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Applied Physics Letters

Issue 3 • Date Jan 1992

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Low threshold current grating‐coupled surface‐emitting strained‐InGaAs single quantum well laser with GaAs optical confinement structure

    Page(s): 265 - 267
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    We have demonstrated low threshold current operation of a grating‐coupled surface‐emitting strained‐InGaAs single quantum well laser with a distributed Bragg reflector. By considering the field discontinuity at the gain/grating section interface, our calculations show that the GaAs optical confinement structure can provide high effective reflectivity in the grating section. As a result, continuous wave threshold currents as small as 15 mA were attained at 22 °C, which is the lowest threshold current reported for a grating‐coupled surface‐emitting laser fabricated without epitaxial regrowth. View full abstract»

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  • Quantum wire and dot formation by chemical vapor deposition and molecular layer deposition of one‐dimensional conjugated polymer

    Page(s): 268 - 270
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    Using the reaction between two types of molecules, I [terephthalaldehyde (TPA)] and II [p‐phenylenediamine (PPDA), 4,4’‐diaminodiphenyl ether (DDE), 4,4’‐diaminodiphenyl sulfide (DDS), or 1,4‐diaminodiphenylmethane (DDM)], we fabricate quantum wires and quantum dots by chemical vapor deposition. In the TPA/PPDA film, an exciton absorption peak occurs near 500 nm, indicating that long conjugated chains (quantum wire) are formed. In TPA/DDE, TPA/DDS, and TPA/DDM films, which have quantum dots consisting of three benzene rings separated by barriers of ‐O, ‐S‐, and ‐CH2‐ bonds, blue shifts of the absorption band occur due to an electron confinement. We also demonstrate molecular layer deposition of the TPA/PPDA film. View full abstract»

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  • Broadly tunable LiB3O5 optical parametric oscillator

    Page(s): 271 - 273
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    We report, what is to our knowledge, the first XeCl excimer pumped optical parametric oscillator using critical phase matched LiB3O5 (LBO), to generate broadly tunable coherent radiation with high optical to optical efficiency. Tuning ranges of 355–497 nm in the ultraviolet/blue spectral region, and 809–2.34 μm in the near‐infrared have been obtained, with pump depletions as high as 28%. Oscillation thresholds, external efficiencies, effects of intracavity losses, effects of pump beam size and inherent linewidths (∼0.3 nm) are also reported. View full abstract»

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  • Proton exchanged imbalanced Ti:LiNbO3 Mach‐Zehnder modulator

    Page(s): 274 - 276
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    We describe the fabrication process of a LiNbO3 integrated Mach‐Zehnder interferometer featuring a large path‐imbalance between the arms. This path‐imbalance is created by the proton exchange located on one arm. The proton exchange increases the extraordinary refractive index ne of lithium niobate and modifies the effective index of the guided mode. Path‐differences of 80 μm per mm of proton exchange length are obtained with the fabrication process reported here. View full abstract»

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  • Zero‐loss quantum well waveguide Mach–Zehnder modulator at 1.55 μm

    Page(s): 277 - 279
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    We report the first interferometric waveguide intensity modulator with optical gain. A monolithically integrated compressively strained InGaAs quantum well amplifier provides a net 4.2 dB fiber‐to‐fiber gain at 120 mA forward bias. Reversed‐biased InGaAsP quantum wells provide enhanced electrorefraction for the modulator in which we demonstrate a 3 dB electrical modulation bandwidth of 2.25 GHz. The voltage‐length product for 180° phase shift is a record Vπ × L = 1.9 V mm. The total device length is under 2 mm. View full abstract»

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  • Ferroelectric liquid crystal modulator using twisted smectic structure

    Page(s): 280 - 282
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    We describe an electro‐optic modulator using ferroelectric liquid crystal. A smectic C* material with a 45° tilt angle is sandwiched between two glass plates with buffing directions perpendicular to each other. This produces a twisted smectic structure in absence of an electric field. When used with polarizers, the twisted structure can be electrically distorted to produce optical modulation on a sub‐millisecond time scale using less than 1 V/μm. View full abstract»

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  • Polarized excitation luminescence of semiconductor quantum wells

    Page(s): 283 - 285
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    A new photoluminescence excitation (PLE) spectroscopy technique for the characterization of quantum‐well structures is described. The technique, which requires a standard PLE setup modified to allow for variable control of the excitation beam polarization, provides an unusually simple and unambiguous means for distinguishing between electron‐to‐light‐hole (e‐lh) and electron‐to‐heavy‐hole (e‐hh) near‐gap excitonic optical transitions. Transition types are identified by inspection of the quotient of two PLE spectra obtained using orthogonal incident beam polarizations. In this letter we describe the experimental setup and procedure for this technique, discuss the theoretical foundation for our interpretation scheme, and present experimental results for tensile‐strained GaAsyP1-y‐AlxGa1-xAs and lattice‐matched GaAs‐AlxGa1-xAs quantum‐well structures.   View full abstract»

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  • Photon‐gated photochemical hole burning by two‐color sensitization of a photoreactive polymer via triplet‐triplet energy transfer

    Page(s): 286 - 288
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    A new system of photon‐gated photochemical hole burning is presented: zinc‐tetratolyl‐tetrabenzoporphine in glycidyl azide polymer matrix. The two‐color irradiation with dye laser and Ar+ laser at 20 K forms holes 500 times more efficiently than the one‐color irradiation with dye laser alone. No change in the area of Q‐band in the absorption spectra of the guest molecules during hole formation indicates that the sensitized decomposition of azide groups via triplet‐triplet energy transfer from the higher excited triplet state of the guest molecules causes the change in guest‐host interaction leading to the hole formation. View full abstract»

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  • Whispering‐gallery mode microdisk lasers

    Page(s): 289 - 291
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    A new microlaser design based on the high‐reflectivity whispering‐gallery modes around the edge of a thin semiconductor microdisk is described and initial experimental results are presented. Optical confinement within the thin disk plane results in a microresonator with potential for single‐mode, ultralow threshold lasers. Initial experiments use selective etching techniques in the InP/InGaAsP system to achieve 3–10 μm diameter disks as thin as 500 Å suspended in air or SiO2 on an InP pedestal. Optically pumped InGaAs quantum wells provide sufficient gain when cooled with liquid nitrogen to obtain single‐mode lasing at 1.3 and 1.5 μm wavelengths with threshold pump powers below 100 μW. View full abstract»

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  • Effects of superradiant modes on the performance of free‐electron laser amplifiers

    Page(s): 292 - 294
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    Computer simulation results reveal that the superradiant modes in free‐electron laser amplifiers with high gain and long interaction length tend to degrade the amplifier performance. If these modes are kept at low levels, the amplifier efficiency can be significantly improved. This observation can be employed to interpret the recent MIT reversed guide field free‐electron laser experiment. View full abstract»

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  • Third‐order nonlinear optical response in polymer thin films incorporating porphyrin derivatives

    Page(s): 295 - 297
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    The third‐order nonlinear optical properties of several porphyrin derivatives incorporated in thin films of polymethylmethacrylate have been measured by degenerate four‐wave mixing at 598 nm with 1 ps pulses. Both the magnitude and dynamics of the nonlinear response are measured, with each system exhibiting both a subpicosecond response and a more slowly decaying response (10 ps–1 ns) owing to excited‐state population. A copolymer of silicon phthalocyanine and methyl methacrylate exhibits a fast recovery time (15 ps) and no observable long‐time (∼ns) component of its nonlinear response, as well as an absorption band twice as narrow as that of guest/host samples of the same material. View full abstract»

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  • Size dependence of optical nonlinearity of CdSSe microcrystallites doped in glass

    Page(s): 298 - 300
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    This paper investigates the size dependence of the effective nonlinear cross section σeff and the carrier recombination time on the size of CdS0.12Se0.88 microcrystallites with average radii of 10, 30, 50, and 100 Å by degenerate four‐wave mixing (DFWM) experiments. The decay curves of the DFWM signal as a function of the probe delay time have fast and slow components. As the microcrystallite size decreases, the fast component becomes dominant and a carrier recombination time of 2 ps was observed in the 10‐Å microcrystallites. The diffraction efficiency of DFWM is almost the same for all microcrystallites, that is, σeff has a weak size dependence. Smaller microcrystallites show smaller magnitudes of the third‐order nonlinear susceptibility ∥χ(3)∥, which is calculated from the measured effective nonlinear cross section and the carrier recombination time. View full abstract»

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  • Loss of optical nonlinearity in proton‐exchanged LiNbO3 waveguides

    Page(s): 301 - 303
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    The second‐order optical nonlinearity in a planar waveguide of proton‐exchanged LiNbO3 is directly probed by second‐harmonic generation from 532 to 266 nm in a reflection geometry. Compared to untreated LiNbO3, a 30‐fold reduction in the optical nonlinearity is observed. Contrary to previous reports, we find that the optical nonlinearity cannot be effectively restored by thermal annealing.   View full abstract»

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  • On the linewidth of microcavity lasers

    Page(s): 304 - 306
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    In a recent letter by G. P. Agrawal and G. R. Gray [Appl. Phys. Lett. 59, 399 (1991)] the frequency and phase noise of vertical‐cavity surface‐emitting microlasers is calculated using rate equations and Langevin noise sources. In this letter we re‐examine their calculations and get different results. Specifically, we predict that an increase of the spontaneous emission coupling coefficient will not necessarily lead to an increase in linewidth. It is also found that the reported ‘‘anomalous linewidth enhancement’’ is present in all lasers with a nonzero linewidth enhancement factor. View full abstract»

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  • Pulse fluctuation statistics of an actively mode‐locked external‐cavity semiconductor laser

    Page(s): 307 - 309
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    The pulse amplitude fluctuation statistics of the picosecond pulses generated by active mode locking of an external‐cavity semiconductor laser are measured experimentally. A comparison is made with predictions from a stochastic mode‐locking model, which includes the effects of the spontaneous emission noise and carrier shot noise. Reasonable agreement is obtained for the dependence of the average peak pulse power and the standard deviation of pulse amplitude fluctuations on the bias current.   View full abstract»

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  • Multibeam laser manipulation and fixation of microparticles

    Page(s): 310 - 312
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    A multibeam laser trapping–reaction system was developed to demonstrate independent manipulation of plural microparticles as well as to induce photochemical reaction in a laser‐trapped particle(s). Photopolymerization of vinyl monomers dissolved in a sample solution was employed to fix polystyrene latex particles regularly aligned by laser trapping. Integrated latex structures created by the successive manipulation/polymerization procedures were also shown to be freely manipulated by laser beams. View full abstract»

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  • On the high speed modulation bandwidth of quantum well lasers

    Page(s): 313 - 315
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    A recent formulation of the gain in conventional three‐dimensional double heterostructure (DH) and two‐dimensional quantum well (QW) semiconductor lasers has been used to study the high speed modulation in such lasers. The emphasis is on the differential gain and nonlinear (i.e., intensity dependent) gain suppression in these material systems. We conclude that, in variance with earlier predictions, the expectation of higher modulation speed in QW lasers is not warranted at room temperature. The advantage of using multiple QW structure for high speed performance has been analyzed. View full abstract»

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  • High current back lighted thyratron switch

    Page(s): 316 - 318
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    High current operation of the back lighted thyratron, an optically triggered, low pressure diffuse discharge closing switch that operates with a self heated, super‐emissive cathode, is reported. Repetitive operation at 5 Hz, 17.5 kV, 60 kA, with 500 ns pulse length has been achieved. The switch exhibits no high current limit up to 82 kA. High dI/dt≳1011 A/s and ≪45 ns rise times have been obtained. The high current and short rise time capabilities make this switch a possible replacement for spark gaps and multiple parallel thyratron switches in accelerator and laser applications. View full abstract»

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  • Finite‐element analysis of particle‐particle forces in electrorheological fluids

    Page(s): 319 - 321
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    The first finite‐element analysis of the forces between particles in electrorheological fluids is presented. The shear modulus for chains of particles arrayed on a square lattice is calculated. Two limiting cases are considered: (1) dielectric particles in a dielectric fluid and (2) infinitely conducting particles in an insulating fluid. In (1), the modulus increases linearly with the ratio of dielectric constants Kp/Kf as the ratio becomes large, contrary to expectations from a simple dipole approximation where it would saturate. For case (2), the modulus depends sensitively on the interparticle spacing and diverges when the particles touch. View full abstract»

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  • Aluminum oxide thin films prepared by chemical vapor deposition from aluminum acetylacetonate

    Page(s): 322 - 323
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    Amorphous aluminum oxide thin films were prepared on glass and silicon (100) substrates by a low‐temperature atmospheric‐pressure chemical vapor deposition method. The raw material was aluminum acetylacetonate, which is nontoxic and easy to handle. The substrate temperature could be lowered to 250 °C by the thermal decomposition of aluminum acetylacetonate in air. View full abstract»

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  • Photo‐modulation of light up‐conversion in light transducer using high‐gain photoresponsive amorphous silicon carbide combined with organic electroluminescent diode

    Page(s): 324 - 325
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    Photo‐modulation of light up‐conversion was successfully demonstrated in a new type of light transducer using a high‐gain photoresponsive amorphous silicon carbide (a‐SiC:H) combined with an organic electroluminescent (EL) diode. Green EL output up‐converted from red input‐light was reversibly photo‐modulated by the simultaneously irradiated ultraviolet light due to the effective suppression of photocurrent multiplication in a‐SiC:H film. The present device can be applicable to the logic device for two‐dimensional optical computing. View full abstract»

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  • Si ejection and regrowth during the initial stages of Si(001) oxidation

    Page(s): 326 - 328
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    The initial stages of oxidation of the Si(001)‐2×1 surface have been studied using scanning tunneling microscopy and spectroscopy. Among the new sites generated by the exposure of this surface to O2 are 1.4 Å high bumps on top of the surface. Upon annealing the O2‐exposed surface, or upon O2 exposure at an elevated temperature, these bumps form highly anisotropic islands. Evidence is presented that these bumps and islands are made up of silicon ejected from the surface by the oxidation reaction.   View full abstract»

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  • Chemical vapor deposition of diamond films from water vapor rf‐plasma discharges

    Page(s): 329 - 331
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    Polycrystalline diamond films have been deposited from water vapor rf‐plasma discharges at 1.0 Torr containing various alcohol vapors. No other gases such as H2, F2, or Cl2 were admitted to the growth chamber. Scanning electron microscopy and Raman spectroscopy have been used to characterize the diamond films. In addition, a water‐ethanol mixture has been used for homoepitaxial deposition with a full‐width‐half‐maximum narrower than the bulk substrate (2.60 and 2.75 cm-1, respectively). This technique represents a remarkable new approach to the growth of diamond which does not depend on delivery of hydrogen, fluorine, hydrocarbon, or halocarbon gases that have been typically used by other workers. The nucleation density and topography of the polycrystalline diamond films deposited from the water alcohol mixtures are quite sensitive to the choice of alcohol. Water vapor discharges, by producing H atoms and OH radicals, become the functional equivalent to molecular H2 discharges producing H atoms characteristic of many other diamond chemical vapor deposition techniques. View full abstract»

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  • Optical bistability in ceramic ferroelectrics due to thermal focusing

    Page(s): 332 - 334
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    At modest laser powers (∼1 kW/cm2) ceramic Pb(Mg0.3Nb0.6Ti0.09)O3 exhibits optical bistability. The mechanism is shown to be thermal focusing. At power densities ∼1 kW/cm2 the oscillations between metastable states become nearly periodic (∼8 Hz), in analogy with the behavior exhibited in thermotropic liquid films [M. V. Vasnetsov, JETP Lett. 50, 480 (1990)]. At lower power levels (0.5 kW/cm2) aperiodic switching events are observed with one event per 45 mW (35 W/cm2) of increased laser power, with the Nth switching event occurring at time tN=AN(P-PN)-1, where P is the incident laser power and AN and PN are constants independent of P. The switching events depend also strongly on specimen temperature and its surrounding air pressure. 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