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2 Jul 2007

Volume 91, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 91, 013501 (2007); http://dx.doi.org/10.1063/1.2753120 (3 pages)

J. Verd, A. Uranga, G. Abadal, J. Teva, F. Torres, F. Pérez-Murano, J. Fraxedas, J. Esteve, and N. Barniol
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Broadband efficient second harmonic generation in media with a short-range order

Yan Sheng, Junhong Dou, Boqin Ma, Bingying Cheng, and Daozhong Zhang

Appl. Phys. Lett. 91, 011101 (2007); http://dx.doi.org/10.1063/1.2754365 (3 pages) | Cited 27 times

Online Publication Date: 2 July 2007

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The authors demonstrate broadband efficient quasiphase matched second harmonic generation (SHG) in nonlinear LiNbO3 crystals. The distribution of ferroelectric domains in a short-range order provides the possibility for broadband second harmonic generation in the visible range. This process is similar to the broadband SHG in random media, but it results in much higher conversion efficiency. The unique distribution of reciprocal vectors provided by the structural short-range order plays an important role in the enhancement. The achieved broadband SHG with high conversion efficiency will aid in the development of optics integration and multiple-channel devices.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Gi Light-sensitive materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Terahertz wave emission and detection using photoconductive antennas made on low-temperature-grown InGaAs with 1.56 μm pulse excitation

A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya

Appl. Phys. Lett. 91, 011102 (2007); http://dx.doi.org/10.1063/1.2754370 (3 pages) | Cited 19 times

Online Publication Date: 2 July 2007

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Photoconductive antennas made on low-temperature-grown Be doped InxGa1−xAs (0.45 ⩽ x ⩽ 0.53) have been investigated focusing on the terahertz emission properties. In the antenna of x = 0.45, the resistance as high as 3 MΩ enabled us to increase the bias field up to 60 kV/cm, and the terahertz waves emitted from the antenna were significantly enhanced. In addition, terahertz waves with the spectral range over 2.5 THz and the peak to noise ratio of 45 dB were generated and detected using only 1.56 μm pulses.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.-q Optoelectronic devices

Transition voltage of asymmetric H state to bend in pi cell

Yubao Sun, Li Jiang, Zaidong Li, Hongmei Ma, and Zhidong Zhang

Appl. Phys. Lett. 91, 011103 (2007); http://dx.doi.org/10.1063/1.2753492 (3 pages) | Cited 1 time

Online Publication Date: 2 July 2007

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The dynamic behavior for the splay to bend transition of pi cell is investigated numerically in detail. When a pi cell has asymmetric pretilt angles, the initial splay configuration changes to asymmetric H state driven by a low voltage, then to bend configuration driven by a pulse voltage that is larger than a transition voltage. The author’s results show that the transition voltage decreases with the increasing pretilt angle, and increases with the increasing anchoring energy and surface viscosity. The transition time is less than 50 ms which is much faster than that of other methods.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Silicon-based light emitters fabricated by embedding Ge self-assembled quantum dots in microdisks

J. S. Xia, K. Nemoto, Y. Ikegami, Y. Shiraki, and N. Usami

Appl. Phys. Lett. 91, 011104 (2007); http://dx.doi.org/10.1063/1.2754356 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2007

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Silicon-based light emitters have been fabricated on silicon-on-insulator substrates by embedding Ge self-assembled quantum dots in microdisk resonators. Strong room-temperature resonant luminescence is observed from the microdisks under optical pumping. Photoluminescence from Ge quantum dots is significantly enhanced by the microdisk resonators. Different kinds of cavity modes, whispering-gallery modes, and Fabry-Pérot modes are observed in the wavelength range from 1.2 to 1.6 μm for microdisks with different diameters.
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85.60.Jb Light-emitting devices
85.35.-p Nanoelectronic devices

Amplification of optical pulse sequences at a high repetition rate in a polymer slab waveguide

D. Amarasinghe, A. Ruseckas, A. E. Vasdekis, G. A. Turnbull, and I. D. W. Samuel

Appl. Phys. Lett. 91, 011105 (2007); http://dx.doi.org/10.1063/1.2753542 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2007

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Amplification of three short light pulses in a 140 ps time window at 5 kHz repetition rate has been demonstrated using a compact amplifier based on the conjugated polymer poly(9,9′-dioctylfluorene-co-benzothiadiazole). The amplifier was optically pumped and gratings were used to couple the signal into and out of the film. A gain of 22 dB was observed for a signal pulse temporally aligned with the pump pulse in a 1 mm waveguide. For a signal pulse delayed by 140 ps, the maximum gain achieved was 14 dB. The results are a step towards the use of polymer amplifiers in data communications.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Scalable fabrication of electrowetting displays with self-assembled oil dosing

