge zone. A mechanistic rationalization follows: CF4e-?F +CF3e-?F+CF2e-?F+CF. The various radicals formed underwent abstraction and recombination reactions. Addition of hydrogen altered the above equilibria as well as the nature of the discharge. View full abstract»

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  • Radiative‐transfer theory for the remote sensing of layered random media

    Page(s): 6600 - 6604
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    The radiative‐transfer theory for the remote sensing of layered media has been developed with the use of random permittivities to account for scattering effects. Analytical solutions for a three‐layer model are discussed for applications to both active and passive remote sensing. Various numerical results are illustrated to show the dependence of the brightness temperature variations on the layer thickness, the variance, the correlation length, and the permittivities. Usually the brightness temperature increases when the loss tangents increase and decreases when the variances and the correlation lengths increase. We also illustrate the case of a homogeneous layer on top of a scattering layer where the brightness temperature increases as a function of frequency and the case of only a scattering layer where brightness temperature decreases as a function of frequency. View full abstract»

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  • X‐ray spectra of beta NiAl

    Page(s): 6605 - 6608
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    The nickel L absorption spectra have been measured in equiatomic NiAl and found to agree well with the one‐electron density of states calculated by Connolly and Johnson [J.W.D. Connolly and K.H. Johnson, in Electronic Density of States, edited by L.H., Bennett, Natl. Bur. Stand. Spec. Publ. No. 323 (U.S. GPO, Washington, D.C., 1971), pp. 19–25]. Comparisons with like spectra for nickel metal show an apparent shift of the main LIII edge in NiAl, but a more critical comparison of experimental and theoretical curves shows that the 2p core holes remain equidistant from the Fermi level. This is also confirmed for the 1s core holes by remeasured Ni K spectra. The common practice of locating the Fermi level at the initial inflection point in an absorption edge, therefore, is incorrect for these spectra. Good agreement is found between x‐ray K, L, and M absorption spectra and inner‐shell emission measurements in NiAl. View full abstract»

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  • Analysis of the thermal lensing effect for an optically thick sample—A revised model

    Page(s): 6609 - 6615
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    A revised model of the thermal lensing effect is presented which treats the sample as an extended optical medium having a transverse quadratic index of refraction gradient. The revised model relaxes the restriction on sample cell length inherent in earlier models which treated the sample as an optically thin lens. It is shown how the increased sample length allows higher‐sensitivity measurement of optical absorption. Possible sources of error in the thermal lens experiment are discussed. The present model specifically addresses the problem of accounting for the elliptical beam shape of the cw dye laser used in the thermal lens experiment. The absorptivity of benzene at 607 nm (the 6←0 transition of the C‐H stretching vibration) is measured to be (2.3±0.2) ×10-3 cm-1. View full abstract»

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  • Bernstein waves in bismuth

    Page(s): 6616 - 6620
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    In this paper we have derived the general dispersion relation for electrostatic waves in bismuth in the presence of a static magnetic field along the trigonal axis by solving the Vlasov equation for electrons and holes. The effect of many‐valley band structure, anisotropy in the carrier mass, and degeneracy in the distribution function are incorporated. The dispersion relation is explicitly solved for Berstein waves. In the limit of negligible degeneracy, the dispersion relation resembles very closely to the one in gaseous plasmas. View full abstract»

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  • Experimental properties of injection lasers. VII. Narrow stripe lasers with rigid waveguide

    Page(s): 6621 - 6629
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    The properties of a type of (AlGa)As double‐heterojunction laser with buried cavity are studied as a function of current and of delay after the start of a 10‐μs square current pulse. It is found that the waveguide walls are rigid, for the mode shapes, mode dispersion, threshold, efficiency, and power‐current characteristic are independent of current and delay. The spectra are also independent of delay except for a wavelength shift from the change of temperature. The modes are tightly confined with a half‐width of 2 μm of the fundamental mode at the facet. The two lowest spatial modes dominate the emission, which is almost completely contained in one spectral doublet. The power in each member of the doublet (single‐mode power) is linear in junction voltage from less than 100 μW to the full output of 3 mW, with slope giving a critical power P*≈10 mW as in wide lasers with rigid guides. The strong doublet is transferred to successively longer wavelength modes as the current or delay is increased. The transfer suggests that a narrow gain profile is being swept past the cavity modes by a rise in temperature. View full abstract»

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  • Experimental properties of injection lasers: VIII. Narrow stripe lasers with induced waveguide

