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15 Jan 1999

Volume 85, Issue 2, pp. 641-1243

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Capture radius of magnetic particles in random cylindrical matrices in high gradient magnetic separation

Mayuree Natenapit and Wirat Sanglek

J. Appl. Phys. 85, 660 (1999); http://dx.doi.org/10.1063/1.369199 (5 pages) | Cited 7 times

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An effective medium treatment (EMT) was used to model the magnetic field around randomly distributed magnetic cylindrical fine wires and applied to calculate the capture radius of paramagnetic particles in a filter operating either in the longitudinal or transverse design mode. This article reports capture radius as a function of the ratio of magnetic velocity to fluid entrance velocity with a magnetic parameter which determines the strength of the magnetic short-range force, as a parameter. Finally, comparisons of the results based on the EMT approach, with those obtained by using the single-wire model, are given along with discussion on the criteria for validity of the simple single-wire model. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
85.70.-w Magnetic devices
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
07.55.-w Magnetic instruments and components
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Relaxation kinetics in quantum cascade lasers

S. Slivken, V. I. Litvinov, M. Razeghi, and J. R. Meyer

J. Appl. Phys. 85, 665 (1999); http://dx.doi.org/10.1063/1.369200 (7 pages) | Cited 11 times

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Relaxation kinetics in a quantum cascade intersubband laser are investigated. Distribution functions and gain spectra of a three-subband double-quantum-well active region are obtained as a function of temperature and injection current. The potentially important role of the nonequilibrium phonons at lasing threshold is shown and discussed in details. It is shown that the threshold current is strongly dependent of the power dissipated in the active region in steady state. The numerical calculations for an 8.5 μm laser illustrate the general issues of relaxation kinetics in quantum cascade lasers. Temperature dependence of the threshold current is obtained in a good agreement with the experiments. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

J. Y. Lin, G. J. Tallents, R. Smith, A. G. MacPhee, E. Wolfrum, J. Zhang, G. Eker, R. Keenan, C. L. S. Lewis, D. Neely, R. M. N. O’Rourke, G. J. Pert, S. J. Pestehe, and J. S. Wark

J. Appl. Phys. 85, 672 (1999); http://dx.doi.org/10.1063/1.369201 (4 pages) | Cited 11 times

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We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Å, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. © 1999 American Institute of Physics.
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42.55.Vc X- and γ-ray lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Higher-order optical nonlinearity observed in host–guest liquid crystals

Hiroshi Ono and Yoshiro Harato

J. Appl. Phys. 85, 676 (1999); http://dx.doi.org/10.1063/1.369202 (5 pages) | Cited 11 times

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Optical nonlinearity in host–guest liquid crystals was characterized by systematically investigating both the experimental diffraction beam pattern and the theoretical one originating in photothermal self-phase modulation. The experimental diffraction patterns were in very good agreement with the calculated results when the refractive index changes (Δn) were assumed to be described by the equation Δn = n2I+n4I2, where n2 and n4 are nonlinear coefficients, and I is the light intensity. These higher-order nonlinear coefficients were strongly dependent on the nematic–isotropic transition temperatures of the host–guest liquid crystals, dye concentration, and sample thickness. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals

Comparison of the temperature dependence of optical poling between guest-host and side-chain polymer films

Gang Xu, Jinhai Si, Xuchun Liu, Q. G. Yang, Peixian Ye, Zhao Li, and Yuquan Shen

J. Appl. Phys. 85, 681 (1999); http://dx.doi.org/10.1063/1.369147 (5 pages) | Cited 14 times

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A comparison of temperature-dependent optical poling between two azopolymers, a side-chain polymer system (disperse red 19-functionalized polyimide polymer) and a guest-host polymer (dispersed red 1-doped polymethyl methacrylate), has been performed at various poling temperatures ranging from 25 to 70 °C. The observed saturation levels of induced second-order nonlinear susceptibility in all cases could be resolved into two components with a faster and a slower decay process after poling, which were respectively attributed to the cis-to-trans isomerization and the loss of induced polar order by orientational diffusion of azo chromophores. The saturation level and its slower decay component were observed to increase with the increase of poling temperature in the side-chain polymer, but to decrease in the guest-host system. The faster decay components were observed to decrease with poling temperature in both the systems. The decay times of the faster component decreased with temperature in the two polymers. The decay times of the slower component in the guest-host polymer, which were much smaller than those in the side-chain polymer, also decreased with temperature. All the observations have been explained physically. © 1999 American Institute of Physics.
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77.22.Ej Polarization and depolarization
42.65.An Optical susceptibility, hyperpolarizability
77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
78.66.Qn Polymers; organic compounds

Observation of downstream energetic electron/ion flow and accompanied high-power microwave radiation during the opening of a submicrosecond plasma opening switch

Ya. E. Krasik, A. Dunaevsky, J. Felsteiner, and J. R. Goyer

J. Appl. Phys. 85, 686 (1999); http://dx.doi.org/10.1063/1.369148 (10 pages) | Cited 3 times

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In this article, results of experimental investigations of high-energy electron beam generation and transportation in the region downstream of a submicrosecond plasma opening switch (POS) (Ipos  ⩽ 35 kA, τ1/4 ≅ 300 ns) are presented. This electron beam is accompanied by collectively accelerated ions having energies several times higher than the electron energies. Experiments were carried out with different loads: short-circuit, high-impedance, and planar electron diode. It is shown that the electron/ion beam appearance in the region downstream of the POS load occurs almost simultaneously with the beginning of the inductive voltage, independently of the type of load. In addition, generation of high-power microwave radiation (fmw  ⩽ 10 GHz, Pmw ⩽ 200 MW) was observed for all types of loads. We believe that the generation of the microwave radiation is related to the injection of a noncomplete charge-neutralized electron beam into the downstream drift region. These results and a qualitative explanation of the generation of the inductive voltage and microwave radiation are discussed. © 1999 American Institute of Physics.
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52.75.Kq Plasma switches (e.g., spark gaps)
07.77.Ka Charged-particle beam sources and detectors
29.25.Bx Electron sources
41.75.Fr Electron and positron beams

Absolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging

L. Chérigier, U. Czarnetzki, D. Luggenhölscher, V. Schulz-von der Gathen, and H. F. Döbele

J. Appl. Phys. 85, 696 (1999); http://dx.doi.org/10.1063/1.369149 (7 pages) | Cited 24 times

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Absolute atomic hydrogen densities were measured in the gaseous electronics conference reference cell parallel plate reactor by Doppler-free two-photon absorption laser induced fluorescence spectroscopy (TALIF) at λ=205 nm. The capacitively coupled radio frequency discharge was operated at 13.56 MHz in pure hydrogen under various input power and pressure conditions. The Doppler-free excitation technique with an unfocused laser beam together with imaging the fluorescence radiation by an intensified charge coupled device camera allows instantaneous spatial resolution along the radial direction. Absolute density calibration is obtained with the aid of a flow tube reactor and titration with NO2. The influence of spatial intensity inhomogenities along the laser beam and subsequent fluorescence are corrected by TALIF in xenon. A full mapping of the absolute density distribution between the electrodes was obtained. The detection limit for atomic hydrogen amounts to about 2×1018 m−3. The dissociation degree is of the order of a few percent. © 1999 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.Pi High-frequency and RF discharges

Experimental setup and electrical characteristics of an inductively coupled plasma

V. A. Godyak, R. B. Piejak, and B. M. Alexandrovich

J. Appl. Phys. 85, 703 (1999); http://dx.doi.org/10.1063/1.369150 (10 pages) | Cited 38 times

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This article describes an experimental system that has been used to study inductively coupled plasma (ICP). The aim of this effort was to generate an experimental ICP database over a wide range of discharge conditions (power, frequency, and gas pressure) obtained in the same experimental device and using the same diagnostic means. Design of the experimental setup and diagnostics for measurement of ICP external electrical characteristics (coil voltage and current), power dissipated in plasma and radio frequency plasma potential are given here together with experimental results obtained over a wide range of discharge conditions. © 1999 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges

Characterization and modeling of the ablation plumes formed by intense-pulsed ion beam impact on solid targets

H. A. Davis, G. P. Johnston, J. C. Olson, D. J. Rej, W. J. Waganaar, C. L. Ruiz, F. A. Schmidlapp, and M. O. Thompson

J. Appl. Phys. 85, 713 (1999); http://dx.doi.org/10.1063/1.369151 (9 pages) | Cited 4 times

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An investigation of the properties of the ablation products from intense-pulsed ion beam impact on solid targets is described. Measurements and calculations of the properties of the ablation plume are presented and correlated with incident beam parameters. Experimental techniques include Thomson parabola particle spectroscopy to measure the incident ion beam atomic composition and the energy spectrum of each beam component, thermal imaging to measure the incident-beam energy density, time-resolved photography to measure the plume expansion time history and geometry, and time-resolved energy-density measurements of the plume. The results of a thermal transport model of the beam-target interaction are presented, and a detailed comparison with measurements is made. © 1999 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.50.Dg Plasma sources
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
41.85.Ja Particle beam transport
41.75.Ak Positive-ion beams
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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