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23 Oct 2006

Volume 89, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 173111 (2006); http://dx.doi.org/10.1063/1.2364835 (3 pages)

Florian M. Kolb, Andreas Berger, Herbert Hofmeister, Eckhard Pippel, Ulrich Gösele, and Margit Zacharias
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Electrically tunable two-dimensional holographic photonic crystal fabricated by a single diffractive element

Y. J. Liu and X. W. Sun

Appl. Phys. Lett. 89, 171101 (2006); http://dx.doi.org/10.1063/1.2364471 (3 pages) | Cited 25 times

Online Publication Date: 23 October 2006

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An electrically tunable two-dimensional holographic photonic crystal was fabricated in polymer-dispersed liquid crystal using a single diffraction element, which was a specially designed photomask consisting of three diffraction gratings, which had a period of 4 μm, oriented 120° relative to one another. With the photomask subjected to a collimated Ar+ laser beam operating at 514.5 nm, a two-dimensional spatial light intensity pattern was created by interference of the three first order diffracted beams produced by the mask. The spatial light intensity pattern was then recorded inside a cell filled with the liquid crystal/prepolymer mixture to create a photonic crystal. The photonic crystal structures were observed under an optical microscope. It showed triangular structures with a lattice constant of about 2.50 μm. The diffraction properties and electro-optic tunability were also presented.
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42.70.Qs Photonic bandgap materials
42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
42.79.Dj Gratings

Subwavelength and super-resolution nondiffraction beam

Haifeng Wang, Luping Shi, Gaoqiang Yuan, X. S. Miao, Weilian Tan, and Towchong Chong

Appl. Phys. Lett. 89, 171102 (2006); http://dx.doi.org/10.1063/1.2364693 (3 pages) | Cited 34 times

Online Publication Date: 23 October 2006

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A light spot that is smaller than a half wavelength will subsequently diverge in all directions. In this letter, the authors model a subwavelength (0.42λ) super-resolution light beam which propagates over a long distance without any divergence. This can be achieved by placing a multibelt pure-phase-type binary optical element on the lens pupil. The authors also report a useful approach for designing the optical element, based on vector diffraction theory, which can be used in paraxial and nonparaxial focusing and imaging systems.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design

Second-harmonic generation in periodically poled lithium niobate waveguides fabricated by femtosecond laser pulses

Y. L. Lee, N. E. Yu, C. Jung, B.-A. Yu, I.-B. Sohn, S.-C. Choi, Y.-C. Noh, D.-K. Ko, W.-S. Yang, H.-M. Lee, W.-K. Kim, and H.-Y. Lee

Appl. Phys. Lett. 89, 171103 (2006); http://dx.doi.org/10.1063/1.2364832 (3 pages) | Cited 19 times

Online Publication Date: 23 October 2006

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The authors have demonstrated the second-harmonic generation (SHG) in optical channel waveguides which were fabricated in periodically poled lithium niobate (PPLN) by tightly focused femtosecond laser (781 nm) pulses. The measured quasi-phase-matched wavelength and 3 dB bandwidth for SHG in a 44.8-mm-long PPLN waveguide which has a domain period of 16.6 μm were about 1563 and 0.25 nm, respectively. The value of the index difference between the fundamental and harmonic wavelengths in laser written waveguide was inferred to be 0.047.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.62.-b Laser applications

Femtosecond pump-probe spectroscopy of intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures

C. V.-B. Tribuzy, S. Ohser, S. Winnerl, J. Grenzer, H. Schneider, M. Helm, J. Neuhaus, T. Dekorsy, K. Biermann, and H. Künzel

Appl. Phys. Lett. 89, 171104 (2006); http://dx.doi.org/10.1063/1.2360242 (3 pages) | Cited 12 times

