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8 May 2006

Volume 88, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 193113 (2006); http://dx.doi.org/10.1063/1.2202003 (3 pages)

Fa-Quan He and Ya-Pu Zhao
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Heterodyne speckle velocimetry

M. D. Alaimo, D. Magatti, F. Ferri, and M. A. C. Potenza

Appl. Phys. Lett. 88, 191101 (2006); http://dx.doi.org/10.1063/1.2200396 (3 pages) | Cited 6 times

Online Publication Date: 8 May 2006

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We present a simple method for fluid velocimetry based on the velocity of the heterodyne speckles generated by tracking particles illuminated with coherent light. It works in real time and provides instantaneous two-dimensional velocity mappings in the direction orthogonal to the optical axis, independently of the particle concentration and size, also for subwavelength particles. It also provides the velocity distribution of the fluid over the entire sample thickness. The method has been quantitatively tested by using the motions of rigid diffusers and applied for mapping the flow of a confined fluid.
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47.80.Jk Flow visualization and imaging
47.80.Cb Velocity measurements
06.30.Gv Velocity, acceleration, and rotation
07.60.Ly Interferometers

Relationship between Bragg bandwidth and acoustic aperture of guided acoustooptic interaction

Guofang Fan, Jiping Ning, Enbang Li, Yuan Li, Qun Han, Lianju Shang, and Zhiqiang Chen

Appl. Phys. Lett. 88, 191102 (2006); http://dx.doi.org/10.1063/1.2202116 (2 pages)

Online Publication Date: 8 May 2006

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In this letter, we present a detailed analysis, based on the diffraction of surface acoustic waves, of the relationship between the Bragg bandwidth and the diffraction efficiency in guided acousto-optic interactions. It has been found that the Bragg bandwidth is not always inversely proportional to the acoustic aperture (diffraction efficiency). Therefore, it is possible to simultaneously get high diffraction efficiencies and large bandwidths for a guided acousto-optic device with a single interdigital transducer under certain conditions.
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42.79.Jq Acousto-optical devices
43.38.Zp

Single-mode distributed-feedback interband cascade laser for the midwave infrared

C. S. Kim, M. Kim, W. W. Bewley, J. R. Lindle, C. L. Canedy, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 88, 191103 (2006); http://dx.doi.org/10.1063/1.2202640 (3 pages) | Cited 3 times

Online Publication Date: 8 May 2006

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Continuous-wave single-mode emission near λ = 3.42 μm is obtained from a distributed-feedback (DFB) interband cascade laser. The low-loss DFB mode in the 15-μm-wide ridge is resonant with the gain peak at 110 K, where the maximum single-mode output power is 3 mW. The instrument-limited linewidth is ⩽ 0.5 Å, and the wavelength is linearly tunable over a 4 nm range by varying the temperature from 110 to 125 K (0.28 nm/K), or over 0.6 nm by varying the current from 60 to 83 mA (0.031 nm/mA).
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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
42.60.Fc Modulation, tuning, and mode locking

Stimulated resonance Raman scattering from dye-doped polymer waveguides

Isao Sakata, Shuhei Fujimoto, and Hisao Yanagi

Appl. Phys. Lett. 88, 191104 (2006); http://dx.doi.org/10.1063/1.2203509 (3 pages) | Cited 7 times

Online Publication Date: 8 May 2006

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We have investigated stimulated resonance Raman scattering (SRRS) from dye-doped polymer thin film waveguides. 1,4-bis[2-[N,N-di(p-totyl)amino]phenyl]vinyl]benzene (DADSB) was used as a dye doped in a spin-coated film of poly(vinyl-pyrrolidone) (PVP). Under optical pumping at the absorption edge of DADSB, a very narrow line (full width at half maximum ∼ 0.5 nm) was observed only in the spectral region where the amplified spontaneous emission (ASE) band appeared. This emission line was assigned to SRRS with a Raman shift of 1600 cm−1. The threshold excitation energy for this SRRS is higher than that of the ASE, but the slope efficiency of the SRRS was higher than that of the ASE. The polarization-dependent intensity revealed that the SRRS was propagated by the transverse electric mode in the thin film waveguide as same as the ASE.
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42.55.Mv Dye lasers
42.55.Ye Raman lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.82.Gw Other integrated-optical elements and systems

Surface-emitting photonic-crystal distributed-feedback laser for the midinfrared

M. Kim, C. S. Kim, W. W. Bewley, J. R. Lindle, C. L. Canedy, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 88, 191105 (2006); http://dx.doi.org/10.1063/1.2203234 (3 pages) | Cited 11 times