    Page(s): 6630 - 6642
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    The properties of a type of cw (AlGa)As injection laser whose waveguide is produced or modified by the conditions of operation are studied as a function of current and of delay after the start of a 10‐μs square current pulse. They are illustrated by data on a representative unit from a popular structure, the oxide stripe laser, operating in the fundamental spatial mode and with linear power‐current characteristic. At the start of the pulse the laser behaves like an oscillator with rigid cavity walls, with mode profiles invariant of current, mode powers linear in junction voltage, and smooth envelope of the spectrum. With delay, all these properties are lost; the beam changes its shape and direction, the shape and position of the coherent near field are changed, and the spectral envelope changes erratically. Since the voltage profile across the facet retains its shape and symmetry and is invariant of delay, the effects are not associated with modifications of the profile of gain or free carriers. They seem to be due to development of a temperature profile beneath the stripe contact. Comparison at fixed current between the changes with delay of the profiles of the modes and the change in propagation constant strengthens the interpretation. Analysis of this laser shows that a 15% increase in free‐carrier density is inconsequential to the observed mode confinement, and that spatial hole burning has no role in the modification of its waveguide. View full abstract»

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  • TEM observation of catastrophically degraded Ga1-xAlxAs double‐heterostructure lasers

    Page(s): 6643 - 6647
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    Defect structures of degraded GaAs/Ga1-xAlxAs double‐heterostructure (DH) lasers applied with pulsed current under high current density are studied by transmission electron microscopy. Several kinds of defects are observed corresponding to the 〈110〉 dark‐line defects which are observed in the photoluminescence patterns of the degraded DH lasers. They are arrays of dislocation tangles, nearly perfect dislocation networks, pipe‐shaped defects with strong dark contrast, and simple dislocation dipoles. The former three kinds of dislocations are assumed to be caused by the propagation of molten zone due to local heating at the mirror surface and the last defects may be caused by thermal stress. View full abstract»

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  • HCl pulsed chemical laser: An experimental study and modeling

    Page(s): 6648 - 6655
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    Two pulsed chemical HCl lasers using the reaction between H2 and Cl2 with two types of electrode structure are described. Peak power output up to 215 kW is obtained with a plane electrode configuration, and 175 kW with a helical electrode configuration. Laser action is observed on 22 vibrational‐rotational lines from H35Cl and 8 lines from H37Cl. The pulse shape and relative intensity of lasing lines obtained by using a selective cavity for the laser with helical electrode configuration are compared with computations from a model which includes kinetic processes and stimulated emission on one single line or a pair of close lines. Computed and observed results are in fair agreement for lines of (2→1) and (3→2) bands. However, for the (1→0) band the comparison suggests that an additional process occurs to populate the v=1 level. View full abstract»

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  • A helical TE N2 laser with circular beam cross section

    Page(s): 6656 - 6659
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    In this paper the operation of a helical TE N2 laser is reported which, according to its radial gain profile caused by the helical electrode geometry, produces a circular symmetric laser beam that is easily focused by ordinary spherical optics. Exhibiting a circular beam cross section together with a 20‐mm near‐field beam diameter the helical TE N2 laser generates output pulse peak powers of typically 480 kW within a pulse width (FWHM) of 5 ns. We believe the device is the first helical TE N2 laser producing output data that favorably compare with those of conventional designs. View full abstract»

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  • Scaling laws for pulsed chain‐reaction chemical lasers

    Page(s): 6660 - 6667
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    Scaling laws for pulsed chain‐reaction chemical lasers are deduced with the use of a two‐level vibrational model. The performance of a saturated laser depends only on the parameter K=tcd/tp, where tcd and tp are the characteristic collisional‐deactivation and pumping times, respectively. The normalized output energy per unit volume per pulse of a saturated HF chain‐reaction laser is 2E/ϵH2,0 =K[1+0(K)], where E is output energy per unit volume per pulse, ϵ is energy per mole of photons, and H2,0 is the initial concentration of H2 in moles per unit volume. In the range 0.02?ϕ≪1, the normalized output energy from a saturated HF laser can be expressed as 2E/ϵH2,0=ϕ, where ϕ∼ (F/F2)1/20(F2/H2)0[1 +0.094(F2/H2)0]-1/2. In the latter regime the product Ete is a constant for a saturated laser (te=pulse length). View full abstract»

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  • Acceleration of the gradual degradation in (GaAl)As double‐heterostructure lasers as an exponent of the value of the driving current

    Page(s): 6668 - 6674
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    Double‐heterostructure (GaAl)As lasers are tested at various temperatures and driving conditions, including spontaneous mode operation. Results show that the rate of degradation is primarily determined by driving current rather than optical output when aging at optical outputs of 10 mW/facet or less and heat‐sink temperatures of 50–100 °C. A new composite Arrhenius relation including a current‐dependent factor is empirically derived, and excellent agreement is found between calculated and experimental results, especially in regard to the effects of current on the rate of gradual degradation. The thermal activation energy derived by the above relation is estimated to be 0.8±0.1 eV, and laser lifetime at an optical output of 5 mW/facet and heat‐sink temperature of 25 °C is expected to exceed 3.4×105 h. The role of current in inducing gradual degradation is also discussed. View full abstract»

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  • Characteristics of rib waveguides in AlGaAs

    Page(s): 6675 - 6687
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    We have studied the properties of isolated and coupled optical rib waveguides (RWG) as a function of rib height and width in GaAs layers on AlGaAs for TE‐like and TM‐like polarizations. We compare mode shape parameters for isolated RWG to the coupling constant, K, obtained from distributed couplers. The effective index model accurately describes the mode distributions and the coupling constant for single‐mode RWG. The model also gives an accurate estimate for anodic oxide loaded strip waveguides. In this model, the relative lateral difference in the effective dielectric constant, Δx, is determined by the depth characteristics (the rib height, layer thicknesses, and compositions) and the free‐space wavelength. The lateral confinement of guided modes and K are then determined by Δx, the effective dielectric constant, the waveguide width, the waveguide spacing, and the free‐space wavelength. At λ?1.06 μm, ribs of height h?0.05 μm on GaAs waveguiding layers of thickness t?0.75 μm with underlying Al0.1Ga0.9As cladding provide Δx?1.7×10-3 for TE polarization and ?2×10-3 for TM polarization. In such layers K?1/mm for pairs of RWG with 3 μm width and 3 μm spacing. Model Δx results are given for typical layer compositions and typical layer and rib dimensions. Eigensolution results for K are given as a function of Δx for typical rib width and spacing dimensions. For more general application to RWG, to anodic loaded strip guides, and to metal gap guides, scaled K and linearized Δx results are given in dimensionless form. We also report experiments on lateral tapers to widen or narrow the waveguides for control of mode shapes, and on lateral ramps to control the location of the RWG. Tapers introduce negligible loss, but cause some mode - conversion if multimoded guides are involved. Ramps introduce negligible loss if they are at sufficiently low angles. View full abstract»

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  • Mode coupling between slab‐type optical waveguides via dichroic absorption of M centers

    Page(s): 6688 - 6690
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    Guided wave coupling in slab‐type optical waveguides covered with an NaF crystal containing oriented M centers is analyzed with the complex propagation constant. In this treatment the complex coupling coefficient is also introduced. An additional experiment supports this analysis. This conception is useful in designing optical waveguide functional devices. View full abstract»

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  • A large‐aperture electro‐optic diffraction modulator

    Page(s): 6691 - 6693
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    Efficient modulation of a large‐diameter light beam based on diffraction by an electro‐optic phase grating has been demonstrated. The modulator consists of a y‐cut lithium niobate crystal with interdigital electrodes on one surface. With a polarized HeNe laser beam incident normal to the surface, an extinction ratio of 100 : 1 was obtained for the zeroth‐order transmitted beam at an applied voltage of 1650 V for single‐pass transmission. This device has been used to modulate a retroreflected beam in an optical communications experiment, with good performance for aperture areas greater than 15 cm2 and incidence angles up to 30°. View full abstract»

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  • Thin‐film optical waveguide polarizer using semiconducting cadmium sulphide

    Page(s): 6694 - 6696
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    An optical waveguide attenuative polarizer is realized by a slab‐type glass film waveguide covered with a semiconducting cadmium sulphide top layer. Cross‐sectional energy distribution and absorption in the guide is vitally influenced by the top layer thickness for each polarization mode. Selection of the specific mode can be achieved by controlling the top layer thickness. Experiment is compared with theoretical analysis. View full abstract»

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  • Power flow and energy distribution of magnetostatic bulk waves—In dielectric‐layered structure

    Page(s): 6697 - 6699
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    This paper presents a theoretical investigation of guided propagation of the magnetostatic bulk waves in a normally magnetized ferrite film separated from a perfect conductor by a dielectric layer. Starting from the generalized Poynting theorem for dispersive media, the expressions for time‐averaged power flow and energy density have been obtained in the magnetostatic approximation. The velocity of time‐averaged energy flow has been shown to be equal to the group velocity, which establishes the consistency of magnetostatic approximation from the energy point of view. View full abstract»