Online Publication Date: 23 October 2006

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Intersubband relaxation dynamics in InGaAs/AlAsSb multiquantum wells (QWs) is studied by single-color femtosecond pump-probe measurements. At early delay times, all samples show an exponential decay of the transient transmission occurring with time constants of the order of a picosecond. The relaxation dynamics at later delay times strongly depend on both QW thickness and doping location. A non-single-exponential decay behavior indicates extra competing relaxation channels, as further confirmed by solving three-level rate equations. It is shown that slowly decaying components are due to electron transfer to states related to indirect valleys in the wells or in the barriers.
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78.67.De Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Probing the population inversion in intersubband laser by magnetic field spectroscopy

M. P. Semtsiv, S. Dressler, W. T. Masselink, G. Fedorov, and D. Smirnov

Appl. Phys. Lett. 89, 171105 (2006); http://dx.doi.org/10.1063/1.2361200 (3 pages) | Cited 7 times

Online Publication Date: 23 October 2006

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The magnetic field dependence of the midinfrared quantum-cascade laser emission spectra is used to identify the particular Wannier-Stark states responsible for the laser action in two different laser designs. The active regions in both quantum-cascade lasers are based on a modified bound-to-continuum design, but have differing degrees of coupling between the injector miniband and the bound state. The effects of the magnetic field and the injection-barrier width on the emission wavelength indicate that the laser emission in the quantum-cascade laser with less coupling between the injector and the bound state originates from a transition between the injector and extractor minibands. The transition from injector miniband to extractor miniband has both a lower energy and a lower oscillator strength than the transition originating from the bound state, but dominates because of the low population of the upper bound state. This result has important implications for further miniband engineering of quantum-cascade-laser active regions for laser action at the shortest possible wavelengths.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Evaluation of radiative efficiency in InGaN blue-violet laser-diode structures using electroluminescence characteristics

H. Y. Ryu, K. H. Ha, J. H. Chae, K. S. Kim, J. K. Son, O. H. Nam, Y. J. Park, and J. I. Shim

Appl. Phys. Lett. 89, 171106 (2006); http://dx.doi.org/10.1063/1.2364273 (3 pages) | Cited 12 times

Online Publication Date: 23 October 2006

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The authors analyzed radiative efficiency of InGaN laser diodes (LDs) emitting at 405 nm. Based on semiconductor rate equations, the radiative efficiency is unambiguously determined by the analysis of electroluminescence characteristics. The radiative efficiency exceeds 70% even far below threshold of ∼ 3 mA at a high temperature of 80 °C. This highly radiative characteristic is attributed to reduced contribution of nonradiative recombination in LDs with low-dislocation-density active material. It is also found that the radiative efficiency is almost independent of threshold current, indicating that nonradiative recombination is not a major factor which determines lasing threshold in 405 nm emitting InGaN LDs having low dislocation density.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.60.Fi Electroluminescence

Optical absorption by a semiconductor in the presence of intense radiation fields

W. Xu

Appl. Phys. Lett. 89, 171107 (2006); http://dx.doi.org/10.1063/1.2364855 (3 pages) | Cited 8 times

Online Publication Date: 24 October 2006

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Motivated by a recent experiment, the author presents a theoretical study on optical absorption in a semiconductor subjected to pump and probe radiation fields. The electron and hole interactions with midinfrared pump and probe fields are considered and the absorption coefficient is calculated on the basis of a Boltzmann equation approach. It is found that the results obtained theoretically are in line with those observed experimentally and can be used to understand important experimental findings such as the optical absorption in the forbidden zone and the dependence of the absorption of the probe field on intensity and frequency of the pump field.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.-j Infrared and Raman spectra

Photon-number state on-demand source by cavity parametric downconversion

Alex Hayat and Meir Orenstein

Appl. Phys. Lett. 89, 171108 (2006); http://dx.doi.org/10.1063/1.2364877 (3 pages) | Cited 5 times

Online Publication Date: 24 October 2006

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The authors propose a realizable scheme for an arbitrary photon-number state on-demand source based on parametric downconversion in a doubly resonant photonic cavity. The signal-wavelength resonance serves as storage for signal photons and the idler-wavelength resonance generates time separation between exiting idler photons, enabling photon-number-resolving detection. The counting of idler photons indicates the desired signal photon-number state, which can be released from the cavity on demand. They analyze the statistics of photon-number states generation and estimate the maximal repetition rates. Performance of the monolithic cavity for signal-storage and idler time spacing is limited, however, by external devices, namely, the long recovery time of existing single-photon detectors.
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42.50.Ar Photon statistics and coherence theory
42.65.Lm Parametric down conversion and production of entangled photons
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Tunnel-assisted manipulation of intersubband polaritons in asymmetric coupled quantum wells

Aji A. Anappara, Alessandro Tredicucci, Fabio Beltram, Giorgio Biasiol, and Lucia Sorba

Appl. Phys. Lett. 89, 171109 (2006); http://dx.doi.org/10.1063/1.2367664 (3 pages) | Cited 15 times

Online Publication Date: 24 October 2006

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The authors report the external control of the polariton ground state by manipulating the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity. The vacuum-field Rabi splitting is varied by means of charge transfer between the energetically-aligned ground subbands of asymmetric tunnel-coupled quantum wells. The authors propose the use of this structure concept for implementing ultrafast modulation of intersubband polaritons.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.Fg Quantum wells

Strong exciton-photon coupling in a microcavity containing layered perovskite semiconductors

A. Brehier, R. Parashkov, J. S. Lauret, and E. Deleporte

Appl. Phys. Lett. 89, 171110 (2006); http://dx.doi.org/10.1063/1.2369533 (3 pages) | Cited 13 times

Online Publication Date: 24 October 2006

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The authors have realized a Pérot-Fabry microcavity containing a two-dimensional layered perovskite-type semiconductor, (C6H5C2H4–NH3)2PbI4, between a dielectric mirror and a metallic mirror. A strong coupling regime between the perovskite exciton and the confined photon mode has been evidenced at room temperature from angular-resolved reflectivity experiments. An anticrossing of 140 meV is observed between the excitonic and cavity modes. (C6H5C2H4–NH3)2PbI4 having a self-organized multiple quantum well structure, they have determined the oscillator strength per quantum well of this structure: 4×1013 cm−2, which is one order of magnitude higher than in conventional inorganic quantum wells.
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78.67.De Quantum wells
78.66.Qn Polymers; organic compounds
71.35.-y Excitons and related phenomena

Ultrafast electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3 μm

D. B. Malins, A. Gomez-Iglesias, S. J. White, W. Sibbett, A. Miller, and E. U. Rafailov

Appl. Phys. Lett. 89, 171111 (2006); http://dx.doi.org/10.1063/1.2369818 (3 pages) | Cited 41 times

Online Publication Date: 24 October 2006

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The authors report a direct measurement of the absorption dynamics in an InAs p‐i‐n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28 μm. The absorption change recovers with characteristic times ranging from 62 ps (0 V) to  ∼ 700 fs (−10 V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Jq Electro-optical effects
78.67.Hc Quantum dots
42.79.Hp Optical processors, correlators, and modulators

Optical determination of the electron effective mass of strain compensated In0.4Ga0.6As0.995N0.005/GaAs single quantum well

LiFang Xu, D. Patel, C. S. Menoni, J. Y. Yeh, L. J. Mawst, and Nelson Tansu

Appl. Phys. Lett. 89, 171112 (2006); http://dx.doi.org/10.1063/1.2364068 (3 pages) | Cited 4 times

Online Publication Date: 24 October 2006

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A detailed line shape analysis of the temperature dependent photoluminescence spectra of In0.4Ga0.6As1−yNy/GaAs quantum well (QW) (y = 0,0.005) is carried out and the relative contribution of free excitons and free carriers to the radiative recombination at different temperature is quantitatively assessed. The analysis extracts the binding energy of the e1-hh1 ground-state exciton which equals 9.72±1.24 and 17.5±0.9 meV for InGaAs and InGaAsN (N = 0.5%) single QW sample, respectively. By using a fractional dimension exciton binding energy model, an electron effective mass of me* = (0.11±0.015)m0 is determined for the highly strained dilute nitride single QW.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
73.20.At Surface states, band structure, electron density of states
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Quasi-phase-matched Čerenkov second-harmonic generation in a hexagonally poled LiTaO3 waveguide

Y. Zhang, Z. Qi, W. Wang, and S. N. Zhu

Appl. Phys. Lett. 89, 171113 (2006); http://dx.doi.org/10.1063/1.2364059 (3 pages) | Cited 6 times

Online Publication Date: 25 October 2006

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The authors reported a type of second-harmonic generation in a hexagonally poled LiTaO3 waveguide. The emerged second-harmonic waves exhibited a hexagonal pattern when projected on a screen behind the waveguide. This frequency conversion process was realized by guided-to-radiated mode interaction. Phase matching for this process was automatically achieved by a quasi-phase-matched Čerenkov configuration.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Grating based electro-optic switch with azo nonlinear optical polymers

Edris Sarailou, Alireza Gharavi, Sirus Javadpour, and Vladimir Shkunov

Appl. Phys. Lett. 89, 171114 (2006); http://dx.doi.org/10.1063/1.2357853 (3 pages) | Cited 11 times

Online Publication Date: 25 October 2006

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Depth grating was inscribed into nonlinear optical (NLO) polymers functionalized with azo chromophores by a simple interferometric apparatus using a continuous wave laser within the absorption bands of NLO polymer. An attenuation of more than 99.5% with a full width at half maximum of ∼ 1.4 nm was obtained for a single grating with a length of ∼ 1 mm. By making use of the Pockels effect, the refractive index of the poled polymer was changed, and consequently the Bragg wavelength and filter transmission shifted. An ∼ 0.17 nm shift in an applied field of about 116 V/μm was obtained in a weakly poled material.
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42.79.Dj Gratings
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.-k Nonlinear optics
42.82.Gw Other integrated-optical elements and systems

Polarization beam splitter based on a two-dimensional photonic crystal of pillar type

Xianyu Ao, Liu Liu, Lech Wosinski, and Sailing He

Appl. Phys. Lett. 89, 171115 (2006); http://dx.doi.org/10.1063/1.2360201 (3 pages) | Cited 31 times

Online Publication Date: 26 October 2006

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Negatively and positively refractive behaviors are achieved in a two-dimensional photonic crystal of pillar type for TE and TM polarizations, respectively, at the same frequency. The photonic crystal is formed by a triangular lattice of silicon pillars of finite height on a silicon substrate. A polarization beam splitter based on such a photonic-crystal slab is demonstrated. Measurements at near infrared wavelengths indicate that two beams of different polarizations can be split with an extinction ratio of over 10 dB in a wide wavelength range.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.82.Gw Other integrated-optical elements and systems
42.70.Qs Photonic bandgap materials

Hexagonal pyramid shaped light-emitting diodes based on ZnO and GaN direct wafer bonding

Akihiko Murai, Daniel B. Thompson, Hisashi Masui, Natalie Fellows, Umesh K. Mishra, Shuji Nakamura, and Steven P. DenBaars

Appl. Phys. Lett. 89, 171116 (2006); http://dx.doi.org/10.1063/1.2364065 (3 pages) | Cited 17 times

Online Publication Date: 26 October 2006

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The authors report on hexagonal pyramid shaped light-emitting diode (LED) based on ZnO and GaN wafer bonding. After direct wafer bonding of an n-type ZnO substrate to a III-nitride LED wafer, O-plane ZnO was selectively etched to form an electrode having a truncated hexagonal pyramid shape. This wafer bonded LED chip was evaluated with optical output power as a function of forward current and was 2.2 times higher than a conventional-type LED chip having thin Ni (5 nm)/Au (10 nm) p-type electrode at forward current condition of 20 mA.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes
81.65.Cf Surface cleaning, etching, patterning

Optimal control of filamentation in air

Roland Ackermann, Estelle Salmon, Noëlle Lascoux, Jérôme Kasparian, Philipp Rohwetter, Kamil Stelmaszczyk, Shaohui Li, Albrecht Lindinger, Ludger Wöste, Pierre Béjot, Luigi Bonacina, and Jean-Pierre Wolf

Appl. Phys. Lett. 89, 171117 (2006); http://dx.doi.org/10.1063/1.2363941 (3 pages) | Cited 12 times

Online Publication Date: 27 October 2006

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The authors demonstrate optimal control of the propagation of ultrashort, ultraintense (multiterawatt) laser pulses in air over distances up to 36 m in a closed-loop scheme. They optimized three spectral ranges within the white-light continuum as well as the ionization efficiency. Optimization results in signal enhancements by typical factors of 2 and 1.4 for the target parameters. The optimization results in shorter pulses by reducing their chirp in the case of white-light continuum generation, while they correct the pulse from its defects and set the filamentation onset near the detector as far as air ionization is concerned.
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42.68.Ay Propagation, transmission, attenuation, and radiative transfer
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Four-wave mixing and modulation instability of continuous optical waves in single-mode optical fibers

Shanliang Liu

Appl. Phys. Lett. 89, 171118 (2006); http://dx.doi.org/10.1063/1.2369646 (3 pages) | Cited 3 times

Online Publication Date: 27 October 2006

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The four-wave mixing (FWM) equations in single-mode fibers are investigated. It is found that there are four types of FWM, two of them are well known and the others have been known little. FWM can lead to modulation instability (MI) of continuous optical waves. The perturbations will rapidly be amplified and become stronger than the pump waves due to FWM. The characteristics of MI induced by different types of FWM are analyzed by numerically solving the FWM equations.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.81.Dp Propagation, scattering, and losses; solitons

Two-photon pumped random laser in nanocrystalline ZnO

E. V. Chelnokov, N. Bityurin, I. Ozerov, and W. Marine

Appl. Phys. Lett. 89, 171119 (2006); http://dx.doi.org/10.1063/1.2370879 (3 pages) | Cited 21 times

Online Publication Date: 27 October 2006

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Thin film of ZnO nanoparticles with dimension of about 5–10 nm were fabricated by the pulsed laser ablation method. By using a femtosecond laser beam at 700 nm to pump micrometer-thick films the authors observed two-photon-induced lasing at 385 nm. Experimentally obtained dependence of the threshold on the excitation spot radius r0 is closer to (1/r02) than to (1/r0), thus suggesting efficiency of the feedback by scattering-random lasing. The experimental data on nonlinear transmission of the film at the wavelength of pumping are presented.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Zz Random lasers
42.60.By Design of specific laser systems
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Influence of internal fields on gain and spontaneous emission in InGaN quantum wells

J. Hader, J. V. Moloney, and S. W. Koch

Appl. Phys. Lett. 89, 171120 (2006); http://dx.doi.org/10.1063/1.2372443 (3 pages) | Cited 3 times

Online Publication Date: 27 October 2006

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Fully microscopic models are used to investigate the structural dependence of InGaN/GaN quantum-well semiconductor-laser gain media. Due to the inherent piezoelectric fields, the amplitudes and spectral positions of gain and spontaneous emission strongly depend on the structural details. It is shown how quantitative experiment/theory comparisons can be used to determine the fields. As a general trend, it is found that the loss current due to spontaneous emission at threshold decreases with well width and indium composition.
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78.66.Fd III-V semiconductors
78.67.De Quantum wells
77.65.-j Piezoelectricity and electromechanical effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultracompact silicon-on-insulator ridge-waveguide mirrors with high reflectance

P. Velha, J. C. Rodier, P. Lalanne, J. P. Hugonin, D. Peyrade, E. Picard, T. Charvolin, and E. Hadji

Appl. Phys. Lett. 89, 171121 (2006); http://dx.doi.org/10.1063/1.2372581 (3 pages) | Cited 14 times

Online Publication Date: 27 October 2006

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Microcavities offering small modal volumes V ≈ 0.6 (λ/n)3 and consisting of two identical tapered Bragg mirrors etched into a monomode silicon-on-insulator ridge waveguide are studied for operation at telecommunications wavelengths. The authors have measured a Q factor of 8900, for a loaded cavity with a peak transmission at resonance in excess of 60%. The measured Q value quantitatively agrees with the calculation results and is 20 times larger than those previously reported for similar geometries without tapers.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors

Characteristics of 1.3 μm quantum-dot lasers with high-density and high-uniformity quantum dots

Takeru Amano, Takeyoshi Sugaya, and Kazuhiro Komori

Appl. Phys. Lett. 89, 171122 (2006); http://dx.doi.org/10.1063/1.2372593 (3 pages) | Cited 10 times

Online Publication Date: 27 October 2006

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The authors realized a five-layered 1.3 μm InAs quantum dot (QD) with a high density and uniformity of 8.0×1010 cm−2/sheet and 23 meV, respectively, by employing an As2 source and a gradient-composition strain reducing layer. Further, the authors demonstrated the 1.3 μm wavelength emission of this five-layered QD laser with a 0.5 mm cavity length and cleaved facet at room temperature. Moreover, the authors could achieve a high modal gain of 43 cm−1 at 1.3 μm because of the high density and uniformity of the QDs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Cumulative contributions of 3s–np (n ≥ 3) transitions in comparing O atom densities in low-pressure Ar–O2 and He–O2 glow discharges

Mohammad Aslam Khan and Abdulaziz M. Al-Jalal

Appl. Phys. Lett. 89, 171501 (2006); http://dx.doi.org/10.1063/1.2364464 (3 pages) | Cited 3 times

Online Publication Date: 26 October 2006

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Many-fold enhancements in the population densities of O atoms in low-pressure glow discharges in Ar–O2 and He–O2 compared with the discharge in pure O2 have been reported in recent years. In some reports, the 3s math–3p math transitions of O atoms around 844.6 or 777.2 nm are considered in estimating the density of atomic oxygen. The authors’ results demonstrate that the contributions of other possible transitions such as 3s math–np math (n>3) directly feeding the lower 3s math levels are also significant and should be included for a better estimate of O atom densities.
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52.80.Hc Glow; corona
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions

Driving frequency effect on electron heating mode transition in capacitive discharge

S. J. You, S. K. Ahn, and H. Y. Chang

Appl. Phys. Lett. 89, 171502 (2006); http://dx.doi.org/10.1063/1.2348739 (3 pages) | Cited 7 times

Online Publication Date: 27 October 2006

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A study was conducted on the dependence of the electron heating mode transition upon driving frequency in capacitive discharge. The evolution of the electron energy distribution functions (EEDFs) over a wide range of gas pressures was investigated at different driving frequencies. Regardless of the driving frequency, the measured EEDFs exhibited a typical evolution of EEDF from bi-Maxwellian distribution to Druyvesteyn-like distribution with gas pressure, signifying the electron heating mode transition from collisionless to collisional heating. However, the gas pressure, which the heating mode transition takes place, significantly decreased as the driving frequency increased. This result is ascribed to the fact that the collisionless stochastic heating becomes inefficient at high frequency compared with collisional heating.
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52.80.Pi High-frequency and RF discharges
52.50.Gj Plasma heating by particle beams
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
02.50.Ey Stochastic processes

High-current oversized annular electron beam formation for high-power microwave research

I. V. Konoplev, A. W. Cross, P. MacInnes, W. He, C. G. Whyte, A. D. R. Phelps, C. W. Robertson, K. Ronald, and A. R. Young

Appl. Phys. Lett. 89, 171503 (2006); http://dx.doi.org/10.1063/1.2363975 (3 pages) | Cited 13 times

Online Publication Date: 27 October 2006

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The authors report the study of a high-current accelerator, capable of producing thin (2 mm) annular, mildly relativistic (450 keV) electron beams (up to 1.5 kA) of diameter of 70 mm. Propagation of an electron beam through a 2 m long, coaxial beam channel, with inner and outer conductor radii of 30 and 40 mm, respectively, was demonstrated with the electron beam current at the beam-channel output measured using a Rogowski coil. The results obtained are compared with those predicted via numerical simulation. The electron beam obtained was used for proof-of-concept work demonstrating the operation of a high-power maser operating at millimeter wavelengths, using two-dimensional distributed feedback.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Bx Electron sources
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
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