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15 Aug 2006

Volume 100, Issue 4, Articles (04xxxx)

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Constructal theory of generation of configuration in nature and engineering

Adrian Bejan and Sylvie Lorente

J. Appl. Phys. 100, 041301 (2006); http://dx.doi.org/10.1063/1.2221896 (27 pages) | Cited 122 times

Online Publication Date: 29 August 2006

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Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997) ]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.
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47.85.-g Applied fluid mechanics
47.10.-g General theory in fluid dynamics
47.27.-i Turbulent flows
47.55.D- Drops and bubbles
87.19.rs Movement
87.19.ru Locomotion
01.30.Rr Surveys and tutorial papers; resource letters
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Doping in quantum cascade lasers. I. InAlAs–InGaAs/InP midinfrared devices

Thierry Aellen, Mattias Beck, Nicolas Hoyler, Marcella Giovannini, Jérôme Faist, and Emilio Gini

J. Appl. Phys. 100, 043101 (2006); http://dx.doi.org/10.1063/1.2234804 (4 pages) | Cited 15 times

Online Publication Date: 17 August 2006

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The effect of the doping densities on the performance of 9 μm InAlAs–InGaAs/InP quantum cascade lasers is presented. Doping densities varying between 1.0×1011 and 2.6×1011 cm−2 were investigated. In this range, a linear increase in both threshold and maximum current density with sheet carrier density is observed. These effects are explained using a model based on resonant tunneling transport and rate equations.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors

Doping in quantum cascade lasers. II. GaAs/Al0.15Ga0.85As terahertz devices

Lassaad Ajili, Giacomo Scalari, Marcella Giovannini, Nicolas Hoyler, and Jérôme Faist

J. Appl. Phys. 100, 043102 (2006); http://dx.doi.org/10.1063/1.2234805 (3 pages) | Cited 16 times

Online Publication Date: 17 August 2006

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The performances of GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers based on a bound-to-continuum transition are investigated as a function of injector doping. A linear dependence between threshold current and doping is found and agrees with the expected increase of waveguide losses due to free carrier absorption.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals

Influence of the average molecular weight and the concentration of plasticizer on the orientational dynamics of chromophores in guest-host polymers

J. C. Ribierre, L. Mager, F. Gillot, A. Fort, and S. Méry

J. Appl. Phys. 100, 043103 (2006); http://dx.doi.org/10.1063/1.2234811 (9 pages) | Cited 2 times

Online Publication Date: 17 August 2006

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We report experimental results obtained from dielectric spectroscopy, electro-optic, and second harmonic generation dynamics measurements on different polymers doped with nonlinear optical chromophores. The polymers considered in this work are polyvinylcarbazole plasticized by ethylcarbazole and polystyrenes with different average molecular weights. Altogether the influence of temperature, average molecular weight of the polymer host, and concentration of plasticizer on the orientational processes of chromophores is investigated and described by polymer rheology laws. Finally, these results, which identify the major role played by the average molecular weight of polymers on the orientational dynamics of chromophores, suggest another possible way of optimization for low glass transition temperature photorefractive polymers, where fast orientational response times are required.
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42.70.Jk Polymers and organics
82.35.Ej Nonlinear optics with polymers
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
36.20.Cw Molecular weights, dispersity
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Long-range surface plasmon-polariton mode cutoff and radiation in embedded strip waveguides

Ian Breukelaar, Robert Charbonneau, and Pierre Berini

J. Appl. Phys. 100, 043104 (2006); http://dx.doi.org/10.1063/1.2244479 (9 pages) | Cited 25 times

Online Publication Date: 18 August 2006

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Using a fully vectorial formulation, the normal mode analysis method is used to model the radiative spreading of surface plasmon-polariton mode input into regions where the bound surface mode is cut off or radiative. The analysis was performed at λ0 = 1.55 μm for embedded finite width strip metal waveguides, where the metal was Au and the surrounding dielectrics were SiO2 and LiNbO3. Mode cutoff is induced by an asymmetry between the index of refraction of the top clad and the bottom clad. Comparisons between predictions and experimental results show very good agreement. The analysis was performed for a range of waveguide dimensions, and results show that a change in insertion loss of better than 20 dB is possible for an appropriate waveguide and dielectric asymmetry. Practical applications to make use of this cutoff effect are outlined.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Influence of geometric shape of optically trapped particles on the optical rotation induced by vortex beams

S. H. Tao, X.-C. Yuan, J. Lin, and Y. Y. Sun

J. Appl. Phys. 100, 043105 (2006); http://dx.doi.org/10.1063/1.2260823 (5 pages) | Cited 1 time

Online Publication Date: 18 August 2006

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Particles optically trapped and rotated in fluidic medium by a vortex beam receive a torque exerted by orbital angular momentum of the beam. Size and shape of the trapped particles are found to affect the rotation remarkably; e.g., a lump of particles is easier to be set in rotation than a single particle, and a row of particles stuck to each other will rotate faster than isolated particles. Influences of the size and arranging manner of a group of particles on the rotation are investigated analytically and experimentally.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.25.Ja Polarization

On a thermally induced readout mechanism in super-resolution optical disks

Masashi Kuwahara, Takayuki Shima, Paul Fons, Toshio Fukaya, and Junji Tominaga

J. Appl. Phys. 100, 043106 (2006); http://dx.doi.org/10.1063/1.2227643 (6 pages) | Cited 16 times

Online Publication Date: 18 August 2006

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We have simultaneously measured the carrier-to-noise ratio (CNR) as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure (PtOx super-RENS) disks. The the reflected and transmitted light intensities were found to decrease and increase, respectively, as the CNR value increased. The phase-change material AgInSbTe (AIST) used in PtOx super-RENS disks was found to exhibit a strong optical nonlinearity with respect to readout laser power. AIST becomes transparent at higher laser powers. To ascertain whether the presence of Pt nanoparticles is important to the readout mechanism, a super-RENS disk was fabricated in which the PtOx layer was replaced with a metal-free phthalocyanine (H2Pc) layer and the CNR of the H2Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtOx, we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, we also investigated the use of Si and the alloy Ge2Sb2Te5 in lieu of AIST in a super-RENS disk and simple three layer structure disks. The super-resolution effect was observed for all disk types. Based upon these observations, we discuss the possibility of a thermal origin for the super-resolution effect in all super-resolution disks.
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42.79.Vb Optical storage systems, optical disks
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics

Optoelectronic switches based on diffusive conduction

Hilmi Volkan Demir, Fatih Hakan Koklu, Micah B. Yairi, James S. Harris, and David A. B. Miller

J. Appl. Phys. 100, 043107 (2006); http://dx.doi.org/10.1063/1.2234818 (7 pages)

Online Publication Date: 18 August 2006

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We study the process of diffusive conduction that we use in our optoelectronic switches to achieve rapid optical switching (on a picosecond time scale). We present the characteristic Green’s function of the diffusive conduction derived for arbitrary initial conditions. We also report the series solutions of the diffusive conduction obtained for different boundary conditions (V = 0 and ∇V = 0 along the device contact lines) in different device geometries (rectangular and circular mesas). Using these analytical results, we investigate the effect of boundary conditions on the switching operation and the steady state behavior in optical links. We demonstrate the feasibility of using such diffusive conductive optoelectronic switches to establish optical links in return-to-zero and non-return-to-zero coding schemes. For multichannel optical switching, we discuss possible use of a single optoelectronic switch to accommodate multiple channels at once, with >100 optical channels (with a 2000 mm−2 channel density and <10% cross-talk), predicted on a 300×300 μm2 mesa with a device switching bandwidth of >50 GHz, leading to a 5 Tb/s aggregate transmission in principle. This approach of using multiple parallel channels on a single switch is completely opposite to the traditional idea of arraying many switches. This proposed scheme eliminates the need for on-chip switch integration and the need for the alignment of the optical channels to the integrated individual switches.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Modeling the crystal-field splitting of energy levels of Er3+(4f11) in charge-compensated sites of KPb2Cl5

John B. Gruber, Raylon M. Yow, Anmol S. Nijjar, Charles C. Russell, Dhiraj K. Sardar, Bahram Zandi, Arnold Burger, and Utpal N. Roy

J. Appl. Phys. 100, 043108 (2006); http://dx.doi.org/10.1063/1.2244416 (6 pages) | Cited 9 times

Online Publication Date: 22 August 2006

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A point-charge lattice-sum model corrected for induced multipoles is used to investigate the crystal-field splitting of the math energy levels of Er3+(4f11) ions that occupy charge-compensated sites in the laser host crystal KPb2Cl5. Spectroscopic data are reported and analyzed for Er3+ between 1550 and 440 nm at cryogenic temperatures. The crystal-field (Stark) splitting of the ground-state manifold math and the splitting of individual excited manifolds of Er3+ are established from analyses of temperature-dependent (hot band) absorption spectra. The analyses confirm the Stark splitting of the math and math manifolds that are reported in the literature. From an analysis of the data, it appears that only one of the two possible Pb2+ sites serving as a charge-compensated site for Er3+ is involved in the optical activity of the Er3+ ions. From an examination of the crystallographic data of KPb2Cl5, we identify a possible site for the optically active Er3+ ion in the lattice and calculate the lattice-sum components for that site. These components are used to evaluate the crystal-field splitting of the energy levels of Er3+ at that site. The charge-compensation model assumes that Er3+ substitutes for Pb2+ in the Pb(2) site with a vacancy in a nearby K+ site. To obtain the best overall agreement between calculated and experimental levels, the position of the Er3+ ion is treated as an adjustable parameter along the quantization axis. Individual manifold centroids of the Er3+ ion are also varied. From a least-squares fitting analysis, we obtain a rms deviation of 10 cm−1 between 48 calculated-to-observed Stark levels.
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42.70.-a Optical materials
71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
78.20.Ek Optical activity

Thermal modeling of GaInAs/AlInAs quantum cascade lasers

Antonia Lops, Vincenzo Spagnolo, and Gaetano Scamarcio

J. Appl. Phys. 100, 043109 (2006); http://dx.doi.org/10.1063/1.2222074 (5 pages) | Cited 25 times

Online Publication Date: 22 August 2006

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We measured the facet temperature profiles of GaInAs/AlInAs quantum cascade lasers (QCLs) operating in continuous wave mode by means of microprobe photoluminescence. These results were used to evaluate the in-plane (k‖) and the cross-plane (k⊥) thermal conductivities of the active region and to validate a two-dimensional model for the anisotropic heat diffusion in QCLs. In the temperature range of 80–250 K, k⊥ monotonically increases with temperature and remains one order of magnitude smaller than the thermal conductivities of bulk constituent materials. We found an excellent agreement between the calculated and experimental values of the thermal resistance of GaInAs/AlInAs QCLs operating in continuous wave up to 400 K. Comparison between the calculated thermal performances of QCLs sharing the same active region structure, but having either a buried or a ridge waveguide, shows that devices with Au contact layers thicker than 4 μm have better thermal properties than the buried structures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Analysis of second harmonic generation in photonic-crystal-assisted waveguides

Antonella D’Orazio, Domenico de Ceglia, Marco De Sario, Francesco Prudenzano, Mark J. Bloemer, and Michael Scalora

J. Appl. Phys. 100, 043110 (2006); http://dx.doi.org/10.1063/1.2266104 (5 pages) | Cited 3 times

Online Publication Date: 22 August 2006

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We study second harmonic generation in a planar dielectric waveguide having a low-index, polymer core layer, bounded by two multilayer stacks. This geometry allows exceptionally strong confinement of the light at the fundamental wavelength inside the core region with virtually zero net propagation losses for distances that exceed several centimeters, provided that material and scattering losses are neglected. A phase-matched configuration of the waveguide is reported in which the pump signal is the lowest-order mode of the waveguide, and the generated second harmonic signal corresponds to the third propagation mode of the waveguide. Using a polymer waveguide core, having χ(2) ∼ 100 pm/V, we predict a conversion efficiency of approximately 90% after a propagation distance of 2 mm, using peak pump intensities inside the core of the waveguide of 1.35 GW/cm2. If the waveguide core contains polymer layers with different glass transition temperatures, the layers can be poled independently to maximize the overlap integral, and similar pump depletions may be achieved over a distance of approximately 500 μm.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Influence of target properties and laser fluence on energetic protons accelerated by a laser-produced plasma

Takuya Nayuki, Yuji Oishi, Takashi Fujii, Kei Takano, Xiaofang Wang, Alexander Alekseevitch Andreev, Koshichi Nemoto, and Ken-ichi Ueda

J. Appl. Phys. 100, 043111 (2006); http://dx.doi.org/10.1063/1.2266312 (4 pages) | Cited 7 times

Online Publication Date: 22 August 2006

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The dependences of the observed maximum proton energy on laser fluence, and the type and thickness of the target material were studied. The maximum proton energy depended on the laser fluence rather than on the laser intensity for laser pulses with energies between 40 and 430 mJ and pulse durations between 55 and 400 fs. The maximum proton energy increased as the product of target thickness and target mass density decreased. When a polyimide tape target of 7.5 μm thickness was irradiated, the observed maximum proton energy and flux, counted as the number of etched tracks with a solid angle of 0.25 sr, were 3.3±0.1 MeV and 4×106/MeV/shot, respectively. For efficient proton acceleration when a wide ion emission angle is acceptable, polyimide was suitable for the tape target because it contains much hydrogen, and furthermore, it has a low mass density and a high tensile strength.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.Tx Emission, absorption, and scattering of particles
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

A pump-and-probe method for the characterization of nonlinear material parameters within Fabry-Pérot microcavities

Stephan Gulde, Selim Jochim, Nikolaj Moll, and Rainer F. Mahrt

J. Appl. Phys. 100, 043112 (2006); http://dx.doi.org/10.1063/1.2244521 (6 pages)

Online Publication Date: 23 August 2006

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We present a pump-and-probe method based on optical Fabry-Pérot resonators that allows the characterization of third-order nonlinear materials relevant for all-optical technologies. The experiments show particular nonlinear optical resonator dynamics, which we analyze by numerical simulations. We highlight the pros and cons of our method compared with existing nonlinear material-characterization methods.
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42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Electronic and optical properties of 1.3 μm GaAsSbN/GaAs quantum well lasers

Seoung-Hwan Park

J. Appl. Phys. 100, 043113 (2006); http://dx.doi.org/10.1063/1.2266195 (5 pages) | Cited 3 times

Online Publication Date: 23 August 2006

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The electronic and optical properties of GaAsSbN/GaAs quantum well (QW) laser are investigated using the multiband effective mass theory and the non-Markovian gain model. The results are compared with those of type II GaAsSb/GaAs QW laser using a self-consistent method. The GaAsSbN/GaAs QW structure shows that a relatively low compressive strain is required to obtain 1.3 μm wavelength compared to the GaAsSb/GaAs QW structure. The reduction effect of the compressive strain is shown to be dominant for QW structure with a larger N composition or a thick well width. We know that the GaAsSbN/GaAs QW structure has significantly larger optical gain than the GaAsSb/GaAs QW structure. This is because the interband matrix element of the former is much larger than that of the latter. We expect that the GaAsSbN/GaAs QW structure has the improved lasing characteristic compared to the GaAsSb/GaAs QW structure.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Infrared photoluminescence from erbium-doped spark-processed silicon

Kwanghoon Kim and Rolf E. Hummel

J. Appl. Phys. 100, 043114 (2006); http://dx.doi.org/10.1063/1.2266216 (12 pages) | Cited 2 times

Online Publication Date: 23 August 2006

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The infrared (IR) photoluminescence (PL) of erbium-doped spark-processed silicon (sp-Si) was investigated. In addition to IR photoluminescence of undoped sp-Si (which peaks near 945 nm), the erbium insertion into the sp-Si matrix causes additional structure near 1540 nm, that is, in a wavelength range which is important for telecommunication purposes. Erbium was deposited on a silicon wafer followed by spark processing, which enables diffusion of some erbium into the SiOx matrix, thus achieving optoelectronically active spark-processed silicon. Rapid thermal annealing enhances the 1.54 μm wavelength intensity. The optimal processing conditions that result in the most efficient photoluminescence have been established and are presented. In contrast to erbium-doped crystalline silicon, whose light emission is highly affected by temperature (103 times reduction in intensity when heating from 12 to 150 K), the intensity of erbium-doped spark-processed silicon decreases by only a factor of 4 when heated from 15 to 300 K. The room temperature PL efficiency was found to be 0.3% in contrast to erbium-doped crystalline Si whose PL efficiency is known to be 0.05%. The experimental findings are interpreted by postulating a photoluminescence mechanism with energy transfer from spark-processed silicon to the Er3+ ions and by light emission from intrashell energy transition from math→math.
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78.55.Ap Elemental semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.72.Cc Kinetics of defect formation and annealing

Classical coupled oscillators model of the rational harmonic mode locked laser

Wei Li and Gen-Xiang Chen

J. Appl. Phys. 100, 043115 (2006); http://dx.doi.org/10.1063/1.2335598 (7 pages)

Online Publication Date: 25 August 2006

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A coupled modes method is proposed to simulate the active mode locked laser. In this method, the electric fields of optical modes in the laser cavity are treated as free classical oscillators. The optical modulator provides the coupling among them. It is found that the eigenvalue of this coupled system is corresponding to the threshold optical gain, and the eigenfunction is corresponding to the optical field of each mode. The simulation results agree with the Master equation and experiments. Especially the model can be applied to the rational harmonic mode locking case by introducing the concept of ghost modes. The multitrip photons form a set of ghost modes or very weak oscillators. These ghost oscillators play the crucial rule working as the bridge to transfer energy and couple the real cavity modes/oscillators together. The model demonstrates both time domain pulse repetition rate multiplication and the frequency domain mode distribution. The proposed method will help understand the physics of rational harmonic mode locking mechanism and assist the design of devices such as optical pulse generator and multiwavelength laser. Therefore it should have great application in the optical signal generation and processing.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz photonic mixers as local oscillators for hot electron bolometer and superconductor-insulator-superconductor astronomical receivers

I. Cámara Mayorga, P. Muñoz Pradas, E. A. Michael, M. Mikulics, A. Schmitz, P. van der Wal, C. Kaseman, R. Güsten, K. Jacobs, M. Marso, H. Lüth, and P. Kordoš

J. Appl. Phys. 100, 043116 (2006); http://dx.doi.org/10.1063/1.2336486 (4 pages) | Cited 7 times

Online Publication Date: 30 August 2006

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A pump experiment of two astronomical heterodyne receivers, a superconductor- insulator-superconductor (SIS) receiver at 450 GHz and a hot-electron-bolometer (HEB) receiver at 750 GHz, is reported. A low-temperature-grown GaAs metal-semiconductor-metal photonic local oscillator (LO) was illuminated by two near infrared semiconductor lasers, generating a beat frequency in the submillimeter range. I-V junction characteristics for different LO pump power levels demonstrate that the power delivered by the photomixer is sufficient to pump a SIS and a HEB mixer. SIS receiver noise temperatures were compared using a conventional solid-state LO and a photonic LO. In both cases, the best receiver noise temperature was identical (Tsys = 170 K).
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.60.Gz Photodetectors (including infrared and CCD detectors)
95.55.Rg Photoconductors and bolometers

Incident light polarization dependence of terahertz emission spectrum of crystalline 4‐N,N-dimethylamino-4′‐N′-methyl-stilbazolium tosylate

Kazuyoshi Kuroyanagi, Kazuhiro Yanagi, Atsushi Sugita, Hideki Hashimoto, Hironori Takahashi, Shin-ichiro Aoshima, and Yutaka Tsuchiya

J. Appl. Phys. 100, 043117 (2006); http://dx.doi.org/10.1063/1.2335776 (5 pages) | Cited 2 times

Online Publication Date: 31 August 2006

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In this work we have measured the dependence of terahertz emission via optical rectification from the 4‐N,N-dimethylamino-4′‐N′-methyl-stilbazolium tosylate crystal as a function of incident light polarization. Many structures, which varied depending on the polarization of the incident pulse, were observed in the frequency spectra. The observed structures can be explained by incorporating the refractive index dispersion, the response function, and the birefringence properties of the crystal into the mathematical model used to reconstruct the experimental data. Our results show that careful attention must be paid to these three properties when enhancing nonlinear susceptibility during the fabrication of efficient terahertz emitters.
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42.70.Jk Polymers and organics
42.70.Mp Nonlinear optical crystals
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
42.65.An Optical susceptibility, hyperpolarizability

Analysis of tunable photonic crystal directional couplers

Elissavet P. Kosmidou, Emmanouil E. Kriezis, and Theodoros D. Tsiboukis

J. Appl. Phys. 100, 043118 (2006); http://dx.doi.org/10.1063/1.2335800 (9 pages) | Cited 2 times

Online Publication Date: 31 August 2006

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Tunable directional coupler structures based on triangular photonic crystal lattices are investigated using the finite difference time domain method. The infiltration of nematic liquid crystal materials into the coupler waveguides allows for the control of its properties through the application of external static electric fields, which reorient the nematic director. Strong dynamical shifting of the dispersion curves, along with the decoupling frequencies and the coupling coefficient, is demonstrated. Such features render this class of couplers suitable for a range of applications. The coupling lengths accomplished are quite short even when the interaction region between the two coupler branches is widened. Furthermore, operation as a channel interleaver in wavelength division multiplexing systems is explored, and it is revealed that by proper selection of the geometrical parameters a constant channel separation of 0.8 nm is achieved, with an overall length of a few hundreds of microns in wide frequency ranges.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
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X-ray induced pinhole closure in point-projection x-ray radiography

A. B. Bullock, O. L. Landen, B. E. Blue, J. Edwards, and D. K. Bradley

J. Appl. Phys. 100, 043301 (2006); http://dx.doi.org/10.1063/1.2229737 (7 pages) | Cited 4 times

Online Publication Date: 18 August 2006

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In pinhole-assisted point-projection x-ray radiography (or “backlighting”), pinholes are placed between the sample of interest and an x-ray source (or “backlighter”) to effectively limit the source size and hence improve the spatial resolution of the system. Pinholes are generally placed close to such x-ray backlighters to increase the field of view, leading to possible vaporization and pinhole closure due to x-ray driven ablation, thereby potentially limiting the usefulness of this method. An experimental study and modeling of time-dependent closure and resolution is presented. The pinhole closure time scale is studied for various pinhole sizes, pinhole-to-backlighter separations, and filtering conditions. In addition the time-dependent resolution is extracted from one-dimensional wire imaging prior to pinhole closure. Cylindrical hydrodynamic modeling of the pinhole closure shows reasonable agreement with data, giving us a predictive capability for pinhole closure in future experiments.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.70.La X-ray and γ-ray measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Ph X-ray, γ-ray, and particle generation
52.65.Kj Magnetohydrodynamic and fluid equation

Optical emission spectroscopic studies on laser ablated zinc oxide plasma

K. J. Saji, N. V. Joshy, and M. K. Jayaraj

J. Appl. Phys. 100, 043302 (2006); http://dx.doi.org/10.1063/1.2266260 (5 pages) | Cited 10 times

Online Publication Date: 23 August 2006

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Optical emission spectroscopic studies were carried out on the plasma produced by ablation of zinc oxide target using the third harmonic (355 nm) of Q-switched Nd:YAG laser, in vacuum and at three different ambient gas (oxygen) pressures. The spatial variations of electron density (Ne) and electron temperature (Te) were studied up to a distance of 20 mm from the target surface. The kinematics of the emitted particles and the expansion of the plume edge are discussed. The optimum conditions favorable for the formation of high quality zinc oxide thin films are thereby suggested.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Tx Emission, absorption, and scattering of particles
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.77.Dq Plasma-based ion implantation and deposition
81.05.Dz II-VI semiconductors

Decay of the electron number density in the nitrogen afterglow using a hairpin resonator probe

Nicholas S. Siefert, Biswa N. Ganguly, Brian L. Sands, and Greg A. Hebner

J. Appl. Phys. 100, 043303 (2006); http://dx.doi.org/10.1063/1.2234555 (5 pages) | Cited 5 times

Online Publication Date: 24 August 2006

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A hairpin resonator was used to measure the electron number density in the afterglow of a nitrogen glow discharge (p = 0.25–0.75 Torr). Electron number densities were measured using a time-dependent approach similar to the approach used by Spencer et al. [J. Phys. D 20, 923 (1987)] . The decay time of the electron number density was used to determine the electron temperature in the afterglow, assuming a loss of electrons via ambipolar diffusion to the walls. The electron temperature in the near afterglow remained between 0.4 and 0.6 eV, depending on pressure. This confirms the work by Guerra et al. [IEEE Trans. Plasma. Sci. 31, 542 (2003)] , who demonstrated experimentally and numerically that the electron temperature stays significantly above room temperature via superelastic collisions with highly vibrationally excited ground state molecules and metastables, such as A math.
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52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Collisionless electron power absorption in capacitive radio-frequency plasma sheaths

D. Gahan and M. B. Hopkins

J. Appl. Phys. 100, 043304 (2006); http://dx.doi.org/10.1063/1.2245198 (8 pages) | Cited 6 times

Online Publication Date: 24 August 2006

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A capacitively coupled, rf biased electrode mounted in an inductively coupled plasma reactor is used to investigate rf power coupling through the resulting capacitive sheath. Carefully calibrated current and voltage probes provide the electrical measurements necessary for this investigation. An external negative dc bias enables control over the electron component of the total current arriving at the electrode through the capacitive sheath. Sheath models generally assume that electron loss at the end of the rf cycle is negligible but recent theoretical work indicates that there is a significant difference in power coupled through the sheath when electron loss is permitted. The experimental study presented here confirms this result. Retardation of electron loss to the electrode is accompanied with an increase in rf power absorbed by the electrons in the capacitive sheath. Comparing the current signals with and without electron loss establishes that the measured increase in power is associated with the electron loss phase of the rf cycle, which is consistent with predictions of the earlier theoretical work.
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52.40.Kh Plasma sheaths
52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Hf Plasma-material interactions; boundary layer effects

Ion-beam characteristics of the metal cluster complex of Ir4(CO)12

Yukio Fujiwara, Kouji Kondou, Yoshikazu Teranishi, Hidehiko Nonaka, Toshiyuki Fujimoto, Akira Kurokawa, Shingo Ichimura, and Mitsuhiro Tomita

J. Appl. Phys. 100, 043305 (2006); http://dx.doi.org/10.1063/1.2335401 (9 pages) | Cited 10 times

Online Publication Date: 25 August 2006

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Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex which has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, it has been demonstrated that stable ion beams of Ir4(CO)7+ were produced. Energy dependence of sputtering yield of silicon bombarded with Ir4(CO)7+ ions was investigated at a beam energy from 2 to 10 keV at normal incidence. Experimental results showed that the sputtering yield varied substantially with beam energy. The sputtering yield at 10 keV was higher than that with SF5+ or Ar+ ions by a factor of 3–24, whereas the sputtering yield at 3 keV was lower than that with Ar+ ions. In the case of 2 keV, deposition was found to occur. The substantial variation in the sputtering yields was examined using empirical equations for calculating sputtering yields. It was shown that the high sputtering yield at 10 keV would be due to what is called “nonlinear effect” unique to complex-projectile bombardment. It was also indicated that the substantial variation in the sputtering yield would result from lower kinetic energies of each atom constituting the cluster ions. Further, the deposition was explained by considering changes in surface properties caused by the irradiation of the cluster ions.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
81.05.Cy Elemental semiconductors
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
81.15.Cd Deposition by sputtering

Coupling of a vacuum-ultraviolet-radiation source to a processing system

J. D. Chatterton, G. S. Upadhyaya, J. L. Shohet, J. L. Lauer, R. D. Bathke, and K. Kukkady

J. Appl. Phys. 100, 043306 (2006); http://dx.doi.org/10.1063/1.2335688 (5 pages) | Cited 4 times

Online Publication Date: 31 August 2006

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A hollow capillary array is examined as a coupling window between an electron cyclotron resonance plasma vacuum ultraviolet (vuv) source and a separate processing chamber. The transmission of vuv through the capillary array as a function of wavelength is measured and shown to agree with theoretical calculations. A silicon wafer with a dielectric surface is then placed in the processing chamber and exposed to vuv, both with and without the capillary array. A Kelvin probe is used to measure the surface charge induced on the wafer by photoemission in both cases, which confirms the previously measured transmission values. The results show that a capillary array can efficiently couple vuv radiation from a source to a processing chamber without significant modification in the spectrum and its resulting effects on a material.
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52.77.-j Plasma applications
52.50.Dg Plasma sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
81.05.Cy Elemental semiconductors
61.82.Fk Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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