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Applied Physics Letters

Issue 9 • Date Feb 2006

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Displaying Results 1 - 25 of 118
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Collinear dual-color laser emission from a microfluidic dye laser

    Page(s): 091101 - 091101-3
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    Collinear dual-color laser emission on a chip is obtained from a liquid dye mixture flowing through an optical microcavity. Soft lithography has been used to fabricate the microfluidic channels and integrate the optical resonator. The laser cavity, of nanoliter volume, is made of two parallel gold mirrors coated on the end faces of optical fibers and integrated into a polydimethylsiloxane chip. Such a design allows a simple but efficient coupling of the laser emission with an optical fiber. The amplification medium is composed of rhodamine 6G and sulforhodamine, dissolved in a common ethanol solution. When the dye mixture is optically pumped by a pulsed and frequency-doubled Nd:YAG laser, simultaneous laser emission at wavelengths 559 nm and 597 nm is observed, showing yellow and red colors with a complete spatial overlap within the single output beam. Moreover, the overall laser efficiency for the dye mixture system is significantly increased compared to that for the individual dyes. View full abstract»

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  • Defect-mode mirrorless lasing in dye-doped organic/inorganic hybrid one-dimensional photonic crystal

    Page(s): 091102 - 091102-3
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    We have developed a dye-doped organic/inorganic hybrid one-dimensional (1D) photonic crystal containing a dye-doped defect layer for defect-mode photonic band gap lasing. The multilayer laser structure consists of alternating layers of titania nanoparticles and polymethylmethacrylate (PMMA) with an active emission layer of organic dyes in PMMA. Low threshold lasing has been demonstrated at a single defect-mode wavelength of the 1D photonic band gap structure resulting from the inhibited density of states of photons within the stop band and the enhanced rates of spontaneous emission at the localized resonant defect mode. View full abstract»

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  • Generation of femtosecond optical vortices using a single refractive optical element

    Page(s): 091103 - 091103-3
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    It is shown experimentally for small spectral bandwidth that spiral phase plates (SPPs) can generate optical vortices in femtosecond beams without the need for additional dispersion compensation elements. An autocorrelation measurement performed on the obtained optical vortex (OV) beam showed that the SPP did not significantly change the pulse duration. Hence the single element SPP, already an established beam shaping technique in continuous wave and high power regimes, is presented as an efficient and practical means to obtain OVs that are free from spatial chirp in femtosecond beams. View full abstract»

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  • Three-dimensional crystallization inside photosensitive glasses by focused femtosecond laser

    Page(s): 091104 - 091104-3
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    Using scanning electron microscopy, we analyze the laser fluence dependence of three-dimensional crystallized areas induced in bulk photosensitive glass (Foturan) by focused femtosecond laser pulses exposition and subsequent heat treatment. For low fluences (F≪2 J/cm2), the crystallized area is essentially determined by the energy dose distribution above a critical dose. For higher fluences (F≫2 J/cm2), the crystallization length is higher than predicted from the energy distribution due to the filamentation which occurs above a critical fluence Fcrit=1.4±0.3 J/cm2. The filamentation length is found to follow the square root dependence

     F-Fcrit
    . View full abstract»

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  • Laser intensity measurement by Thomson scattering

    Page(s): 091105 - 091105-3
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    We have examined the proposed idea [Ju Gao, Phys. Rev. Lett. 93, 243001 (2004)] of using Thomson scattering to characterize the intensity profile of ultraintense laser fields(≥1018 W/cm2) by calculating the nonlinear Thomson scattering from single and multiple electrons in a Gaussian mode laser field. The results show a close correlation between the spectral features and local laser intensity. The effect may lead to a new scheme of characterizing laser intensity profiles. View full abstract»

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  • Co-planar spin-polarized light-emitting diodes

    Page(s): 091106 - 091106-3
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    Studies of spin manipulation in semiconductors have benefited from the possibility of growing these materials of high quality on top of optically active III–V systems. The induced electroluminescence in these layered semiconductor heterostructures has been used for a reliable spin detection. In semiconductors with strong spin-orbit (SO) interaction, the sensitivity of vertical devices may be insufficient, however, because of the separation of the spin aligner part and the spin detection region by one or more heterointerfaces and because of the short spin coherence length. Here we demonstrate that highly sensitive spin detection can be achieved using a lateral arrangement of the spin polarized and optically active regions. Using our co-planar spin-polarized light-emitting diodes we detect electrical field induced spin generation in a semiconductor heterojunction two-dimensional hole gas. The polarization results from spin asymmetric recombination of injected electrons with strongly SO coupled two-dimensional holes. The possibility of detecting spin polarization of a two-dimensional electron gas (2DEG) induced by the local strayfield of a magnetized Co microstructure deposited on top of the 2DEG close to the co-planar diode junction is also demonstrated. View full abstract»

