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23 Aug 2010

Volume 97, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 081901 (2010); http://dx.doi.org/10.1063/1.3457448 (3 pages)

Zhaofeng Li, Rongkuo Zhao, Thomas Koschny, Maria Kafesaki, Kamil Boratay Alici, Evrim Colak, Humeyra Caglayan, Ekmel Ozbay, and C. M. Soukoulis
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Electrically tunable lasing from a dye-doped two-dimensional hexagonal photonic crystal made of holographic polymer-dispersed liquid crystals

D. Luo, X. W. Sun, H. T. Dai, H. V. Demir, H. Z. Yang, and W. Ji

Appl. Phys. Lett. 97, 081101 (2010); http://dx.doi.org/10.1063/1.3483234 (3 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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Mode-dependent electrically tunable lasing of transverse electric (TE) and transverse magnetic (TM) modes is demonstrated in a dye-doped two-dimensional hexagonal photonic crystal made of holographic polymer-dispersed liquid crystals (LCs). Over 10 nm redshifting in lasing with multiple peaks in nonpolarizing spectra is obtained by applying external voltages up to 40 V. The splitting of lasing spectra between two perpendicular polarizations with the applied voltage is observed, which can be explained through the difference in effective refractive index of LC droplet change with the applied electric field for TE and TM modes.
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42.70.Df Liquid crystals
42.40.-i Holography
42.70.Jk Polymers and organics
42.70.Qs Photonic bandgap materials
42.25.-p Wave optics

High aspect ratio nanochannel machining using single shot femtosecond Bessel beams

M. K. Bhuyan, F. Courvoisier, P. A. Lacourt, M. Jacquot, R. Salut, L. Furfaro, and J. M. Dudley

Appl. Phys. Lett. 97, 081102 (2010); http://dx.doi.org/10.1063/1.3479419 (3 pages) | Cited 17 times

Online Publication Date: 23 August 2010

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We report high aspect ratio nanochannel fabrication in glass using single-shot femtosecond Bessel beams of sub-3 μJ pulse energies at 800 nm. We obtain near-parallel nanochannels with diameters in the range 200–800 nm, and aspect ratios that can exceed 100. An array of 230 nm diameter channels with 1.6 μm pitch illustrates the reproducibility of this approach and the potential for writing periodic structures. We also report proof-of-principle machining of a through-channel of 400 nm diameter in a 43 μm thick membrane. These results represent a significant advance of femtosecond laser ablation technology into the nanometric regime.
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81.16.Rf Micro- and nanoscale pattern formation
81.20.Wk Machining, milling
42.62.Cf Industrial applications
52.38.Mf Laser ablation
79.20.Eb Laser ablation
81.05.Kf Glasses (including metallic glasses)

GaN-based light emitting diodes with embedded SiO2 pillars and air gap array structures

Wei-Chih Lai, Ya-Yu Yang, Li-Chi Peng, Shih-Wei Yang, Yu-Ru Lin, and Jinn-Kong Sheu

Appl. Phys. Lett. 97, 081103 (2010); http://dx.doi.org/10.1063/1.3481692 (3 pages) | Cited 8 times

Online Publication Date: 23 August 2010

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We demonstrated GaN-based light emitting diodes (LEDs) with different embedded heights of SiO2 pillars and air gap array structures. The air gap on top of the SiO2 pillars were also realized using the enhanced epitaxial lateral overgrowth mode. With the embedded SiO2 pillars and air gap array structures, we achieved a smaller reverse leakage current due to the lateral growth-induced crystal quality improvement. Moreover, under 20 mA current injections, the output powers were 3.04, 4.23, 4.66, and 4.44 mW for conventional LED, LEDs with embedded 200 and 500 nm height of SiO2 pillars and air gaps, 500 nm height of SiO2 pillars and air gaps, and 700 and 400 nm height of SiO2 pillars and air gaps, respectively. We found that the embedded 500 nm height SiO2 pillars and 500 nm height air gap array structures could enhance LED output power by more than 50% due to the enhanced guided-light scattering efficiency in our study.
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85.60.Jb Light-emitting devices