Online Publication Date: 9 May 2006

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We demonstrate a surface-emitting photonic-crystal distributed-feedback laser, emitting at λ ≈ 3.7 μm from an antimonide type-II “W” active region. While single-mode operation was not achieved, the spectral emission linewidth for cw optical pumping was only 1.3 Å. For pulsed operation with a pump-spot diameter of 0.8 mm, 60% of the nearly circular output beam was transmitted through an aperture with an angular diameter approximately five times that of a Gaussian emitted beam, assuming that the emission area and pump area are the same.
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42.55.Px Semiconductor lasers; laser diodes
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
42.70.Qs Photonic bandgap materials
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Optical generation and spatially distinct interferometric detection of ultrahigh frequency surface acoustic waves

D. H. Hurley

Appl. Phys. Lett. 88, 191106 (2006); http://dx.doi.org/10.1063/1.2203311 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2006

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Generation and interferometric detection of 22 GHz surface acoustic waves (SAWs) using two laterally separated absorption gratings on a Si substrate are presented. Optical phase sensitive detection of SAWs is demonstrated using a modified Sagnac interferometer. The reflection characteristics of the suboptical wavelength grating necessitate the use of only linear polarization. This is accomplished by employing a Faraday rotator to ensure path reversal of the reference and signal pulses. The enhanced sensitivity of the interferometer is exploited to measure the acoustic disturbance on an identical absorption grating at a distance of ∼ 4.5 μm from the generation site.
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43.35.-c
07.60.Ly Interferometers
42.79.Dj Gratings

Fabrication of long microchannels with circular cross section using astigmatically shaped femtosecond laser pulses and chemical etching

Valeria Maselli, Roberto Osellame, Giulio Cerullo, Roberta Ramponi, Paolo Laporta, Luca Magagnin, and Pietro Luigi Cavallotti

Appl. Phys. Lett. 88, 191107 (2006); http://dx.doi.org/10.1063/1.2203335 (3 pages) | Cited 36 times

Online Publication Date: 9 May 2006

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We report on the fabrication of microfluidic channels in fused silica using femtosecond laser irradiation followed by chemical etching. Using an astigmatically shaped beam, we achieve microchannels with circular cross section and length up to 1.5 mm. We use the same femtosecond laser, with different irradiation parameters, to fabricate high quality optical waveguides on the same substrate. The integration of microchannels and waveguides will enable a forthcoming class of biophotonic sensors.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.65.Cf Surface cleaning, etching, patterning
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Gn Optical waveguides and couplers
42.62.-b Laser applications

Large internal quantum efficiency of In-free UV-emitting GaN/AlGaN quantum-well structures

D. Fuhrmann, T. Retzlaff, U. Rossow, H. Bremers, A. Hangleiter, G. Ade, and P. Hinze

Appl. Phys. Lett. 88, 191108 (2006); http://dx.doi.org/10.1063/1.2202109 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2006

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We have achieved dramatic improvement of the internal quantum efficiency (IQE) for ultraviolet-emitting GaN/AlGaN quantum-well (QW) structures. Despite a defect density of a few 109 cm−2 and the use of an In-free QW we achieve best values for the IQE at room temperature of 26%. Under strong nonresonant excitation, the IQE even increases to 38%. We observe a weak dependence of the IQE on excitation power for our structures. This indicates that similar mechanisms as for GaInN-based light emitters are present.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors

Optical bleaching effect in InN epitaxial layers

V. Pačebutas, G. Aleksejenko, A. Krotkus, J. W. Ager, W. Walukiewicz, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 88, 191109 (2006); http://dx.doi.org/10.1063/1.2202117 (3 pages) | Cited 11 times

Online Publication Date: 10 May 2006

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Large optical bleaching effect was found in epitaxial InN layers from Z-scan measurements at 1.054 μm laser wavelength. Optical transmittance increases nearly five times at the largest light intensities used in experiment. The bleaching recovery time shorter than 3 ps was evidenced from time-resolved measurements at this wavelength, which is much faster than the electron lifetimes of 40 and 240 ps determined on two epitaxial layers by visible pump-terahertz probe technique. Spectral investigations of the bleaching effect performed in the wavelength range from 1 to 1.55 μm support the conclusions on a narrow band gap of InN.
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78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Nitride light-emitting diodes grown on Si (111) using a TiN template

N. C. Chen, W. C. Lien, C. F. Shih, P. H. Chang, T. W. Wang, and M. C. Wu

Appl. Phys. Lett. 88, 191110 (2006); http://dx.doi.org/10.1063/1.2202389 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2006

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Nitride light-emitting diodes (LEDs) are grown on a Si (111) substrate with a TiN template. Transmission electron microscopy and x-ray diffraction indicate that the epitaxial relation follows Si(1,1,1)‖TiN(1,1,1)‖AlN(0,0,1), Si[1,1,0]‖TiN[1,1,0], and Si[0,0,1]‖TiN[0,0,1]. The reflectance measurement and simulation results indicate that the TiN can be adopted as a reflector to mitigate the substrate absorption problem, thus increasing the extraction efficiency of nitride LEDs grown on Si.
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85.60.Jb Light-emitting devices

Crack-free fully epitaxial nitride microcavity with AlGaN/GaN distributed Bragg reflectors and InGaN/GaN quantum wells

X. H. Zhang, S. J. Chua, W. Liu, L. S. Wang, A. M. Yong, and S. Y. Chow

Appl. Phys. Lett. 88, 191111 (2006); http://dx.doi.org/10.1063/1.2202702 (3 pages) | Cited 7 times

Online Publication Date: 10 May 2006

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Using metal-organic chemical vapor deposition, we have fabricated fully epitaxial nitride microcavties with AlGaN/GaN distributed Bragg reflectors and InGaN quantum wells as the light emitter. To solve the problem of cracking, a thin AlN anticracking layer was used. The samples were characterized using transmission electron microscope, reflectivity spectroscopy, and photoluminescence spectroscopy. A cavity quality factor of 200 was obtained and the spontaneous emission of cavity mode was measured from a 1λ GaN microcavity, with 40-pair Al0.24Ga0.76N/GaN distributed Bragg reflectors as the bottom and top reflectors and three period In0.10Ga0.90N/GaN quantum wells in the GaN cavity layer.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Exciton related stimulated emission in ZnO polycrystalline thin film deposited by filtered cathodic vacuum arc technique

X. H. Zhang, S. J. Chua, A. M. Yong, H. D. Li, S. F. Yu, and S. P. Lau

Appl. Phys. Lett. 88, 191112 (2006); http://dx.doi.org/10.1063/1.2202728 (3 pages) | Cited 6 times

Online Publication Date: 10 May 2006

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Random lasing was observed from ZnO polycrystalline thin film deposited by filtered cathodic vacuum arc technique. It is found that the random lasing action results from exciton-exciton scattering process when the excitation intensity is low. However, with increasing excitation intensity, the well-resolved discrete lasing modes evolve into broad stimulated emission band due to electron-hole plasma formation when the photogenerated exciton density exceeds the Mott density. The short spontaneous emission decay time measured at low temperature suggests that the radiative recombination rate is enhanced by the nanosized ZnO grains in the polycrystalline film through exciton-light coupling.
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78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes
71.35.-y Excitons and related phenomena
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
73.50.Mx High-frequency effects; plasma effects

Spectral cross-talk in dual-band quantum well infrared detectors

Alexandru Nedelcu, Xavier Marcadet, Odile Huet, and Philippe Bois

Appl. Phys. Lett. 88, 191113 (2006); http://dx.doi.org/10.1063/1.2203207 (3 pages) | Cited 6 times

Online Publication Date: 10 May 2006

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We propose a general definition of the spectral cross-talk in dual-band infrared (IR) photodetectors, based on the common information carried by the spectral channels. This definition includes detector characteristics as well as scene characteristics and can be applied to any real configuration. We use it to evaluate narrowband and wideband quantum well infrared photodetector structures and set up their interest for dual-band imaging. The spectral cross-talk is negligible for interband IR (3–5 μm/8–12 μm) applications and can be minimized for intraband IR (8–12 μm) applications by properly tailoring the responsivity peaks.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

All-optical pulse data generation in a semiconductor optical amplifier gain controlled by a reshaped optical clock injection

Gong-Ru Lin, Yung-Cheng Chang, and Kun-Chieh Yu

Appl. Phys. Lett. 88, 191114 (2006); http://dx.doi.org/10.1063/1.2203213 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2006