B. Sun, K. Zhou, Y. Lao, J. Heikenfeld, and W. Cheng

Appl. Phys. Lett. 91, 011106 (2007); http://dx.doi.org/10.1063/1.2753697 (3 pages) | Cited 15 times

Online Publication Date: 2 July 2007

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Scalable fabrication of electrowetting displays with self-assembled oil dosing is reported. Electrowetting pixel structures consisted of flexible substrate/electrode/hydrophobic dielectric/hydrophilic grid. 20 electrowetting display prototypes were constructed with four pixel sizes ranging from 300×900 to 50×150 μm2 and with five grid thicknesses ranging from 16.2 to 3.3 μm. Self-assembled oil dosing was achieved by dip coating the substrate through an oil film suspended on water. The oil films in pixels were geometrically flat. Operating voltage increased with pixel aspect ratio. Electrical capacitance and optical absorption calculations confirm that oil thickness is within ±5% of the hydrophilic grid height.
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42.79.Kr Display devices, liquid-crystal devices

Optical phonons assisted infrared absorption in VO2 based bolometer

Changhong Chen and Zhiping Zhou

Appl. Phys. Lett. 91, 011107 (2007); http://dx.doi.org/10.1063/1.2753746 (3 pages) | Cited 12 times

Online Publication Date: 3 July 2007

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Optical phonons assisted infrared absorption in VO2 based bolometer is demonstrated to be free, low, or over damping oscillation over different spectral ranges depending on the passivation thickness. In particular, it will become saturated due to the over damping oscillation in the spectral range corresponding to the absorption bands from strong phonon vibrations. The device reaches a peak absorbance of 99.9% at wavelength of 9.1 μm and shows a broadband absorption, independent of metal-insulator transition and radiation incident angle up to 30° in the long wavelength (8–14 μm) infrared region.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.-j Infrared and Raman spectra

Dielectric properties of single-walled carbon nanotubes in the terahertz frequency range

Hisaaki Nishimura, Nobutsugu Minami, and Ryo Shimano

Appl. Phys. Lett. 91, 011108 (2007); http://dx.doi.org/10.1063/1.2753747 (3 pages) | Cited 15 times

Online Publication Date: 3 July 2007

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The authors report on the terahertz time-domain spectroscopy of single-walled carbon nanotubes (SWCNTs) dispersed in a polymer film in a broad frequency range from 0.2 to 20 THz. The complex dielectric function of the composite film is obtained without using Kramers-Kronig analysis, from which the dielectric function of SWCNTs is extracted by using the effective medium theory. The real part of the dielectric function exhibits very large values at low frequency below 2 THz. The conductivity spectrum shows a peak around 3 THz. The spectral behavior is consistent with overdamped Lorentz oscillator model, indicating the response of curvature-induced small-gap SWCNTs.
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77.22.Ch Permittivity (dielectric function)
73.63.Fg Nanotubes
72.30.+q High-frequency effects; plasma effects
78.70.Gq Microwave and radio-frequency interactions

Differential atomic magnetometry based on a diverging laser beam

E. Hodby, E. A. Donley, and J. Kitching

Appl. Phys. Lett. 91, 011109 (2007); http://dx.doi.org/10.1063/1.2753763 (3 pages) | Cited 3 times

Online Publication Date: 3 July 2007

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The authors demonstrate a novel atomic magnetometer that uses differential detection of the spatially diverging components of a light field to monitor the Larmor precession frequency of atoms in a thermal vapor. The design is implemented in compact form with a micromachined alkali vapor cell and a naturally divergent light field emitted by a vertical-cavity surface-emitting laser. Operating the magnetometer in differential mode cancels common-mode noise and improves the sensitivity by a factor of 26 over single-channel operation. They also suggest ways in which the current sensitivity of 28 pT/√Hz may be improved further without sacrificing size or simplicity.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
37.20.+j Atomic and molecular beam sources and techniques
32.80.-t Photoionization and excitation

Multikilowatt chemical oxygen-iodine laser with chemical generation of molecular iodine

Yuelong Zhang, Fengting Sang, Peng Zhang, Yuqi Jin, Benjie Fang, Weili Zhao, Fang Chen, Qingwei Li, and Mingxiu Xu

Appl. Phys. Lett. 91, 011110 (2007); http://dx.doi.org/10.1063/1.2754363 (3 pages) | Cited 1 time

Online Publication Date: 3 July 2007

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A multikilowatt chemical oxygen-iodine laser (COIL) using molecular iodine generated chemically as the iodine source was developed and tested. The COIL, with a gain length of 26.5 cm, was energized by a square pipe-array jet singlet oxygen generator (JSOG), with a nozzle bank having a designed Mach number of 2.5. The JSOG, operating without a primary buffer gas, has a much better operation stability during basic hydrogen peroxide pumping circulations. Iodine injectors/nozzles made of polyimide were used. An output power of 7.8 kW and a chemical efficiency of 24.5% were achieved with a chlorine flow rate of 353 mmole/s.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
82.40.-g Chemical kinetics and reactions: special regimes and techniques

Aggregation-induced emissions of tetraphenylethene derivatives and their utilities as chemical vapor sensors and in organic light-emitting diodes

Yongqiang Dong, Jacky W. Y. Lam, Anjun Qin, Jianzhao Liu, Zhen Li, Ben Zhong Tang, Jiaxin Sun, and Hoi Sing Kwok

Appl. Phys. Lett. 91, 011111 (2007); http://dx.doi.org/10.1063/1.2753723 (3 pages) | Cited 64 times

Online Publication Date: 5 July 2007

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Nonemissive tetraphenylethene (TPE) 1 and its diphenylated derivative 2 were induced to emit intensely by aggregate formation. Crystalline aggregates of the dyes emitted bluer lights than their amorphous counterparts. The emissions of the TPE dyes could be switched off and on continuously and reversibly by wetting and dewetting with solvent vapors, respectively, manifesting their ability to optically sense volatile organic compounds. The light-emitting diodes fabricated from 1 and 2 were turned on at ∼ 2.9 and ∼ 5 V and emitted blue lights with maximum luminance of ∼ 1800 and ∼ 11 000 cd/m2, respectively.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.Jb Light-emitting devices
68.08.Bc Wetting

Differential phase shift quantum key distribution using single-photon detectors based on a sinusoidally gated InGaAs/InP avalanche photodiode

Naoto Namekata, Go Fujii, Shuichiro Inoue, Toshimori Honjo, and Hiroki Takesue

Appl. Phys. Lett. 91, 011112 (2007); http://dx.doi.org/10.1063/1.2753767 (3 pages) | Cited 13 times

Online Publication Date: 5 July 2007

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The authors report a quantum key distribution experiment, in which they implemented a differential phase shift quantum key distribution protocol, using single-photon detectors based on InGaAs/InP avalanche photodiodes operated with a sinusoidal gating. The single-photon detectors were operated at a repetition frequency of 500 MHz with low after pulsing probabilities and low dark counts. A sifted key generation rate of 1.5 Mbit/s was achieved over a communication distance of 15 km. Taking account of the security of the protocol against general individual attacks, secure keys can be generated with a rate of 0.33 Mbit/s.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
03.67.Dd Quantum cryptography and communication security
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Low driving voltage and high stability organic light-emitting diodes with rhenium oxide-doped hole transporting layer

Dong-Seok Leem, Hyung-Dol Park, Jae-Wook Kang, Jae-Hyun Lee, Ji Whan Kim, and Jang-Joo Kim

Appl. Phys. Lett. 91, 011113 (2007); http://dx.doi.org/10.1063/1.2754635 (3 pages) | Cited 54 times

Online Publication Date: 5 July 2007

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The authors report a promising metal oxide-doped hole transporting layer (HTL) of rhenium oxide (ReO3)-doped N,N′-diphenyl-N,N′-bis (1,1′-biphenyl)-4,4′-diamine (NPB). The tris(8-hydroxyquinoline) aluminum-based organic light-emitting diodes with ReO3-doped NPB HTL exhibit driving voltage of 5.2–5.4 V and power efficiency of 2.2–2.3 lm/W at 20 mA/cm2, which is significantly improved compared to those (7.1 V and 2.0 lm/W, respectively) obtained from the devices with undoped NPB. Furthermore, the device with ReO3-doped NPB layer reveals the prolonged lifetime than that with undoped NPB. Details of ReO3 doping effects are described based on the UV-Vis absorption spectra and characteristics of hole-only devices.
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85.60.Jb Light-emitting devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Controlling the polarization correlation of photon pairs from a charge-tunable quantum dot

R. J. Young, S. J. Dewhurst, R. M. Stevenson, A. J. Shields, P. Atkinson, K. Cooper, and D. A. Ritchie

Appl. Phys. Lett. 91, 011114 (2007); http://dx.doi.org/10.1063/1.2754641 (3 pages) | Cited 5 times

Online Publication Date: 5 July 2007

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Correlation between the rectilinear polarizations of the photons emitted from the biexciton decay in a single quantum dot is investigated in a device which allows the charge state of the dot to be controlled. Optimizing emission from the neutral exciton states maximizes the operating efficiency of the biexciton decay. This is important for single dot applications such as a triggered source of entangled photons. As the bias on the device is reduced correlation between the two photons is found to fall dramatically as emission from the negatively charged exciton becomes significant. Lifetime measurements demonstrate that electronic spin-scattering is the likely cause.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena

Fabrication of low loss Ge33As12Se55 (AMTIR-1) planar waveguides

Duk-Yong Choi, Steve Madden, Andrei Rode, Rongping Wang, and Barry Luther-Davies

Appl. Phys. Lett. 91, 011115 (2007); http://dx.doi.org/10.1063/1.2754360 (3 pages) | Cited 9 times

Online Publication Date: 5 July 2007

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The authors describe the fabrication of low loss Ge33As12Se55 rib waveguides. Pulsed laser deposition was used to obtain high quality, dense films with the same stoichiometry as the bulk glass, while standard semiconductor processing was used to pattern the waveguides. They obtained rib waveguides of 3, 4, and 5 μm wide with propagation losses (0.3 dB/cm at 1550 nm) more than ten times lower than previously reported for this material.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Fg Pulsed laser ablation deposition

Quality factors of nonideal micro pillars

N. Gregersen, T. R. Nielsen, B. Tromborg, and J. Mørk

Appl. Phys. Lett. 91, 011116 (2007); http://dx.doi.org/10.1063/1.2751586 (3 pages) | Cited 9 times

Online Publication Date: 6 July 2007

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The influence of fabrication-induced imperfections and material absorption on the quality (Q) factor of a microcavity pillar is studied numerically. The dependence on sidewall inclination, selective underetch, and intrinsic loss is quantified. The authors show that imperfections can lead to an improvement in Q and that a sidewall inclination angle of less than 1° causes a dramatic change in the Q factor. The variations in Q can be attributed to a delicate balance between effective index contrasts, mode overlap, and higher-order mode contributions.
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42.79.-e Optical elements, devices, and systems

Local reconstruction in computed tomography of diffraction enhanced imaging

Zhi-Feng Huang, Li Zhang, Ke-Jun Kang, Zhi-Qiang Chen, Pei-Ping Zhu, Qing-Xi Yuan, and Wan-Xia Huang

Appl. Phys. Lett. 91, 011117 (2007); http://dx.doi.org/10.1063/1.2749427 (3 pages) | Cited 3 times

Online Publication Date: 6 July 2007

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Computed tomography of diffraction enhanced imaging (DEI-CT) based on synchrotron radiation source has extremely high sensitivity of weakly absorbing low-Z samples in medical and biological fields. The authors propose a modified backprojection filtration(BPF)-type algorithm based on PI-line segments to reconstruct region of interest from truncated refraction-angle projection data in DEI-CT. The distribution of refractive index decrement in the sample can be directly estimated from its reconstruction images, which has been proved by experiments at the Beijing Synchrotron Radiation Facility. The algorithm paves the way for local reconstruction of large-size samples by the use of DEI-CT with small field of view based on synchrotron radiation source.
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07.85.Qe Synchrotron radiation instrumentation
42.30.Wb Image reconstruction; tomography

Particle acceleration by subcycle laser pulse in vacuum

Bai-Song Xie, Ming-Ping Liu, Nai-Yan Wang, and M. Y. Yu

Appl. Phys. Lett. 91, 011118 (2007); http://dx.doi.org/10.1063/1.2754357 (3 pages) | Cited 4 times

Online Publication Date: 6 July 2007

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An analytical model based on the diffraction-induced transformation [ A. E. Kaplan, J. Opt. Soc. Am. B 15, 951 (1998) ] for an ultrashort subcycle laser pulse propagating in vacuum is considered. The pulse is initially Gaussian. To the lowest order of the diffraction angle its evolution satisfies Maxwell’s equations. The model is used to study the motion of charged particles in the pulse. It is shown that the delta-function representation is an excellent approximation of a subcycle pulse for studying charged-particle dynamics in subcycle pulse.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
41.75.Jv Laser-driven acceleration
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
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