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Applied Physics Letters

Issue 16 • Date Apr 2005

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Displaying Results 1 - 25 of 84
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Nanoscale Fabry–Pérot Interferometer using channel plasmon-polaritons in triangular metallic grooves

    Page(s): 161101 - 161101-3
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    In this letter, we demonstrate the possibility of an effective nanoscale Fabry–Pérot interferometer in a subwavelength plasmonic waveguide in the form of a triangular groove on a metal surface, guiding channel plasmon-polaritons. The resonant cavity is formed by two semitransparent metal membranes (mirrors) placed into the groove. Effective filtering effect of the cavity is demonstrated, resulting in single-mode output from the cavity. Typical quality factor for the cavity of the resonant length is determined to be Q∼100 for the silver-vacuum structure with the 30° groove angle. Possible ways of increasing this factor are discussed. View full abstract»

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  • Low threshold edge emitting polymer distributed feedback laser based on a square lattice

    Page(s): 161102 - 161102-3
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    We report the demonstration of a low-threshold, edge-emitting polymer distributed feedback laser based on a square lattice. The lattice constant was 268 nm, which corresponds to a lattice line spacing in the ΓM symmetry direction of the Brillouin zone of 189 nm. The latter was employed to provide feedback at 630 nm via a first order diffraction process. The device operated on two longitudinal modes, which were situated on the band-edge near the M symmetry point. The two modes had thresholds of 0.66 nJ and 1.2 nJ—significantly lower than comparable surface-emitting DFB lasers. Angle dependent photoluminescence experiments were performed to investigate the effect of the square lattice on the laser operation and the origin of the low threshold. View full abstract»

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  • All-optical dynamic correction of distorted communication signals using a photorefractive polymeric hologram

    Page(s): 161103 - 161103-3
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    All-optical real-time dynamic correction of wave front aberrations for image transmission is demonstrated using a photorefractive polymeric hologram. The material shows video rate response time with a low power laser. High-fidelity, high-contrast images can be reconstructed when the oil-filled phase plate generating atmospheric-like wave front aberrations is moved at 0.3 mm/s. The architecture based on four-wave mixing has potential application in free-space optical communication, remote sensing, and dynamic tracking. The system offers a cost-effective alternative to closed-loop adaptive optics systems. View full abstract»

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  • Simple color tuning of phosphorescent dendrimer light emitting diodes

    Page(s): 161104 - 161104-3
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    A simple way of tuning the emission color in solution processed phosphorescent organic light emitting diodes is demonstrated. For each color a single emissive spin-coated layer consisting of a blend of three materials, a fac-tris(2-phenylpyridyl)iridium (III) cored dendrimer (Ir–G1) as the green emitter, a heteroleptic [bis(2-phenylpyridyl)-2-(2-benzo[4,5-α]thienyl)pyridyl]iridium (III) cored dendrimer [Ir(ppy)2btp] as the red emitter, and 4,4-bis(N-carbazolyl) biphenyl (CBP) as the host was employed. By adjusting the relative amount of green and red dendrimers in the blends, the color of the light emission was tuned from green to red. High efficiency two layer devices were achieved by evaporating a layer of electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI) on top of the spin-coated emissive layer. A brightness of 100 cd/m2 was achieved at drive voltages in the range 5.3–7.3 V. The peak external efficiencies at this brightness ranged from 31 cd/A (18 lm/W) to 7 cd/A (4 lm/W). View full abstract»

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  • Fiber-coupled random laser

    Page(s): 161105 - 161105-3
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    We demonstrate that in fiber-coupled random laser, the threshold energy is twofold reduced and the slope efficiency is fivefold increased when the tip of the fiber is relocated from the surface to the depth of the powder volume. High absorption efficiency, 85%, and high conversion efficiency of population inversion to stimulated emission, 90%, make fiber-coupled random laser a promising laser source. The demonstrated 5% quantum slope efficiency of the “ready to use” random laser emission delivered by the fiber can probably be significantly increased after the optimization of the coupling of emission to the fiber. View full abstract»