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  • Self‐sustained oscillations in (AlGa)As oxide‐defined stripe lasers

    Page(s): 6700 - 6706
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    Experimental results are presented for the incidence statistics and physical characteristics of self‐sustained oscillations in the output of (AlGa)As oxide‐defined stripe lasers. Oscillations near threshold are found to be associated with aging but not necessarily to output degradation. The morphology, frequency relationship with current and time resolved near‐field characteristics are presented. These observations are consistent with a rate equation model incorporating saturable absorption. Implications of this model to laser stability are discussed. View full abstract»

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  • Laser performance of a glass‐clad LiNdP4O12 rectangular waveguide

    Page(s): 6707 - 6712
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    A LiNdP4O12 rectangular waveguide clad by sputtered SK5 glass was fabricated. Quasi‐cw laser operations at 1.048 and 1.317 μm were obtained both in an Ey00 single‐transverse mode, by argon‐laser coaxial pumping (0.5145 μm). The round‐trip cavity losses were evaluated to be 14.3% (1.05 μm) and 6.5% (1.32 μm). Waveguide‐mode calculation, observed laser‐characteristics analysis, and transverse‐pumping estimation are also described. View full abstract»

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  • Explosive puncturing of metal plates by lasers

    Page(s): 6713 - 6718
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    Substantial energy savings in puncturing metal plates by laser radiation can be achieved by heating the metal by cw radiation to a temperature closely below the melting point and then applying a sharp radiation pulse to push the hot metal plug through the plate. An analysis of this process is presented, in which the non‐Newtonian viscosity behavior of metals is considered. Scale‐up effects and efficiency calculations are presented for laser‐supported detonation waves and point explosions. Flow characteristics as well as penetration criteria are given for aluminum, copper, and steel which are in good agreement with experimental data. View full abstract»

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  • Surface‐wave reflection phenomena at interfaces on y‐z LiNbO3

    Page(s): 6719 - 6728
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    Light‐scattering techniques were used to study various aspects of the reflection of surface acoustic waves (SAW) at three different interfaces on y‐z LiNbO3. Investigated were a free‐metallized surface boundary, the edge of a thick gold film, and a crystal corner. In all three cases, the reflection coefficient was measured and found to be a maximum for the crystal corner and small for both film interfaces. Light scattering from the acoustically created surface corrugations near the interface was used to identify the transition region in which bulk modes as well as SAW are present. The angular spectrum and total power of bulk waves created via mode conversion from surface waves were also measured. View full abstract»

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  • Acousto‐optic measurement of bulk wave generation by interdigital transducers excited at SAW resonance

    Page(s): 6729 - 6732
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    The angular distribution and total power of bulk acoustic waves generated by one and 25 finger pair interdigital transducers on y‐z lithium niobate are reported. It was found that the bulk wave radiation from the 25 finger pair grid originates primarily from the transducer ends. View full abstract»

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  • Resolution criteria in scanning microscopes

    Page(s): 6733 - 6736
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    The physical nature of the sample‐illuminating wave (coherent or incoherent and focused or plane) and of the detector (phase or intensity sensitive) must be accounted for in the definition of a resolution criterion for a scanning microscope. The purpose of this paper is to study the resolution criterion for coherent scanning acoustical and optical microscopes, owing to the properties of the available detectors for each kind of radiation. The theoretical results are well supported by the experimental findings for the scanning acoustic microscope. View full abstract»

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  • Acoustic harmonic generation due to fatigue damage in high‐strength aluminum

    Page(s): 6737 - 6741
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    It is shown that acoustic second harmonic generation is a useful tool for studying surface microcrack development during fatigue of a high‐strength aluminum alloy. A fundamental (5 MHz) surface acoustic wave (SAW) was transmitted across the gauge section of flexural fatigue specimens of Al 7075‐T6. The second harmonic amplitude was determined after several increments of fatigue, as a function of external load and the amplitude of the fundamental. It was found that the second harmonic signal is at a maximum close to zero external load and increases with progressing fatigue. Harmonic generation, attributable to microcracking at the surface, has been observed as early as 10–20% of the expended fatigue life. A simple analysis to obtain a coefficient of harmonic‐generation efficiency versus applied surface stress is described. This analysis considers the effect of changes in attenuation of the fundamental and harmonic waves associated with degree of surface microcrack opening as a function of surface stress. It is shown that acoustic harmonic generation may be a useful tool for reliable monitoring of the state of fatigue of a structural material. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory