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17 Oct 2011

Volume 99, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages)

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black
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Photonic crystal fiber injected with Fe3O4 nanofluid for magnetic field detection

Harneet V. Thakur, Sandipan M. Nalawade, Swati Gupta, Rohini Kitture, and S. N. Kale

Appl. Phys. Lett. 99, 161101 (2011); http://dx.doi.org/10.1063/1.3651490 (3 pages) | Cited 11 times

Online Publication Date: 17 October 2011

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We report a magnetic field sensor having advantages of both photonic crystal fiber and optofluidics, combining them on a single platform by infiltrating small amount of Fe3O4 magnetic optofluid/nanofluid in cladding holes of polarization-maintaining photonic crystal fiber. We demonstrated that magnetic field of few mT can be easily and very well detected with higher sensitivity of 242 pm/mT. The change in the birefringence values has been correlated to the response of nanofluid to applied field.
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42.81.Pa Sensors, gyros
06.30.Ka Basic electromagnetic quantities
42.81.Wg Other fiber-optical devices
42.70.Qs Photonic bandgap materials
75.50.Mm Magnetic liquids

Independent electrical tuning of separated quantum dots in coupled photonic crystal cavities

S. M. Thon, H. Kim, C. Bonato, J. Gudat, J. Hagemeier, P. M. Petroff, and D. Bouwmeester

Appl. Phys. Lett. 99, 161102 (2011); http://dx.doi.org/10.1063/1.3651491 (3 pages) | Cited 3 times

Online Publication Date: 17 October 2011

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Systems of photonic crystal cavities coupled to quantum dots are a promising architecture for quantum networking and quantum simulators. The ability to independently tune the frequencies of laterally separated quantum dots is a crucial component of such a scheme. Here, we demonstrate the independent tuning of laterally separated quantum dots in photonic crystal cavities coupled by in-plane waveguides by implanting lines of protons which serve to electrically isolate different sections of a diode structure.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.67.Hc Quantum dots
42.50.-p Quantum optics

Raman spectroscopy and microscopy based on mechanical force detection

I. Rajapaksa and H. Kumar Wickramasinghe

Appl. Phys. Lett. 99, 161103 (2011); http://dx.doi.org/10.1063/1.3652760 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2011

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The Raman effect is typically observed by irradiating a sample with an intense light source and detecting the minute amount of frequency shifted scattered light. We demonstrate that Raman molecular vibrational resonances can be detected directly through an entirely different mechanism—namely, a force measurement. We create a force interaction through optical parametric down conversion between stimulated, Raman excited, molecules on a surface and a cantilevered nanometer scale probe tip brought very close to it. Spectroscopy and microscopy on clusters of molecules have been performed. Single molecules within such clusters are clearly resolved in the Raman micrographs. The technique can be readily extended to perform pump probe experiments for measuring inter- and intramolecular couplings and conformational changes at the single molecule level.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Be Level crossing and optical pumping
33.15.Bh General molecular conformation and symmetry; stereochemistry
34.20.Gj Intermolecular and atom-molecule potentials and forces

Polariton lasing in a hybrid bulk ZnO microcavity

T. Guillet, M. Mexis, J. Levrat, G. Rossbach, C. Brimont, T. Bretagnon, B. Gil, R. Butté, N. Grandjean, L. Orosz, F. Réveret, J. Leymarie, J. Zúñiga-Pérez, M. Leroux, F. Semond, et al.

Appl. Phys. Lett. 99, 161104 (2011); http://dx.doi.org/10.1063/1.3650268 (3 pages) | Cited 11 times

Online Publication Date: 17 October 2011

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We demonstrate polariton lasing in a bulk ZnO planar microcavity under non-resonant optical pumping at a small negative detuning (δ ∼ −1/6 the 130 meV vacuum Rabi splitting) and a temperature of 120 K. The strong coupling regime is maintained at lasing threshold since the coherent nonlinear emission from the lower polariton branch occurs at zero in-plane wavevector well below the uncoupled cavity mode. The contribution of multiple localized polariton modes above threshold and the non-thermal polariton statistics show that the system is in a far-from-equilibrium regime, likely related to the moderate photon lifetime and in-plane photonic disorder in the cavity.
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42.55.Sa Microcavity and microdisk lasers
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.55.Px Semiconductor lasers; laser diodes

Origin of intrinsic dark count in superconducting nanowire single-photon detectors

T. Yamashita, S. Miki, K. Makise, W. Qiu, H. Terai, M. Fujiwara, M. Sasaki, and Z. Wang

Appl. Phys. Lett. 99, 161105 (2011); http://dx.doi.org/10.1063/1.3652908 (3 pages) | Cited 6 times

Online Publication Date: 18 October 2011

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The origin of the decoherence in superconducting nanowire single-photon detectors, the so-called dark count, was investigated. We measured the direct-current characteristics and bias-current dependencies of the dark count rate in a wide range of temperatures from 0.5 K to 4.0 K, and analyzed the results by theoretical models of thermal fluctuations of vortices. Our results indicate that the current-assisted unbinding of vortex-antivortex pairs is the dominant origin of the dark count.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

Ellipticity dependence of 400 nm-driven high harmonic generation

Sabih D. Khan, Yan Cheng, Max Möller, Kun Zhao, Baozhen Zhao, Michael Chini, Gerhard. G. Paulus, and Zenghu Chang

Appl. Phys. Lett. 99, 161106 (2011); http://dx.doi.org/10.1063/1.3653277 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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We studied the dependence of high harmonic generation efficiency on the ellipticity of 400 nm driving laser pulses at 7.7 × 1014 W/cm2 and compared it with the 800 nm driving laser under the same conditions. The measured decrease of high harmonic yield with the ellipticity of the 400 nm laser is ∼1.5 times slower that of the 800 nm, which agrees well with theoretical predictions based on a semi-classical model. The results indicate that it is feasible to use the generalized double optical gating with 400 nm lasers for extracting single attosecond pulses with high efficiency.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Attenuated total reflection GeO2 hollow waveguide for 9.6–11.7 μm infrared light transmission

Chengbin Jing, Chuanjian Zhang, Yi Li, Yiwei Shi, and Junhao Chu

Appl. Phys. Lett. 99, 161107 (2011); http://dx.doi.org/10.1063/1.3653470 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2011

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We report the preparation and characterization of an attenuated total reflection (ATR) GeO2 hollow waveguide. An internally GeO2-coated silica glass tube (bore size 1.0–1.2 mm, length 1.2 m) was prepared using a homogeneous liquid phase deposition method. Kramers-Kronig analysis reveals that the GeO2 cladding material qualifies as a reflective layer (nr < 1) for the ATR hollow waveguide structure. ATR-transmission of 9.6–11.7 μm light through HE11 mode is confirmed by loss spectrum analysis of the sample. The straight and bending (30°) transmission losses for delivery of a ∼40 W CO2 laser beam (10.6 μm) are 0.56 dB/m and 1.64 dB/m, respectively.
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42.79.Gn Optical waveguides and couplers
42.70.Ce Glasses, quartz

A copper negative index metamaterial in the visible/near-infrared

J. Parsons and A. Polman

Appl. Phys. Lett. 99, 161108 (2011); http://dx.doi.org/10.1063/1.3654149 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2011

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We propose a design for a plasmonic copper metamaterial with a negative index of refraction at visible/near-infrared wavelengths. Using numerical simulations, we demonstrate negative refraction by a copper metamaterial prism and perform a parameter extraction technique to verify the sign of the effective, electric permittivity and magnetic permeability. Our proposed design has a figure of merit comparable to similar silver-based metamaterials operating in the visible/near-infrared range. These findings have implications for the design of low cost plasmonic devices and negative-index metamaterials in the visible/near-infrared.
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78.40.Kc Metals, semimetals, and alloys
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Er Solid metals and alloys

Enhanced performance of InGaN solar cell by using a super-thin AlN interlayer

Liwen Sang, Meiyong Liao, Naoki Ikeda, Yasuo Koide, and Masatomo Sumiya

Appl. Phys. Lett. 99, 161109 (2011); http://dx.doi.org/10.1063/1.3654155 (3 pages) | Cited 6 times

Online Publication Date: 19 October 2011

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A super-thin AlN layer is inserted between the intrinsic InGaN and p-InGaN in the InGaN solar cell structure to improve the photovoltaic property. The dark current is markedly decreased by more than two orders of magnitude and the short-circuit current density is increased from 0.77 mA/cm2 to 1.25 mA/cm2, leading to a doubled conversion efficiency compared to the conventional structure. Electrical transport analysis reveals that the forward electrical property is greatly improved in the range of open circuit voltage and the leakage current mechanism changes from defect related Poole-Frenkel emission to interface tunneling emission. The improvement on the electrical and photovoltaic properties is ascribed to insertion of the AlN interlayer, which not only provides a barrier to reduce tunneling for electrons, but also suppresses the nonradiative recombination.
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88.40.hj Efficiency and performance of solar cells
88.40.jp Multijunction solar cells

Light extraction limits in textured GaN-InGaN light-emitting diodes: Radiative transfer analysis

Oskari Heikkilä, Jani Oksanen, and Jukka Tulkki

Appl. Phys. Lett. 99, 161110 (2011); http://dx.doi.org/10.1063/1.3655155 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2011

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We present a study on the light extraction properties of thin film light-emitting diodes (LEDs) based on the radiative transfer theory. We show that the well known ergodic limit for absorptivity in textured solar cells also applies to emissivity in LEDs accordance with the Kirchhoff’s radiation law. This limit for the emission enhancement by surface texturing in LEDs is fundamental and cannot be exceeded even with index-matched optics. We further carry out numerical calculations accounting for realistic absorption in typical GaN-InGaN LEDs to compare their performance with the ergodic limit for non-absorbing structures. The results show that the optical power of InGaN-GaN LED designs can be improved by a substantial factor of 2–4 with textured surfaces and engineering of the emission pattern and provide a guideline for more efficient LED designs.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Complex Bragg grating writing using direct modulation of the optical fiber with flexural waves

Roberson A. Oliveira, Carlos A. F. Marques, Kevin Cook, John Canning, Rogério N. Nogueira, and Alexandre A. P. Pohl

Appl. Phys. Lett. 99, 161111 (2011); http://dx.doi.org/10.1063/1.3655328 (3 pages) | Cited 4 times

Online Publication Date: 19 October 2011

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A flexural wave is applied to an optical fiber during the process of Bragg grating inscription using the direct writing method through a phase mask. Using this approach, we can dither the writing process to allow complex grating writing. Examples we demonstrate are tunable sampled gratings and phase-shifted gratings.
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42.81.Bm Fabrication, cladding, and splicing
42.81.Wg Other fiber-optical devices
42.79.Dj Gratings

Simulation of a Smith-Purcell free-electron laser with sidewalls: Copious emission at the fundamental frequency

J. T. Donohue and J. Gardelle

Appl. Phys. Lett. 99, 161112 (2011); http://dx.doi.org/10.1063/1.3641471 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2011

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The two-dimensional theory of the Smith-Purcell free-electron laser of Andrews and Brau [H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004)] predicts that coherent Smith-Purcell radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. A particle-in-cell simulation shows that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation can be copiously emitted at the fundamental frequency, for a well-defined range of beam energy.
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41.60.Cr Free-electron lasers
52.65.Rr Particle-in-cell method

Superconducting terahertz metamaterials mimicking electromagnetically induced transparency

Jingbo Wu, Biaobing Jin, Jie Wan, Lanju Liang, Yonggang Zhang, Tao Jia, Chunhai Cao, Lin Kang, Weiwei Xu, Jian Chen, and Peiheng Wu

Appl. Phys. Lett. 99, 161113 (2011); http://dx.doi.org/10.1063/1.3653242 (3 pages) | Cited 4 times

Online Publication Date: 19 October 2011

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We designed and fabricated planar terahertz (THz) metamaterials made from superconducting NbN films to mimic electromagnetically induced transparency (EIT) system. They are characterized using THz time domain spectroscopy over a temperature range from 8 to 300 K. High transmittance and large delay-bandwidth product at transparency window are demonstrated, which mainly arise from the enhanced coupling and decreased damping in superconducting state. The EIT-like spectral response could be tuned in a wide frequency range. By applying two dark resonators with different resonance frequencies coupled with a radiative resonator, we experimentally demonstrated the planar metamaterials mimicking four-level EIT system.
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74.25.Gz Optical properties
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Optical switching of terahertz radiation from meta-atom-loaded photoconductive antennas

Keisuke Takano, Yui Chiyoda, Tsubasa Nishida, Fumiaki Miyamaru, Taku Kawabata, Hirofumi Sasaki, Mitsuo W. Takeda, and Masanori Hangyo

Appl. Phys. Lett. 99, 161114 (2011); http://dx.doi.org/10.1063/1.3654156 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2011

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Optical switching of the spectrum and polarization of terahertz radiation from split-ring resonator-loaded photoconductive antennas has been demonstrated. The switching is based on the sensitivity of the resonance of a split-ring resonator on a photoconductive substrate to a change in the capacitance induced by optical pulse irradiation. The spectral and polarization characteristics of the split-ring resonator-loaded photoconductive antennas are discussed in terms of the coupling between the electric dipole induced by the pump laser and the eigenmodes of the split-ring resonators.
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84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
42.70.-a Optical materials
42.79.-e Optical elements, devices, and systems
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Optical amplification in Er/Yb silicate strip loaded waveguide

Ruimin Guo, Xingjun Wang, Kai Zang, Bing Wang, Lei Wang, Linfei Gao, and Zhiping Zhou

Appl. Phys. Lett. 99, 161115 (2011); http://dx.doi.org/10.1063/1.3655330 (3 pages) | Cited 6 times

Online Publication Date: 20 October 2011

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An Er/Yb silicate strip loaded waveguide was fabricated for optical amplification purpose. A 2.4-μm-wide SiO2 strip was deposited on top of the Er/Yb silicate active layer. Experiment data showed a 5.5 dB signal enhancement in a 7.8-mm-long waveguide pumped by a laser of 372 mW at 1480 nm. The signal is not saturated and can be further enhanced by increasing pumping power and decreasing waveguide loss. The strong red light emission at 660 nm was also observed due to excited state absorption and Yb3+ participated energy transfer upconversion processes.
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42.55.-f Lasers
42.79.Gn Optical waveguides and couplers
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Strong-field single-cycle THz pulses generated in an organic crystal

Christoph P. Hauri, Clemens Ruchert, Carlo Vicario, and Fernando Ardana

Appl. Phys. Lett. 99, 161116 (2011); http://dx.doi.org/10.1063/1.3655331 (3 pages) | Cited 6 times

Online Publication Date: 20 October 2011

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We present high-power single-cycle carrier-envelope phase locked THz pulses at a central frequency of 2.1 THz with MV/cm electric field strengths and magnetic field strengths beyond 0.3 T. The THz radiation is generated by optical rectification in an organic salt crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate called DAST pumped with the signal wavelength of a powerful optical parametric amplifier. Conversion efficiencies of more than 2% are reported.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Polarization-based all-optical logic controlled-NOT, XOR, and XNOR gates employing electro-optic effect in periodically poled lithium niobate

Yinxing Zhang, Yuping Chen, and Xianfeng Chen

Appl. Phys. Lett. 99, 161117 (2011); http://dx.doi.org/10.1063/1.3656000 (3 pages) | Cited 7 times

Online Publication Date: 20 October 2011

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Based on electro-optic Pockels effect of periodically poled lithium niobate, different polarization-based binary all-optical logic functions: controlled-NOT, XOR, and XNOR gates were demonstrated by altering the linear polarization state of input optical signal about 90° on the polarization plant. Because the depletion of signal intensity in polarization-based logic gates is smaller than that of digital logic signal in intensity-based logic gates and almost negligible, this scheme has potential application in realizing complex logic functions by cascading several basic gates.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
84.30.Sk Pulse and digital circuits

Strain-induced tuning of the emission wavelength of high quality GaAs/AlGaAs quantum dots in the spectral range of the 87Rb D2 lines

S. Kumar, R. Trotta, E. Zallo, J. D. Plumhof, P. Atkinson, A. Rastelli, and O. G. Schmidt

Appl. Phys. Lett. 99, 161118 (2011); http://dx.doi.org/10.1063/1.3653804 (3 pages) | Cited 6 times

Online Publication Date: 20 October 2011

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Reversible biaxial strains are used for tuning the emission wavelengths of high quality GaAs/AlGaAs quantum dots (QDs) in the spectral range of the 87Rb D2 lines. The strain is transferred by integrating free standing (Al)GaAs nanomembranes, containing QDs, onto piezoelectric actuators. Narrow excitonic emission lines as sharp as 25 μeV are shown, and a tuning range larger than 5 nm is demonstrated. This range corresponds to an induced anisotropic biaxial strain of the order of 0.15%, as evaluated from the shift in the emission of the GaAs from the nanomembranes. The presented on-chip technology is potentially interesting for future quantum memories based on hybrid semiconductor-atomic interfaces.
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78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
73.21.La Quantum dots

GaN directional couplers for integrated quantum photonics

Yanfeng Zhang, Loyd McKnight, Erman Engin, Ian M. Watson, Martin J. Cryan, Erdan Gu, Mark G. Thompson, Stephane Calvez, Jeremy L. O’Brien, and Martin D. Dawson

Appl. Phys. Lett. 99, 161119 (2011); http://dx.doi.org/10.1063/1.3656073 (3 pages) | Cited 5 times

Online Publication Date: 21 October 2011

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Large cross-section GaN waveguides are proposed as a suitable architecture to achieve integrated quantum photonic circuits. Directional couplers with this geometry have been designed with aid of the beam propagation method and fabricated using inductively coupled plasma etching. Scanning electron microscopy inspection shows high quality facets for end coupling and a well defined gap between rib pairs in the coupling region. Optical characterization at 800 nm shows single-mode operation and coupling-length-dependent splitting ratios. Two photon interference of degenerate photon pairs has been observed in the directional coupler by measurement of the Hong-Ou-Mandel dip [C. K. Hong, et al., Phys. Rev. Lett. 59, 2044 (1987)] with 96% visibility.
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42.82.-m Integrated optics
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
84.40.Az Waveguides, transmission lines, striplines
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.50.-p Quantum optics
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Efficient laser-proton acceleration from an insulating foil with an attached small metal disk

Kazuto Otani, Shigeki Tokita, Toshihiko Nishoji, Shunsuke Inoue, Masaki Hashida, and Shuji Sakabe

Appl. Phys. Lett. 99, 161501 (2011); http://dx.doi.org/10.1063/1.3652705 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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Efficient proton acceleration by the interaction of an intense femtosecond laser pulse with a solid foil has been demonstrated. An aluminum coating (thickness: 0.2 μm) on a polyethylene (PE) foil was irradiated at 2 × 1018 W/cm2 intensity. The protons from the aluminum-disk (diameter: 150 μm to 15 mm) foil were accelerated to much higher energy in comparison with conventional targets such as PE and aluminum-coated PE foils. The fast electron signal along the foil surface was significantly higher from the aluminum-coated PE foil. The laser-proton acceleration appeared to be affected to the size of surrounding conductive material.
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52.38.Kd Laser-plasma acceleration of electrons and ions
29.20.Ej Linear accelerators

Spectroscopic measurement of electric field in atmospheric-pressure plasma jet operating in bullet mode

Goran B. Sretenović, Ivan B. Krstić, Vesna V. Kovačević, Bratislav M. Obradović, and Milorad M. Kuraica

Appl. Phys. Lett. 99, 161502 (2011); http://dx.doi.org/10.1063/1.3653474 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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Atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy. Electric field strength distribution is measured using Stark polarization spectroscopy of He I 492.19 nm line. It is shown that the electric field is almost constant along the jet axis. Measured electric field distribution is in agreement with theoretical predictions of streamer propagation in helium jets at atmospheric pressure. Obtained radial distribution of the axial electric field shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution.
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52.75.-d Plasma devices
52.80.-s Electric discharges
52.25.Ya Neutrals in plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Solitary filamentary structures and nanosecond dynamics in atmospheric-pressure plasmas driven by tailored dc pulses

S. Wu, X. P. Lu, K. Ostrikov, D. Liu, and Y. Pan

Appl. Phys. Lett. 99, 161503 (2011); http://dx.doi.org/10.1063/1.3655201 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2011

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Nanosecond dynamics of two separated discharge cycles in an asymmetric dielectric barrier discharge is studied using time-resolved current and voltage measurements synchronized with high-speed (∼5 ns) optical imaging. Nanosecond dc pulses with tailored raise and fall times are used to generate solitary filamentary structures (SFSs) during the first cycle and a uniform glow during the second. The SFSs feature ∼1.5 mm thickness, ∼1.9 A peak current, and a lifetime of several hundred nanoseconds, at least an order of magnitude larger than in common microdischarges. This can be used in alternating localized and uniform high-current plasma treatments in various applications.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Sb Solitons; BGK modes
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Hc Glow; corona

Simulation of helium discharge ignition and dynamics in thin tubes at atmospheric pressure

Jaroslav Jánský and Anne Bourdon

Appl. Phys. Lett. 99, 161504 (2011); http://dx.doi.org/10.1063/1.3655199 (3 pages) | Cited 7 times

Online Publication Date: 21 October 2011

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Simulations of the influence of electrode geometries on helium discharge ignition and dynamics in thin dielectric tubes are presented. In all studied cases, as observed in experiments, the discharge ignition occurs at the outer edges of the high voltage ring and the influence of the width of the grounded ring on the discharge dynamics is shown. Taking into account the change of permittivity encountered by the discharge as it exits from the tube, the velocity of the discharge front is shown to increase at the tube exit before decreasing downstream similarly to experimental observations.
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52.80.-s Electric discharges
52.25.Mq Dielectric properties
52.65.-y Plasma simulation
52.75.-d Plasma devices

Directional elliptically polarized terahertz emission from air plasma produced by circularly polarized intense femtosecond laser pulses

Fazel Jahangiri, Masaki Hashida, Shigeki Tokita, Takeshi Nagashima, Masanori Hangyo, and Shuji Sakabe

Appl. Phys. Lett. 99, 161505 (2011); http://dx.doi.org/10.1063/1.3651764 (3 pages) | Cited 2 times

Online Publication Date: 21 October 2011

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We have observed directional elliptically polarized terahertz (THz) waves emitted from air plasma produced by circularly polarized femtosecond laser pulses. The spatial distribution of the THz waves shows that the radiation is strongly directed forward with a peak around the laser propagation direction. Measured THz power shows a square dependence on laser energy. We consider the parametric decay of laser light to R-waves in plasma in the presence of a spontaneous magnetic field as a possible explanation for the polarization, power dependence, and direction of the THz beam.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.38.Fz Laser-induced magnetic fields in plasmas
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Dresselhaus field-induced anisotropic spin propagation in ZnSe/BeTe type-II quantum wells

H. Mino, S. Yonaiyama, K. Ohto, and R. Akimoto

Appl. Phys. Lett. 99, 161901 (2011); http://dx.doi.org/10.1063/1.3651758 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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The dynamics of photo-injected electrons and the propagation of photo-created spins in nondoped ZnSe/BeTe type-II quantum wells were investigated by time-resolved photo-induced circular dichroism microscopy at room temperature. Spin propagation from the pump spot presents a directionally dependent spin precession frequency in a magnetic field in Voigt configuration. This anisotropic spin propagation is ascribed to the Dresselhaus effect (G. Dresselhaus, Phys. Rev. 100, 580, 1955) on the radially diffusing photo-injected electrons, since the anisotropy depends on both the directions of crystallographic axis and magnetic field.
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78.20.Ls Magneto-optical effects
81.05.Dz II-VI semiconductors
78.67.De Quantum wells
78.47.D- Time resolved spectroscopy (>1 psec)
78.20.Fm Birefringence
81.07.St Quantum wells
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