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  • 1060 nm vertical-external-cavity surface-emitting lasers with an optical-to-optical efficiency of 44% at room temperature

    Page(s): 091107 - 091107-3
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    We report a high power fundamental transverse mode operation of an optically pumped 1060 nm vertical-external-cavity surface-emitting laser. A diamond heat spreader was capillary bonded to the semiconductor surface. A 10 W continuous wave operation with optical-to-optical conversion efficiency of 44% was achieved at room temperature. The thermal rollover was not found up to a heat sink temperature of 60 °C. High efficiency and good thermal stability were mainly due to the optimization of epitaxial quality and the high conductivity of the diamond heat spreader. We have found that the increase of the round trip loss caused by the heat spreader was about 1%. View full abstract»

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  • Tuning emission color of electroluminescence from two organic interfacial exciplexes by modulating the thickness of middle gadolinium complex layer

    Page(s): 091108 - 091108-3
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    Electroluminescent colors of organic light-emitting diodes (OLEDs) can be tuned by modulating the thickness of gadolinium (Gd) complex layer sandwiched between an electron-transporting layer (ETL) and a hole-transporting layer (HTL). The emission colors, which originate from the two interfacial exciplexes simultaneously, can be tuned from green to orange by increasing the thickness of the Gd-complex layer. The atom force microscope images have proved that there are many gaps in the thinner Gd-complex layers. Therefore, besides the exciplex formation between Gd complex and HTL, the exciplex between ETL and HTL is also formed. The results demonstrate that a simple way of color tuning can be realized by inserting a thin layer of color tuning material between HTL with lower ionization potentials and ETL with higher electron affinities. Moreover, photovoltaic device and white OLED based on the two exciplexes are also discussed. View full abstract»

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  • Superprism phenomenon based on holographic polymer dispersed liquid crystal films

    Page(s): 091109 - 091109-3
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    The polarization-dependent superprism phenomenon was demonstrated using holographic polymer-dispersed liquid crystal (HPDLC) films. The HPDLC film is designed and fabricated using three coplanar beams. The fabricated HPDLC film contained two-dimensional ordered nano-sized LC domains (∼150 nm in diameter) embedded in a polymer matrix; its periodicity was estimated to be ∼350 nm. The dispersion of white light from this HPDLC superprism was ∼50°, and the deflection of light output from it was consistent with the theoretical value obtained by the plane wave expansion method. View full abstract»

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  • Effect of fly height and refractive index on the transmission efficiency of near-field optical transducers

    Page(s): 091110 - 091110-3
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    Heat-assisted magnetic recording is a potential remedy to extend the limits of magnetic recording. A high temperature with a steep gradient is used to reduce the local coercivity of the magnetic medium. To achieve such a thermal profile, an intense optical spot well below the diffraction limit is necessary. Transmission efficiency of a near-field optical transducer is affected by various factors at the head-medium interface. Effect of fly height and presence of high refractive index material at the head-medium interface is investigated. Favorable conditions are identified. View full abstract»

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  • Optimum indium composition for (Ga,In)(N,As)/GaAs quantum wells emitting beyond 1.5 μm

    Page(s): 091111 - 091111-3
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    The influence of indium composition and quantum well (QW) thickness on the photoluminescence (PL) properties of high nitrogen content (Ga,In)(N,As)/GaAs QWs grown by molecular beam epitaxy has been investigated in order to get an efficient emission in the 1.5–1.7 μm range. Strong enhancement of room-temperature PL has been observed for postgrowth annealed QWs. However, the optimum annealing temperature depends on the In composition. Taking into account the effects of thermal annealing, a high In content and a very low growth temperature appear to be the best way to obtain an efficient emission beyond 1.5 μm with (Ga,In)(N,As)/GaAs QW. View full abstract»

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  • High power, single-mode operation from photonic-lattice semiconductor lasers with controllable lateral resonance

    Page(s): 091112 - 091112-3
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    An active-photonic-crystal (APC) laser based on laterally resonant arrays of antiguides is proposed and demonstrated. Approximately 1-μm-wide, high-index APC sites are obtained by preferential etching and GaAs regrowth into a GaAs/InGaP/AlGaAs base structure. For 4-μm-wide, low-index APC sites ∼0.28-μm-thick regrowths provide resonant leaky-wave coupling across a 100-μm-wide aperture (i.e., across a 20-element APC structure) at 0.98 μm vacuum wavelength. Large intermodal discrimination favoring in-phase mode operation to high drive levels is obtained at and around the in-phase mode resonance by introducing significant nonsaturatable losses in the high-index sites. The lateral-resonance condition is controlled during fabrication via small variations in the preferential-regrowths thickness on several pieces from the same wafer base. Virtually single-lobe, near-diffraction-limited beam operation is obtained up to 1.1 W peak power at 11 times threshold. This also represents the demonstration of the lateral component needed for the realization of two-dimensional (2D) grating surface-emitting, single-mode APC lasers. View full abstract»

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  • High-power λ∼9.5 μm quantum-cascade lasers operating above room temperature in continuous-wave mode

    Page(s): 091113 - 091113-3
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    We report high-power continuous-wave (cw) operation of λ∼9.5 μm quantum-cascade lasers to a temperature of 318 K. A high-reflectivity-coated 19-μm-wide and 3-mm-long device exhibits cw output powers as high as 150 mW at 288 K and still 22 mW at 318 K. In cw operation at 298 K, a threshold current density of 1.57 kA/cm2, a slope efficiency of 391 mW/A, and a maximum wall-plug efficiency of 0.71% are obtained. In pulsed operation, a maximum average power of 317 mW is achieved at 49% duty cycle. The emission wavelength in cw mode is shifted from 9.524 μm at 288 K to 9.547 μm at 313 K near 1.05 A drive current with a temperature tuning coefficient of 0.92 nm/K. View full abstract»

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  • Single mode photonic crystal vertical cavity lasers

    Page(s): 091114 - 091114-3
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    We report the accuracy of the photonic crystal model in describing the characteristics of vertical cavity surface-emitting lasers with lateral optical confinement consisting of a periodic array of etched circular holes. Experiments were carried out to compare predictions of the photonic crystal model to observed modal device characteristics, and the oxide aperture size was optimized to give maximum output power and lower threshold. The role of loss in improving modal properties was also investigated. Optimized lasers exhibit submilliamp threshold current and operate in the fundamental lateral mode for all currents. View full abstract»

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  • Fabrication of hetero-binary and honeycomb photonic crystals by one-step holographic lithography

    Page(s): 091115 - 091115-3
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    We report the simulation and fabrication of two-dimensional hetero-binary and honeycomb photonic crystals by one-step holographic lithography. These structures are realized by introducing one or three auxiliary beams into the three basic beams forming a regular hexagonal structure. The size contrast between the center rod and its six neighbors in a hetero-binary structure can be tuned by adjusting the intensity contrast between the auxiliary beam and basic beams. The idea of creating heterogeneity into the interference pattern by auxiliary beams could be easily extended to three-dimensional case by adding more beams in the vertical direction. View full abstract»

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  • Polarization characteristics of ZnO rib waveguide random lasers

    Page(s): 091116 - 091116-3
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    Ultraviolet ZnO rib waveguide random lasers with stripe width ranging from 1.7 to 6.5 μm have been fabricated. It is found that the ZnO random lasers demonstrate strong TE lasing emission especially for rib waveguide with a narrower width. Rate equation analysis has shown that the dominant TE lasing emission is due to the corresponding large confinement factor and scattering strength inside the random media with rib waveguide. In addition, Fourier transform studies of the lasing spectra show that the width of rib waveguide constrains the formation of closed-loop paths of lights and, hence, reduces the number of lasing peaks. View full abstract»

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  • Van Hove singularities in intersubband transitions in multiquantum well photodetectors

    Page(s): 091117 - 091117-3
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    Photocurrent spectra of quantum well infrared photodetector (QWIP) devices have been studied over more than three orders of magnitude, revealing features which have been largely overlooked before. Electric field assisted tunneling and, more surprisingly, Van Hove singularities at the miniband edges are shown to play an important role in the low and high energy parts of the QWIP photocurrent spectra, respectively. The photoresponse of QWIPs away from their peak responsivity is found to be non-negligible (≫1% in the 3–5 μm for a 8–12 μm detector), which has to be taken into consideration when optimizing multispectral devices. View full abstract»