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  • Broadband difference frequency generation around phase-match singularity

    Page(s): 161106 - 161106-3
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    It is shown that a wide tunability range of greater than 500 nm can be obtained in the 2 μm band in an 18 mm long periodically poled lithium niobate chip with a single quasiphase-matching grating period at a constant temperature. This letter demonstrates the difference frequency generation bandwidth. A tunable bandwidth of over 130 nm is experimentally confirmed in the 2 μm region. This broad bandwidth can be realized by means of the phase-match curve distortion caused by the phase-match singularity. The wavelength conversion temperature dependence is also shown for several quasiphase-matching grating periods. View full abstract»

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  • Single-shot autocorrelation at relativistic intensity

    Page(s): 161107 - 161107-3
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    We demonstrate the single-shot autocorrelation of an ultrashort laser pulse at relativistic intensity (above 1018 W/cm2). The pulse is divided into two equally strong laser pulses which are focused into a He-gas jet under an angle of 180°. Nonlinear Thomson scattering from plasma electrons is used as second-order autocorrelation signal. View full abstract»

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  • Optical microfiber loop resonator

    Page(s): 161108 - 161108-3
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    We experimentally demonstrate an optical microfiber loop resonator. The resonator was formed in free space by creating a loop from the subwavelength-diameter waist of a short biconical optical fiber taper. The loop length was chosen so that the free spectrum range of the resonator was ∼100 GHz at the optical communication wavelengths near 1.5 μm. In order to change and optimize the spectral characteristics such as the effect of birefringence, the shape of resonances, and the free spectrum range, we manually varied the microfiber self-coupling by alignment of the input and output ends of the loop, which were attached to each other by Van der Waals and electrostatic forces. In particular, we tuned the microfiber loop resonator to exhibit resonances with a Q-factor exceeding 15 000 (finesse ≈10) and, also, to the regime of critical coupling with the extinction ratio of transmission oscillations exceeding 34 dB. This paper was in press when we achieved the values of 95 000 and 630 000 for the loaded and intrinsic Q-factor, respectively (see note added in proof). We believe that the demonstrated Q-factor can be significantly enhanced with the more uniform microfiber. View full abstract»

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  • Tellurite glasses for ultrabroadband fiber Raman amplifiers

    Page(s): 161109 - 161109-3
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    Tellurite glasses optimized for higher Raman gain and broad bandwidth have been realized. These glasses were found to have improved thermal stabilities, which make them suitable for fiber devices applications. While maintaining the Raman gains at higher values, the Raman bandwidths could be broadened by proper addition of alkaline earth oxides and heavy metal oxides in to the tellurite glasses. The relative Raman gain and Raman cross sections of the present glasses are better than the tellurite-based glasses reported earlier. Thus, higher Raman gain and much broader Raman amplifications could be possible by using this tellurite glass system as a gain medium compared with the conventional tellurite-based fiber Raman amplifiers. View full abstract»

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  • Out-of-plane microlens array fabricated using ultraviolet lithography

    Page(s): 161110 - 161110-3
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    This letter describes a three-dimensional ultraviolet-lithography (UV-lithography) process for fabricating an out-of-plane microlens array that can be prealigned with other optical components in an integrated optical bench or easily integrated into microfluidic devices. This microlens array is fabricated with a unique UV-lithography technique, and the desired surface profiles are obtained from top rows to lower rows. The microlens’ focal lengths, diameters of focal pads, depths of focus, and surface profiles are measured and reported herein. This microlens array can be prealigned with another microlens array or other optical components on the same substrate to obtain a truly integrated free-space optical bench. In addition, the fill factor of this microlens array approaches 100%. View full abstract»

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  • Ultrafast optical switching with CdTe nanocrystals in a glass matrix

