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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Quantum key distribution over 122 km of standard telecom fiber

C. Gobby, Z. L. Yuan, and A. J. Shields

Appl. Phys. Lett. 84, 3762 (2004); http://dx.doi.org/10.1063/1.1738173 (3 pages) | Cited 29 times

Online Publication Date: 29 April 2004

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We report a demonstration of quantum key distribution over a standard telecom fiber exceeding 100 km in length. Through careful optimization of the interferometer and single photon detector, we achieve a quantum bit error ratio of 8.9% for a 122 km link, allowing a secure shared key to be formed after error correction and privacy amplification. Key formation rates of up to 1.9 kbit/s are achieved depending upon fiber length. We discuss the factors limiting the maximum fiber length in quantum cryptography. © 2004 American Institute of Physics.
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84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.81.-i Fiber optics
03.67.Dd Quantum cryptography and communication security
03.67.Pp Quantum error correction and other methods for protection against decoherence

Dynamics of polarization modes in photonic crystals based on arrays of vertical-cavity surface-emitting lasers

Gilles Guerrero, Dmitri L. Boiko, and Eli Kapon

Appl. Phys. Lett. 84, 3777 (2004); http://dx.doi.org/10.1063/1.1739269 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2004

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Polarization dynamics in coherent arrays of vertical-cavity surface-emitting lasers are studied experimentally. The two degenerate polarization lasing modes expected in infinitely large arrays are observed at different frequencies in finite-size structures. The frequency splitting increases with decreasing array size and reaches 60 GHz in 2×2 arrays. This splitting is attributed to the coupling of the two polarization states through depolarization and scattering effects at the boundary of the array. Small arrays lase in the two-frequency regime, whereas large ones oscillate in the single-frequency domain. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.55.Tv Photonic crystal lasers and coherent effects

Characterization of phototransistor internal gain in metamorphic high-electron-mobility transistors

Hyo-Soon Kang, Chang-Soon Choi, Woo-Young Choi, Dae-Hyun Kim, and Kwang-Seok Seo

Appl. Phys. Lett. 84, 3780 (2004); http://dx.doi.org/10.1063/1.1739278 (3 pages) | Cited 19 times

Online Publication Date: 29 April 2004

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We characterize the phototransistor internal gain of metamorphic high-electron-mobility transistors (mHEMTs). When the mHEMT operates as a phototransistor, it has internal gain provided by the photovoltaic effect. To determine this internal gain, photoresponse characteristics dominated by the photoconductive effect as well as the photovoltaic effect are investigated. When the device is turned off, it acts as a photoconductor, and by calculating photoconductor gain, the primary photodetected power can be determined, which indicates the absorbed optical power. The ratio between this and the photodetected power due to the photovoltaic effect represents phototransistor internal gain. It is demonstrated that the phototransistor internal gain is function of optical modulation frequency. © 2004 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Control of the spin polarization of photoelectrons/photoions using short laser pulses

Takashi Nakajima

Appl. Phys. Lett. 84, 3786 (2004); http://dx.doi.org/10.1063/1.1739281 (3 pages) | Cited 11 times

Online Publication Date: 29 April 2004

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We present a generic pump-probe scheme to control spin polarization of photoelectrons/photoions by short laser pulses. By coherently exciting fine structure manifolds of a multi-valence-electron system by the pump laser, a superposition of fine structure states is created. Since each fine structure state can be further decomposed into a superposition of various spin states of valence electrons, each spin component evolves differently in time. This means that varying the time delay between the pump and probe lasers leads to the control of spin states. Specific theoretical results are presented for two-valence-electron atoms, in particular for Mg, which demonstrate that not only the degree of spin polarization but also its sign can be manipulated through time delay. Since the underline physics is rather general and transparent, the presented idea may be potentially applied to nanostructures such as quantum wells and quantum dots. © 2004 American Institute of Physics.
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79.60.-i Photoemission and photoelectron spectra
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
32.80.Fb Photoionization of atoms and ions

Propagation loss in GaN-based ridge waveguides

O. Skorka, B. Meyler, and J. Salzman

Appl. Phys. Lett. 84, 3801 (2004); http://dx.doi.org/10.1063/1.1741025 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2004

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GaN ridge waveguides were fabricated by selective area growth in an organometallic vapor phase epitaxial system. The growth enhancement on a 3.5 μm wide exposed channel versus the masked area width was measured. The propagation losses of a series of GaN multimode waveguides, with different widths, were measured by the outscattering technique at λ=488 nm. The internal optical loss of the GaN ridge waveguide was found to be αint ∼ 4.45 cm−1. Sidewall scattering loss (αscat) and the additional optical loss due to metal electrodes were also measured. The fabricated waveguides may be a basic component for integrated optic circuits. © 2004 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
42.79.Gn Optical waveguides and couplers
78.66.Fd III-V semiconductors

Intense longitudinal electric fields generated from transverse electromagnetic waves

Godai Miyaji, Noriaki Miyanaga, Koji Tsubakimoto, Keiichi Sueda, and Ken Ohbayashi

Appl. Phys. Lett. 84, 3855 (2004); http://dx.doi.org/10.1063/1.1748843 (3 pages) | Cited 20 times

Online Publication Date: 29 April 2004

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We present a simple method for generating an intense longitudinal electric field from transverse electromagnetic waves (laser pulses) with radially symmetric polarization, to which a liquid crystal device converts linear polarization with energy efficiency of ∼ 99%. The laser-generated longitudinal electric field was observed in two dimensions and distinguished from the transverse component using the optical Kerr shutter method. The measured amplitude was 1.1 GV/m at the focus of a pulsed Nd:YAG laser beam of 0.25-MW peak-power. © 2004 American Institute of Physics.
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42.62.-b Laser applications
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Reduced threshold current of a quantum dot laser in a short period superlattice of indirect-band gap

Gregory Sun, Richard A. Soref, and Jacob B. Khurgin

Appl. Phys. Lett. 84, 3861 (2004); http://dx.doi.org/10.1063/1.1751606 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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We propose the idea of making quantum dot lasers by embedding direct-band gap quantum dots in a short period superlattice whose band gap is indirect. This technique reduces the threshold current and its temperature dependence. We show that a higher characteristic-temperature T0 can be achieved in a quantum dot laser with indirect GaAs/AlAs superlattice barriers compared to that with direct GaAs barriers. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.63.Kv Quantum dots

InGaN/GaN quantum-well heterostructure light-emitting diodes employing photonic crystal structures

J. J. Wierer, M. R. Krames, J. E. Epler, N. F. Gardner, M. G. Craford, J. R. Wendt, J. A. Simmons, and M. M. Sigalas

Appl. Phys. Lett. 84, 3885 (2004); http://dx.doi.org/10.1063/1.1738934 (3 pages) | Cited 153 times

Online Publication Date: 29 April 2004

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Electrical operation of InGaN/GaN quantum-well heterostructure photonic crystal light-emitting diodes (PXLEDs) is demonstrated. A triangular lattice photonic crystal is formed by dry etching into the top GaN layer. Light absorption from the metal contact is minimized because the top GaN layers are engineered to provide lateral current spreading, allowing carrier recombination proximal to the photonic crystal yet displaced from the metal contact. The chosen lattice spacing for the photonic crystal causes Bragg scattering of guided modes out of the LED, increasing the extraction efficiency. The far-field radiation patterns of the PXLEDs are heavily modified and display increased radiance, up to ∼ 1.5 times brighter compared to similar LEDs without the photonic crystal. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
73.63.Hs Quantum wells

Design of fully spatially coherent extreme-ultraviolet light sources

Ariel R. Libertun, Xiaoshi Zhang, Ariel Paul, Etienne Gagnon, Tenio Popmintchev, Sterling Backus, Margaret M. Murnane, Henry C. Kapteyn, and Ivan P. Christov

Appl. Phys. Lett. 84, 3903 (2004); http://dx.doi.org/10.1063/1.1739276 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2004

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We demonstrate experimentally that, in order to generate fully spatially coherent extreme-ultraviolet (EUV) beams using high-harmonic generation, it is necessary to guide the driving laser beam over long interaction lengths in gas-filled hollow waveguides. Numerical simulations show that, in propagating the laser through a long plasma-filled guide, the laser beam forms a stable eigenmode with uniform spatial phase, even at very high levels of ionization. This results in a compact, highly spatially coherent, EUV source useful for applications in EUV metrology, microscopy, interferometry, and holography. © 2004 American Institute of Physics.
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42.72.Bj Visible and ultraviolet sources
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
02.60.Cb Numerical simulation; solution of equations
42.79.Gn Optical waveguides and couplers
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
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