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  • Tetrahertz near-field electro-optic probe based on a microresonator

    Page(s): 091118 - 091118-3
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    Electro-optic detection of tetrahertz (THz) pulses typically requires a long nonlinear crystal to accumulate a measurable electro-optic phase shift. The large crystal size prevents application of the method in high-resolution THz near-field microscopy. An electro-optic microresonator that enhances the electro-optic phase shift in a small volume is proposed as a near-field probe for THz microscopy. Frequency response of the microresonator probe is evaluated for different resonator designs. View full abstract»

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  • Mirror that does not change the phase of reflected waves

    Page(s): 091119 - 091119-3
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    We report that electromagnetic wave reflected from a flat metallic mirror superimposed with a planar wavy metallic structure with subwavelength features that resemble “fish scales” reflects like a conventional mirror without diffraction, but shows no phase change with respect to the incident wave. Such unusual behavior resembles a reflection from a hypothetical zero refractive index material, or “magnetic wall”. We also discovered that the structure acts as a local field concentrator and a resonant “amplifier” of losses in the underlying dielectric. View full abstract»

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  • All-solid-state, narrow linewidth, wavelength-agile terahertz-wave generator

    Page(s): 091120 - 091120-3
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    An all-solid-state, narrow linewidth, wavelength-agile THz-wave parametric generator was developed. The THz-wave frequency can be set randomly or tuned rapidly and smoothly over the range from 0.6 to 2.4 THz with a narrow linewidth of 50 MHz. Using this THz-wave parametric generator, accurate and rapid measurements were made of the absorption spectrum of water vapor, with a wide frequency range from 0.8 to 2.1 THz, from a single scan of the THz-wave frequencies. These results demonstrate that this THz-wave parametric generator is a powerful tool with practical applications in THz-wave spectroscopy. View full abstract»

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  • Polarization splitting and terahertz oscillations from a single planar Fabry-Pérot microcavity

    Page(s): 091121 - 091121-3
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    We report the experimental observation of polarization splitting at normal incidence and terahertz oscillations of transmitted light from a single planar microcavity. Optical anisotropy in the SiO2/TiO2-dielectric mirrors leads to two perpendicularly polarized transmission modes. We ascribe the anisotropy to oblique columnar structures in the dielectrics resulting from off-axial growth of the microcavity structure. We apply an up-conversion setup for temporally and spectrally resolved measurements and obtain a corresponding beating of 1.25 THz. Time resolved measurements yield a cavity photon lifetime of 0.65 ps, corresponding to a Q value of 1600. To explain our observations we introduce a Fourier-transform based analytical model. View full abstract»

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  • Quality factor control of Si-based two-dimensional photonic crystals with a Bragg mirror

    Page(s): 091122 - 091122-3
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    We have investigated the coupling between two-dimensional photonic crystals and a distributed Bragg reflector by fabricating silicon-based photonic crystals on top of a one-dimensional Bragg mirror. The two-dimensional photonic crystals contain Ge/Si self-assembled islands as an internal source covering the 1.1–1.6 μm spectral range. We show that we can control the quality factor of Bloch modes by varying the thickness of the silicon layer on top of the Bragg mirror. Quality factors up to 2200 are obtained for optical radiative modes collected from the surface for a photonic crystal with a square lattice pattern. The variation of the quality factor as a function of the thickness of the upper layer is confirmed by three-dimensional finite-difference time domain calculations of the investigated structures. View full abstract»

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  • Increased O(1D) metastable density in highly Ar-diluted oxygen plasmas

    Page(s): 091501 - 091501-3
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    Enhancement of the growth rate of SiO2 with a rare gas diluted O2 plasma is of interest for application to various microelectronics fabrications. The key is the oxygen metastable atom (1D) density, which has the potential for surface activation. We used vacuum ultraviolet optical absorption spectroscopy to detect O(1D) and found a twofold increase in the density of O(1D) due to the dilution with Ar. The density increase is reasonably explained by the increase of the electron density, the oxygen dissociation fraction, and the Ar metastable density, that are experimentally obtained for low O2 fractions. 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