    Page(s): 161111 - 161111-3
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    This letter describes a principle demonstration of an ultrafast optical switch operating at 1 Tbit/s using CdTe-quantum-dots-doped glasses. Using a three-beam pump and probe experiment, we showed that thermal effects are responsible for a baseline in the pump and probe graphs and the nonexistence of carrier accumulation effects. After eliminating the thermal effects, we showed that, when two pump pulses are delayed by 1 ps, each pump pulse modulates the probe pulse independently, making this material highly promising for ultrafast all optical switching. View full abstract»

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  • Near-field and far-field dynamics of (Al,In)GaN laser diodes

    Page(s): 161112 - 161112-3
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    Near- and far-field dynamics of edge-emitting (Al,In)GaN laser diodes are measured simultaneously with a 100 nm spatial and a 5 ns temporal resolution using a scanning near-field microscope. We reconstruct the phase distribution at the laser diode facet. Beam steering and near-field mode dynamics are interpreted in terms of thermal and carrier induced change of refractive index in the waveguide. View full abstract»

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  • Nanoimprinted strain-controlled elastomeric gratings for optical wavelength tuning

    Page(s): 161113 - 161113-3
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    We demonstrate strain-controlled gratings made of an organic elastomer, polydimethylsiloxane (PDMS), which can achieve optical wavelength tuning by varying their spatial periods. The whole device structure presented in this work incorporates a nanoimprinted PDMS grating integrated with electrostatic microelectromechanical systems actuators on a silicon chip. The fabrication of the device combines polymer soft lithography, nanoimprint lithography, and silicon micromachining across multiscale dimensions ranging from a few hundred nanometers to a few millimeters. The fine tuning capability with fast dynamic response of our PDMS/silicon hybrid optical grating device makes it attractive for use in various micro-optical instruments. View full abstract»

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  • Quantum-cascade lasers without injector regions operating above room temperature

    Page(s): 161114 - 161114-2
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    We present above-room-temperature operation of an injectorless quantum-cascade (QC) laser. The active region is designed as a four-level staircase and has been realized in the strain-compensated material system Ga0.4In0.6As/Al0.56In0.44As based on InP. In pulsed operation the lasers work up to a heat-sink temperature of 340 K, the highest temperature achieved so far with injectorless QC lasers. A large wavelength shift is observed for higher bias fields and (therefore) at high temperatures (10 μm at 77 K and 8.4 μm at 300 K). View full abstract»

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  • Lithium niobate ridge waveguides and modulators fabricated using smart guide

    Page(s): 161115 - 161115-3
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    Ridge waveguides are fabricated using submicron thin films of lithium niobate prepared by crystal ion slicing and wafer bonding (“smart guide”). The waveguides are made by physical etching the lithium niobate thin film using ion beam milling. The waveguides are low loss. An electro-optic polarization modulator with VπL of 15 V cm at λ=1.55 μm is demonstrated using the waveguides. View full abstract»

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  • 9.2-W diode–end–pumped Yb:Y2O3 ceramic laser

    Page(s): 161116 - 161116-3
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    We report on a high-power diode–end–pumped polycrystalline Yb:Y2O3 ceramic laser. Under the pump power of 27 W, continuous-wave output power of 9.2 W at 1078 nm has been obtained by using an output coupler of R=96%. The laser had a threshold of 3.1 W and a slope efficiency of 41%. Comparative studies on the laser performance between the Yb:Y2O3 ceramic and the Yb:yttrium aluminum garnet (YAG) single crystal show that at the same doping concentration of 8 at. %, higher laser efficiency can be obtained in the Yb:Y2O3 ceramic laser than in the Yb:YAG single crystal laser. View full abstract»

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  • Intracavity grating-confined all-epitaxial vertical-cavity surface-emitting laser based on selective interface Fermi-level pinning

    Page(s): 161117 - 161117-3
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    An all-epitaxial GaAs-based vertical-cavity surface-emitting laser is demonstrated with an intracavity mode and current-confining grating. The grating uses selective Fermi-level pinning at a heterointerface to confine the current to the same regions as the optical mode. Despite the grating’s “coarseness,” an increase of efficiency is obtained in side-by-side comparison with devices that lack the grating. View full abstract»

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  • Short pitch cholesteric electro-optical device stabilized by nonuniform polymer network