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Wavelength-maintained all-optical pulse data pattern transformation based on a modified cross-gain-modulation architecture in a strongly gain-depleted semiconductor optical amplifier (SOA) is investigated. Under a backward dark-optical-comb injection with 70% duty-cycle reshaping from the received data clock at 10 GHz, the incoming optical data stream is transformed into a pulse data stream with duty cycle, rms timing jitter, and conversion gain of 15%, 4 ps, and 3 dB, respectively. The high-pass filtering effect of the gain-saturated SOA greatly improves the extinction ratio of data stream by 8 dB and reduces its bit error rate to 10−12 at −18 dBm.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
02.50.-r Probability theory, stochastic processes, and statistics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Molecular beam epitaxial growth window for high-quality (Ga,In)(N,As) quantum wells for long wavelength emission

Fumitaro Ishikawa, Michael Höricke, Uwe Jahn, Achim Trampert, and Klaus H. Ploog

Appl. Phys. Lett. 88, 191115 (2006); http://dx.doi.org/10.1063/1.2202113 (3 pages) | Cited 10 times

Online Publication Date: 11 May 2006

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We grow high-quality (Ga,In)(N,As) quantum wells containing 36% In and 4.5% N by molecular beam epitaxy, with a low As pressure and low substrate temperature growth concept. A V/III beam equivalent pressure ratio of 5 and a substrate temperature of 375 °C lead to highly regular ten-period multiple quantum well structures having abrupt interfaces and smooth surfaces. By varying the quantum well width from 4 to 8 nm, we observe 1.34–1.6 μm emission of narrow linewidth ( ⩽ 50 meV) at room temperature after annealing. The large conduction band offset of 410 meV estimated from calculations is beneficial for a material system considered for high temperature laser operation.
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68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Fg Quantum wells
61.72.Cc Kinetics of defect formation and annealing
42.70.Hj Laser materials

Adaptive lens using liquid crystal concentration redistribution

Hongwen Ren, Yi-Hsin Lin, and Shin-Tson Wu

Appl. Phys. Lett. 88, 191116 (2006); http://dx.doi.org/10.1063/1.2202727 (3 pages) | Cited 6 times

Online Publication Date: 11 May 2006

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An adaptive lens using electrically induced liquid crystal (LC)/monomer concentration redistribution is demonstrated. In the absence of an electric field, the LC/monomer mixture is homogeneously distributed. Application of an inhomogeneous electric field causes the LC molecules to diffuse towards the high field region and the liquid monomer towards the low field region. On the other hand, the LC molecules tend to diffuse from high to low concentration direction in order to balance the concentration change. A gradient LC concentration is thus obtained. Using the gradient LC concentration, we demonstrate a tunable-focus lens. Compared with a conventional LC lens, our lens has advantages in small astigmatism and without light scattering, but its response time is slower.
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42.79.Bh Lenses, prisms and mirrors
42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

External cavity multiwavelength semiconductor hybrid mode-locked laser intracavity gain dynamics

Luis C. Archundia and Peter J. Delfyett

Appl. Phys. Lett. 88, 191117 (2006); http://dx.doi.org/10.1063/1.2203228 (3 pages)

Online Publication Date: 11 May 2006

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The intracavity gain dynamics of an external cavity semiconductor hybrid mode-locked laser is measured under multiwavelength operation. The results show a temporal skew between pulses corresponding to different wavelength channels. A measurement of the temporal evolution of the gain reveals a slow gain depletion, avoiding carrier heating and carrier cooling, and decreasing self-phase modulation effects and gain competition between wavelength channels, making multiwavelength operation possible.
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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
42.60.Fc Modulation, tuning, and mode locking
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Multiple wavelength anisotropically polarized mid-infrared emission from InAs quantum dots

D. Wasserman, C. Gmachl, S. A. Lyon, and E. A. Shaner

Appl. Phys. Lett. 88, 191118 (2006); http://dx.doi.org/10.1063/1.2202824 (3 pages) | Cited 7 times

Online Publication Date: 12 May 2006

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Multiple wavelength, anisotropically polarized midinfrared electroluminescence from self-assembled InAs quantum dots grown in AlGaAs/GaAs heterostructures has been observed at 77 K. Electrons are injected into excited quantum dot states using a graded AlGaAs injector. Direct tunneling out of the quantum dot excited states is prevented by means of a superlattice electron filter. Two midinfrared peaks are seen in the electrically pumped surface emission spectra of the device. The emission peaks are orthogonally polarized within the growth plane, indicating photon emission from intersublevel electron transitions within anisotropically shaped quantum dots.
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78.67.Hc Quantum dots
78.30.Fs III-V and II-VI semiconductors
73.21.La Quantum dots
78.60.Fi Electroluminescence
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