A quantum dot based bright source of entangled photon pairs operating at 53 K

A. Dousse, J. Suffczyński, O. Krebs, A. Beveratos, A. Lemaître, I. Sagnes, J. Bloch, P. Voisin, and P. Senellart

Appl. Phys. Lett. 97, 081104 (2010); http://dx.doi.org/10.1063/1.3475487 (3 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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The exciton and biexciton lines of a single quantum dot are deterministically coupled to the optical modes of a photonic molecule. The resonance between the quantum dot emission lines and the molecule cavity modes is reached at 53 K. The device operates as a very bright source of entangled photon pairs, with an extraction efficiency of 40% for each photon of the pair. Our measurements show that the use of Purcell effect allows to quench the exciton spin relaxation during the radiative cascade, at 53 K and at high excitation power.
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42.72.-g Optical sources and standards
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.50.Dv Quantum state engineering and measurements
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
03.67.Mn Entanglement measures, witnesses, and other characterizations

Extraction-controlled quantum cascade lasers

Andreas Wacker

Appl. Phys. Lett. 97, 081105 (2010); http://dx.doi.org/10.1063/1.3483764 (3 pages) | Cited 9 times

Online Publication Date: 24 August 2010

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A simple two-well design for terahertz quantum cascade lasers is proposed which is based on scattering injection and the efficient extraction of electrons from the lower laser level by resonant tunneling. In contrast to existing designs this extraction also controls the positive differential conductivity. The device is analyzed by calculations based on nonequilibrium Green’s functions, which predict lasing operation well above 200 K at a frequency of 2.8 THz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Nonlinear plasmonic directional couplers

José R. Salgueiro and Yuri S. Kivshar

Appl. Phys. Lett. 97, 081106 (2010); http://dx.doi.org/10.1063/1.3482939 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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A study on the nonlinear modes of plasmonic directional couplers created by two nonlinear dielectric slot waveguides with metallic claddings is presented. The calculated power diagram shows substantial differences from the case of nonlinear dielectric couplers. The power-dependent switching and the effect of losses on the coupler performance are studied using finite-difference time-domain numerical simulations.
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84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
02.70.Bf Finite-difference methods

Surface plasmon induced exciton redistribution in ZnCdO/ZnO coaxial multiquantum-well nanowires

B. Liu, C. W. Cheng, R. Chen, S. A. Ekahana, W. F. Yang, S. J. Wang, T. C. Sum, Z. X. Shen, H. J. Fan, and H. D. Sun

Appl. Phys. Lett. 97, 081107 (2010); http://dx.doi.org/10.1063/1.3480414 (3 pages) | Cited 2 times

Online Publication Date: 24 August 2010

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The authors present the surface plasmon effects of Au nanoparticles on the photoluminescence properties of ZnCdO/ZnO coaxial multiquantum-well nanowires fabricated using chemical vapor deposition and pulse laser deposition methods. The spontaneous emission rate from ZnCdO quantum wells was increased by surface plasmon coupling by 1.29 times. The strong plasmon coupling between ZnO barriers and Au nanoparticles provides an extra fast decay channel for excitons generated in ZnO barrier layer and leads to exciton redistribution in ZnCdO/ZnO coaxial quantum wells, which promotes radiative recombination in ZnO barriers but reduces the number of excitons relaxing into the ZnCdO quantum wells.
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68.65.Fg Quantum wells
81.07.St Quantum wells
68.65.La Quantum wires (patterned in quantum wells)
81.07.Gf Nanowires
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors

Ultrathin silicon nitride microring resonator for biophotonic applications at 970 nm wavelength

Ilya Goykhman, Boris Desiatov, and Uriel Levy

Appl. Phys. Lett. 97, 081108 (2010); http://dx.doi.org/10.1063/1.3483766 (3 pages) | Cited 6 times