    Page(s): 161118 - 161118-3
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    We have developed a method for stabilization of the uniform lying helix (ULH) texture of short pitch cholesterics in an electro-optical device, based on the flexoelectro-optic effect in such a texture. By using a small concentration of photoreactive liquid crystal monomer (less than 5 wt. %) and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk (localized essentially at both substrate surfaces) which stabilized efficiently the amplitude and the phase modulation modes of the device. Most importantly, the effect of the residual birefringence of the polymeric network in the field-unwound state of the device was eliminated resulting thus in a substantial improvement of device performance. View full abstract»

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  • Single polarized Tm3+ laser in Zn-diffused LiNbO3 channel waveguides

    Page(s): 161119 - 161119-3
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    In this work, laser operation at 1.76 μm in Tm3+:LiNbO3 Zn-diffused channel waveguides is reported. The laser emission is single polarized with the electric field parallel to the optic axis(π-polarization) and operates in continuous-wave regime, at room temperature. The threshold of laser oscillation is in the range of 40 mW, the slope efficiency is around 1%, and both magnitudes are dependent on the channel width, in accordance with the mode overlap between the pump and signal modes within the waveguides. View full abstract»

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  • Cholesteric liquid crystal laser with wide tuning capability

    Page(s): 161120 - 161120-3
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    This letter examines a planar cholesteric cell (CLC) doped with two collocated laser dyes as a one-dimensional photonic crystal. Adding phototunable chiral material (AzoB) allows the CLC photonic crystal to be lased at the band edges of the photonic band gap with a tuning range of over 100 nm. Tuning is performed by irradiating the chiral AzoB material with UV light, causing the material to undergo trans-cis isomerization in the CLC film. The tuning range is the visible region from 563 to 667 nm. Moreover, the tuning is reversible. View full abstract»

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  • Direct measurement of electron density in microdischarge at atmospheric pressure by Stark broadening

    Page(s): 161501 - 161501-3
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    We present a method and results for measurement of electron density in atmospheric-pressure dielectric barrier discharge. The electron density of microdischarge in atmospheric pressure argon is measured by using the spectral line profile method. The asymmetrical deconvolution is used to obtain Stark broadening. The results show that the electron density in single filamentary microdischarge at atmospheric pressure argon is 3.05×1015 cm-3 if the electron temperature is 10 000 K. The result is in good agreement with the simulation. The electron density in dielectric barrier discharge increases with the increase of applied voltage. View full abstract»

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  • Effect of gold coating on local oxidation using an atomic force microscope

    Page(s): 161901 - 161901-3
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    A simple method to enhance atomic force microscopy local oxidation by coating the substrate with a thin layer of gold is reported. The effect of gold coating is demonstrated experimentally by atomic force microscopy oxidation at various thicknesses of gold on Si and InP. Oxide heights reaching 30 nm are easily achieved on silicon at rates 10 times greater than traditional methods. The gold layer is assumed to increase conductance and current during oxidation, thereby reducing decline in growth rates caused by the increasing resistance of the growing oxide layer itself. Improvement in growth rate and height increases with increasing gold thickness up to a maximum height, but beyond that thickness the heights and rates decrease because the gold layer itself becomes a barrier to the migration of oxyions. The presented method is demonstrated to improve the oxidation rate and height on normal and highly resistive substrates, with lower requirements for applied voltage during oxidation. View full abstract»

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  • Atomistic modeling of shock-induced void collapse in copper

    Page(s): 161902 - 161902-3
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    Nonequilibrium molecular-dynamics (MD) simulations show that shock-induced void collapse in copper occurs by emission of shear loops. These loops carry away the vacancies which comprise the void. The growth of the loops continues even after they collide and form sessile junctions, creating a hardened region around the collapsing void. The scenario seen in our simulations differs from current models that assume that prismatic loop emission is responsible for void collapse. We propose a dislocation-based model that gives excellent agreement with the stress threshold found in the MD simulations for void collapse as a function of void radius. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory