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1 Sep 1998

Volume 84, Issue 5, pp. 2371-2982

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Logistic function and evolution of free-electron-laser oscillators

G. Dattoli

J. Appl. Phys. 84, 2393 (1998); http://dx.doi.org/10.1063/1.368365 (6 pages) | Cited 5 times

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In this article we show that the logistic function can be exploited to describe the evolution of free-electron-laser oscillators with the inclusion of lethargy, cavity tuning effects, etc. It is also proved that it offers a useful tool to gain a deeper understanding of the time dependence on the spectral features of the optical packet. © 1998 American Institute of Physics.
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41.60.Cr Free-electron lasers
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Photonic band gaps in metallic microcavities

S. C. Kitson, W. L. Barnes, and J. R. Sambles

J. Appl. Phys. 84, 2399 (1998); http://dx.doi.org/10.1063/1.368366 (5 pages) | Cited 14 times

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We investigate the mode structure of optical microcavities made using metallic mirrors. By giving one of the mirrors wavelength scale periodic texture we show that cavity modes, in particular the antisymmetric coupled surface plasmon polariton mode, may be blocked by a photonic band gap. We compare experimental and theoretical results and use them to indicate how changing the type of texturing may be used to control the modes of the microcavity. The relevance of the reported work to microcavity devices such as the light emitting diode is also discussed. © 1998 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
85.60.Jb Light-emitting devices

Interaction of laser-generated surface acoustic pulses with fine particles: Surface cleaning and adhesion studies

Al. A. Kolomenskii, H. A. Schuessler, V. G. Mikhalevich, and A. A. Maznev

J. Appl. Phys. 84, 2404 (1998); http://dx.doi.org/10.1063/1.368367 (7 pages) | Cited 16 times

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The mechanical forces associated with the surface acceleration in high-amplitude surface acoustic waves (SAWs) detach the particles from the surface. The removal of micron sized particles with a nanosecond SAW pulse excited by a focused laser beam in a silicon wafer was quantitatively investigated. Both vertical and horizontal particle displacements have been observed. It is shown that for nanosecond SAW pulses the limit of the surface acceleration of about 1010 m/s2 is set by the fracture of the material and corresponds to the removal of particles larger than about 0.05 μm. In addition, the nonlinear transformation of the excited SAW pulses results in an increase of the surface acceleration and contributes to the cleaning process extending it to even smaller particle dimensions. The technique is applicable in vacuum and improves the energetic effectiveness of the cleaning due to the removal of particles not only in the irradiated region, but also in the wider area covered by the SAW pulse propagation. It can be also used for the determination of the Hamaker constant of the adhesion force. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
68.35.Gy Mechanical properties; surface strains
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
62.65.+k Acoustical properties of solids

Optical and x-ray characterization of HxLi1−xNbO3 phases in proton-exchanged LiNbO3 optical waveguides

Yu. N. Korkishko, V. A. Fedorov, and S. M. Kostritskii

J. Appl. Phys. 84, 2411 (1998); http://dx.doi.org/10.1063/1.368437 (9 pages) | Cited 13 times

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Infrared reflection, attenuated total reflection, prism coupling, and x-ray diffraction methods were used to characterize seven crystallographic HxLi1−xNbO3 phases in proton-exchanged Z-cut LiNbO3 waveguides. Drastic changes of the crystal lattice parameters and the lattice vibrational spectrum at the phase boundaries were observed. The LO–TO splitting, which is proportional to the width of the main band ranging from 580 to 900 cm−1, was demonstrated to vary significantly from phase to phase. Strong decrease of the LO–TO splitting for the polar mode attributed to NbO6 octahedra vibrations (800–900 cm−1) was detected. It was shown that the HxLi1−xNbO3 phases are organized as individual layers. © 1998 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.70.-a Optical materials
78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices

Photostimulated impurity absorption of ultrasound in semiconductor nanostructures

O. A. C. Nunes, Q. Fanyao, W. Santos, A. L. Fonseca, and D. Agrello

J. Appl. Phys. 84, 2420 (1998); http://dx.doi.org/10.1063/1.368368 (6 pages) | Cited 1 time

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The problem of attenuation of ultrasound in a semiconductor with a quantum well structure with infinite potential barriers is tackled for the case in which the acoustic lattice vibrations interact with impurity centers in the presence of an exciting laser field. The electron transitions from an acceptor-impurity “band” to the first quantized energy level of the conduction band, forbidden in the absence of the laser field for the absorption of an acoustic wave quantum, become permitted in the presence of the external high frequency field. The external laser field will then supply the energy deficit for the electron to make the transition to absorb the acoustic phonon. The total ultrasound absorption coefficient αT was calculated using second-order perturbation theory and the result was specialized for the case of a GaAs/AlGaAs quantum well sample. It was found that αT is a fairly large quantity as compared with its value in bulk as the well width decreases from values corresponding to the almost bulk situation. © 1998 American Institute of Physics.
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62.65.+k Acoustical properties of solids
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
63.20.kp Phonon-defect interactions

Plasma chemistry aspects of a-Si:H deposition using an expanding thermal plasma

M. C. M. van de Sanden, R. J. Severens, W. M. M. Kessels, R. F. G. Meulenbroeks, and D. C. Schram

J. Appl. Phys. 84, 2426 (1998); http://dx.doi.org/10.1063/1.368977 (10 pages) | Cited 71 times

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The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl (SiH3) radical whereas the ion-electron induced dissociation mechanism leads to SiHx (x<3) radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals SiHx(x<3) with silane. Almost independent of the plasma conditions used, approximately one H2 is produced per consumedSiH4 molecule. Disilane production is observed which roughly scales with the remaining silane density. Possible production mechanisms for both observations are discussed. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology

Influence of ionic composition of water on the corona discharge around water drops

M. Škarja, M. Berden, and I. Jerman

J. Appl. Phys. 84, 2436 (1998); http://dx.doi.org/10.1063/1.368369 (7 pages) | Cited 8 times

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We performed a series of experiments to investigate the influence of different salts dissolved in water on the corona discharge patterns around water drops and on subsequent image formation. Considering our research needs, we developed a special method of corona discharge electrography of water drops with computer analysis of images. Our method differs from the usual corona discharge photography (known also as Kirlian photography) in the mechanisms of image formation. It relies on chemical reactions and deposition of substances transported in the discharge area rather than on the usual photoreactions. Higher reproducibility of results is achieved through simultaneous imaging and comparing two drops from different samples. In the presented experiments we compare different salt solutions with distilled water and between themselves. Results show distinct behavior of corona discharge patterns as regards ionic composition of salts, both radially and angularly. The present investigation may also shed some light on the problem of the influence of a different ionic composition in using this type of method for diagnostic purposes. © 1998 American Institute of Physics.
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52.80.Hc Glow; corona

Solution of the radiative transfer equation in an absorbing and scattering Nd:YAG laser-induced plume

D. Lacroix, G. Jeandel, and C. Boudot

J. Appl. Phys. 84, 2443 (1998); http://dx.doi.org/10.1063/1.368405 (7 pages) | Cited 8 times

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We analyze the scattering effect in a laser-induced plasma plume in the case of a Nd:YAG laser welding process using a discrete ordinate scheme and the radiative transfer equation. The optical properties of plume vapors from stainless steel are analyzed at various temperatures as different parameters are varied (laser wavelength, plasma pressure and composition, type of shielding gas). The scattering coefficients and the phase function due to the presence of small particles in the plume are calculated using the Mie theory for different particle diameters and several densities of particles in the medium. With our model we estimate the temperature in the plasma plume. © 1998 American Institute of Physics.
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44.40.+a Thermal radiation
79.20.Ds Laser-beam impact phenomena
81.65.-b Surface treatments

Determination of negative-ion and electron parameters in an Ar/SF6 plasma

E. Stamate and K. Ohe

J. Appl. Phys. 84, 2450 (1998); http://dx.doi.org/10.1063/1.368406 (9 pages) | Cited 32 times

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A new method for evaluating negative ion and electron parameters from the current–voltage characteristics of electric probes is presented. A theoretical model and its related numerical procedures are established and errors included are estimated. Temperatures and densities of negative ions and electrons in a magnetic multipolar-confined plasma of Ar and Ar/SF6 mixtures are determined with allowable errors for various density ratios of the negative ion to the electron. © 1998 American Institute of Physics.
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52.25.Kn Thermodynamics of plasmas
52.70.Ds Electric and magnetic measurements
52.27.Jt Nonneutral plasmas
52.55.-s Magnetic confinement and equilibrium
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