Online Publication Date: 25 August 2010

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We experimentally demonstrate a high-Q ultrathin silicon nitride microring resonator operating at wavelength of 970 nm that is favorable for large variety of biophotonic applications. Implementation of thin device layer of 200 nm allows enhanced interaction between the optical mode and environment, while still maintaining high quality factor of resonator. In addition, we show the importance of spectral window around 970 nm to improve device sensing capability.
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87.50.wf Biophysical mechanisms of interaction
42.79.-e Optical elements, devices, and systems

Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes

S. Yerci, R. Li, and L. Dal Negro

Appl. Phys. Lett. 97, 081109 (2010); http://dx.doi.org/10.1063/1.3483771 (3 pages) | Cited 20 times

Online Publication Date: 25 August 2010

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Electrical devices based on Erbium (Er) doping of silicon nitride have been fabricated by reactive cosputtering and intense, room temperature Er electroluminescence was observed in the visible (527, 550, and 660 nm) and near-infrared (980 and 1535 nm) spectral ranges at low injection voltages (<5 V EL turn on). The electrical transport mechanism in these devices was investigated and the excitation cross section for the 1535 nm Er emission was measured under electrical pumping, resulting in a value (1.2×10−15 cm2) comparable to optical pumping. These results indicate that Er-doped silicon nitride has a large potential for the engineering of light sources compatible with Si technology.
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85.60.Jb Light-emitting devices

Magnetically assisted quantum cascade laser emitting from 740 GHz to 1.4 THz

Giacomo Scalari, Dana Turčinková, James Lloyd-Hughes, Maria I. Amanti, Milan Fischer, Mattias Beck, and Jérôme Faist

Appl. Phys. Lett. 97, 081110 (2010); http://dx.doi.org/10.1063/1.3481698 (3 pages) | Cited 2 times

Online Publication Date: 25 August 2010

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In this paper we show that by applying a perpendicular magnetic field to a quantum cascade structure it is possible to enhance the gain of different optical transitions. The combination of magnetic confinement with a broadband, cutoff-free optical resonator allows the demonstration of laser action over a large bandwidth, from 733 GHz to 1.38 THz together with the emission at 3.2 THz. A different lasing scheme is revealed that does not rely on resonant tunneling as the main injection mechanism. In combination with the magnetically enhanced gain laser emission at 1 THz is observed up to a temperature of 115 K, which corresponds to a ratio kBT/hν = 2.3 between the lattice thermal energy and the laser photon energy.
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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

Electron spin relaxation time in GaAs/AlGaAs multiple quantum wells grown on slightly misoriented GaAs(110) substrates

Shinji Koh, Akira Nakanishi, and Hitoshi Kawaguchi

Appl. Phys. Lett. 97, 081111 (2010); http://dx.doi.org/10.1063/1.3483768 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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We measured the electron spin relaxation times τs in GaAs/AlGaAs multiple quantum wells (MQWs) grown on slightly misoriented GaAs(110) substrates. The τs of the MQW on misoriented GaAs(110) decreased when the misorientation angles were increased. The bulk inversion asymmetry component of the D’yakonov–Perel’ spin relaxation in the misoriented (110) MQWs was calculated to verify the origin of the decrease in the τs. A comparison between the experimental and calculated results revealed that the decrease in the τs was attributed to the emergence of in-plane effective magnetic fields in the (110) MQWs due to the misorientation.
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73.63.Hs Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
Author Select

Direct measurement of rotationally resolved H2 Q-branch Raman coherence lifetimes using time-resolved picosecond coherent anti-Stokes Raman scattering

Waruna D. Kulatilaka, Paul S. Hsu, Hans U. Stauffer, James R. Gord, and Sukesh Roy

Appl. Phys. Lett. 97, 081112 (2010); http://dx.doi.org/10.1063/1.3483871 (3 pages) | Cited 10 times

Online Publication Date: 26 August 2010

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We report direct measurement of H2 Q-branch Raman coherence lifetimes using time-resolved picosecond coherent anti-Stokes Raman scattering (ps-CARS). A custom-built, high-peak-power, nearly transform-limited ps laser system offers an ideal combination of frequency and temporal resolution for such measurements. The coherence lifetimes measured for pure H2 at room temperature are in good agreement with decay rates that were derived from previous high-resolution studies. Measurements were also performed in binary mixtures of H2–X (X = Ar, N2, CH4, and C2H4). These measurements can be useful for accurate H2 ps-CARS thermometry as well as for studying various H2 collisional energy-transfer processes.
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78.47.je Time resolved light scattering spectroscopy
78.30.-j Infrared and Raman spectra

Semiconductor optical amplifier-based heterodyning detection for resolving optical terahertz beat-tone signals from passively mode-locked semiconductor lasers

Sylwester Latkowski, Ramón Maldonado-Basilio, Kevin Carney, Josué Parra-Cetina, Séverine Philippe, and Pascal Landais

Appl. Phys. Lett. 97, 081113 (2010); http://dx.doi.org/10.1063/1.3481674 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2010

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An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal (and therefore, the beat-tone signal) are resolved by using a photodiode and an electrical spectrum analyzer.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
06.30.Ft Time and frequency
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Effects of gold nanoparticles on electro-optical properties of a polymer-dispersed liquid crystal

Alfonso Hinojosa and Suresh C. Sharma

Appl. Phys. Lett. 97, 081114 (2010); http://dx.doi.org/10.1063/1.3482942 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2010

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We present evidence for relatively large changes in the electro-optical properties of a polymer-dispersed liquid crystal (PDLC) due to inclusion of small concentrations of 14 nm diameter Au-nanoparticles (NPs). We observe that NPs lower switch-on electric field, increase optical transmission at certain voltages, and influence the frequency response of the PDLC.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.45.Wx Polymers and organic materials in electrochemistry

High performance “continuum-to-continuum” quantum cascade lasers with a broad gain bandwidth of over 400 cm−1

Yu Yao, Xiaojun Wang, Jen-Yu Fan, and Claire F. Gmachl

Appl. Phys. Lett. 97, 081115 (2010); http://dx.doi.org/10.1063/1.3484279 (3 pages) | Cited 12 times

Online Publication Date: 27 August 2010

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A quantum cascade laser structure is demonstrated that provides a broadband gain spectrum of 430 cm−1 with a peak emission wavelength around 4.8 μm. The laser active region is based on multiple transitions from strongly coupled upper states to lower laser states. In spite of the broad gain spectrum, high laser performance was demonstrated with low threshold current density (as low as 1.6 kA/cm2), large slope efficiency (over 5 W/A) and high wall plug efficiency (up to 23%) in pulsed mode operation at 295 K.
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42.55.Px Semiconductor lasers; laser diodes

Colossal optical activity of split-ring resonator arrays for millimeter waves

S. Engelbrecht, M. Wunderlich, A. M. Shuvaev, and A. Pimenov

Appl. Phys. Lett. 97, 081116 (2010); http://dx.doi.org/10.1063/1.3481699 (3 pages) | Cited 1 time

Online Publication Date: 27 August 2010

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We have studied the optical activity of bilayered split-ring resonator arrays for millimeter waves. Using quasi-optical technique within controlled polarization rotation we were able to measure transmission and phase shift of these arrays within geometries with parallel and crossed polarizers. We determined experimentally the complex 2×2 transmission matrix which fully characterizes the arrays. We obtain an optical rotation of up to 600 deg/λ for the array thickness of 90 μm and at 3 mm wavelength. The polarization dependence of the optical activity can be effectively suppressed by introducing higher symmetries in the structures. Our results demonstrate the possibility to effectively control and investigate the polarization state of millimeter wave radiation.
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78.20.Ek Optical activity
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
78.70.Gq Microwave and radio-frequency interactions
42.79.-e Optical elements, devices, and systems
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