Volume 85, Issue 20, 15 November 2004
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Data are presented demonstrating the laser operation (quasicontinuous, ) of an InGaP–GaAs–InGaAs heterojunction bipolar light-emitting transistor with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the -type base region. Besides the usual spectral narrowing and mode development occurring at laser threshold, the transistor current gain in common emitter operation decreases sharply at laser threshold .
- LASERS, OPTICS, AND OPTOELECTRONICS
85(2004); http://dx.doi.org/10.1063/1.1826224View Description Hide Description
A photorefractive polymercomposite sensitized at 1550 nm through direct two-photon absorption has been developed. We show an external diffraction efficiency of 3% in four-wave-mixing experiments and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymercomposite. Amongst other potential applications, the demonstration of accurate, dynamic aberration correction through holography in this all-organic photorefractive device presents an alternative to complex adaptive optics systems currently employed in through-air optical communication links.
85(2004); http://dx.doi.org/10.1063/1.1823595View Description Hide Description
Measured spatial variations of field phase and amplitude versus position inside a wire/split ring resonator negative refractive index metamaterial are presented that show that the phase velocity inside a negative index material points toward the source and consequently that phase velocity and energy flow are reversed in such a medium. These measurements directly demonstrate the fundamental behavior of electromagnetic waves in a negative refractive index material. The same internal field measurements are also used to accurately and reliably measure the effective bulk properties of the negative index metamaterial.
Time- and spectrally resolved ultrafast gain dynamics of a semiconductor optical amplifier under phase-correlated multiwavelength pulse amplification85(2004); http://dx.doi.org/10.1063/1.1823037View Description Hide Description
The ultrafast gain dynamics of an AlGaAs semiconductor optical amplifier (SOA) are measured under phase-correlated multiwavelength pulse amplification using time-resolved pump–probe techniques. Both the temporal and spectral gain dynamics are measured. Carrier heating due to two photon absorption, carrier cooling, four-wave mixing, and cross-phase modulation effects are observed. These effects are evident when amplifying dispersion compensated pulses, and it is shown how these effects decrease when amplifying nondispersion compensated (chirped) pulses. This helps to avoid nonlinear effects in the gain media (SOA), which, in turn, helps to support the operation of external cavity multiwavelength semiconductormode-locked lasers where the intracavity pulses are inherently chirped.
85(2004); http://dx.doi.org/10.1063/1.1815371View Description Hide Description
Electron and hole relaxation kinetics are studied in modulation-doped InAsquantum dots using femtosecond time-resolved photoluminescence experiments. We demonstrate that, as a result of doping,carrier relaxation from the barrier layers to the quantum dotground states is strongly enhanced due to rapid electron–hole scattering involving the built-in carrier population. Results for -doped quantum dots reveal a threefold decrease in the room-temperature electron relaxation time relative to corresponding undoped quantum dots. Our findings are promising for the development of high-speed, GaAs-based quantum dot lasers with modulation speeds in excess of .
Room-temperature, mid-infrared electroluminescence from single-stage intersubband -based edge emitters85(2004); http://dx.doi.org/10.1063/1.1819518View Description Hide Description
-based, single-stage, intersubband devices with active regions composed of deep quantum wells (i.e., ) and high barriers display strong room-temperature emission at . The structures are grown by metalorganic chemical vapor deposition. The large energy barriers for electrons in the upper energy level of the active region strongly suppress both the carrier leakage as well as the tunneling escape rate out of the wells. As a result, the ratio of emissions at 80 and is as low as 2.0, and thus there is considerably less need for a Bragg mirror/transmitter-type region. Devices with virtually 100% tunneling injection efficiency have been realized, and their room-temperature spectra are narrow: full width at half maximum. These deep-well, single-stage structures are intended for use as the emitting units in two-dimensional, intersubband quantum-box lasers, or as the stages of quantum-cascade lasers for efficient, room-temperature operation in the wavelength range.
85(2004); http://dx.doi.org/10.1063/1.1813643View Description Hide Description
We study polymer light-emitting diodes with a homojunction, i.e., junction between two layers with the same host material. One layer is poly (9,9-dioctylfluorene-2,7-diyl) (PFO) host blended with a small amount of poly (2-methoxy-5 (2'-ethyl-hexyloxy)-1,4-phenylene vinylene), another layer is either pure PFO or PFO host blended with green-emitting polyfluorene copolymers. Such homojunction devices are solution processed and show efficient white light emission. The peak luminance is reached at with Internationale de L’Eclairage (CIE) coordinate (0.34, 0.34).
85(2004); http://dx.doi.org/10.1063/1.1823594View Description Hide Description
We report theory and experiment on ultrahigh-order modes in a symmetrical metal-cladding thick optical waveguide. The waveguide consists of a slab or a glass slab with a thickness greater than , two goldfilmsdeposited on the upper and bottom sides of the slab serving as the cladding of the waveguide. By using the free-space coupling technique, ultrahigh-order modes are excited, and its high sensitivity to both refractive index and thickness of the guide, as well as the polarization independence are demonstrated.
85(2004); http://dx.doi.org/10.1063/1.1823013View Description Hide Description
Self-organized spontaneous gratings were induced on a surface of azobenzene polymer by an irradiation of frequency doubled neodymium doped yttrium–aluminum–garnet pulsed laser.Irradiation of uniform single laser beam at normal incidence induced periodic line shaped structures on a polymer surface. The structure is so-called laser induced periodic surface structure (LIPSS) which was formed along the direction parallel to the polarization direction of pulsed laser. The LIPSS was formed above the critical thickness around . Irradiation of -polarized holographic interference beams induced the distinguished holographicsurface relief grating (SRG) structures.Irradiation of -polarized holographic interference beams induced egg crate-like (ECL) structures. A combination of holographic SRG and sequential LIPSS is the likely cause of the ECL patterns observed in this work.
85(2004); http://dx.doi.org/10.1063/1.1823036View Description Hide Description
By coupled mode theory in the time domain and a finite-difference time-domain code, we investigate wavelength shifting and frequency conversion via four-wave mixing inside a photonic crystal wire in an isotropic Kerrmaterial. The three-dimensional time-resolved analysis yields ultrafast and all-optically tunable frequency conversion of a signal/channel about the pump frequency.
85(2004); http://dx.doi.org/10.1063/1.1821630View Description Hide Description
Rare-earth-based lasing action in GaN is demonstrated. Room-temperature stimulated emission (SE) was obtained at 620 nm from an optical cavity formed by growingin situ Eu-doped GaN thin films on sapphire substrates. The SE threshold for optical pumping of a at. % Eu-doped GaN sample was . The SE threshold was accompanied by reductions in the emission linewidth and lifetime. A modal gain of and a modal loss of were obtained.
85(2004); http://dx.doi.org/10.1063/1.1823035View Description Hide Description
We report transmission and reflection characteristics of in-plane hetero-photonic crystals (IP-HPCs) consisting of two serially connected photonic crystal waveguides with differing lattice constants. We show experimentally and theoretically that the transmission spectrum of the structure corresponds to the transmission frequency range common to both waveguides. Also, there exists a frequency gap where the structure has a guiding mode for one waveguide but not for the neighboring one. Our calculated results reveal that light within the common frequency range is transmitted with approximately 100% efficiency through the waveguides while light within the gap is almost perfectly reflected.
Optimization of ridge height for the fabrication of high performance ridge waveguide lasers with pulsed anodic oxidation85(2004); http://dx.doi.org/10.1063/1.1824180View Description Hide Description
The dependence of the ridge height on the performance of the ridge waveguide (RWG) lasers has been systematically studied. It was found that the optimum ridge height corresponds to an etching depth where all the -doped layers above the active region were removed. triple-quantum-well RWG lasers with optimized ridge height were fabricated with pulsed anodic oxidation. The lowest threshold current density of was obtained from a RWG laser. The corresponding transparency current density of the fabricated RWG lasers was (equivalent to per well).
Polarity reversal of the magnetic field induced component of terahertz radiation from surfaces at high density excitation85(2004); http://dx.doi.org/10.1063/1.1814815View Description Hide Description
The excitation density dependence of radiation power and wave forms of the terahertz wave from surface under magnetic fields was investigated. A drastic change of the wave forms was observed at high density excitation and was explained by the polarity reversal of the terahertz wave form induced by the magnetic field. The reversal originates from the crossover of the radiation mechanism of the magnetic induced component from the electrons in the accumulation layer to the diffusion current by the photogenerated electrons at high-density excitation under a magnetic field.
85(2004); http://dx.doi.org/10.1063/1.1818740View Description Hide Description
We show that supercontinuum generation in a fiber containing a Bragg grating exhibits enhancement near the Bragg resonance wavelength. We also show that the gratingdispersion exceeds the waveguidedispersion over a bandwidth far in excess of its photonic band gap. The observed enhancement is consistent with nonlinear Schrödinger equation simulations of the supercontinuum formation that combine grating and waveguidedispersion.
Optical and electro-optical properties of submicrometer lithium niobate slab waveguides prepared by crystal ion slicing and wafer bonding85(2004); http://dx.doi.org/10.1063/1.1819527View Description Hide Description
thin film crystals have been produced using crystal ion slicing and wafer bonding. Films with a thickness of are produced on a thin layer of , which is deposited on a substrate with electrodes. The crystalline and optical qualities of the fabricated thin films are investigated and are comparable to bulk single crystals. The effect of thermal annealing is studied using Rutherford backscattering. The refractive indices and the electro-optical (EO) coefficient of the fabricated films are measured using prism coupling dark line spectroscopy and modified attenuated total reflection. The EO coefficient is equal to at .
Ultrafast nonresonant third-order optical nonlinearities in ZnSe for photonic switching at telecom wavelengths85(2004); http://dx.doi.org/10.1063/1.1823599View Description Hide Description
We report the steady-state and time-resolved z-scan measurements of the nonresonant third-order optical nonlinearities in ZnSe at telecom wavelengths. The measurements demonstrate that ZnSe could be used for ultrafast all-optical switching at 1310 and .
White organic light-emitting diodes based on 2,7-bis(2,2-diphenylvinyl)-9,-spirobifluorene: Improvement in operational lifetime85(2004); http://dx.doi.org/10.1063/1.1824178View Description Hide Description
Very bright white organic light-emitting diodes were fabricated using 2,7-bis(2,2-diphenylvinyl)-9,-spirobifluorene (DPVSBF) doped with [4-(dicyanomethylene)-2--butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)--pyran)] (DCJTB) as the emission layer. With a device configuration of , a brightness of with an external quantum efficiency of 3.31% and luminous efficiency of , a power efficiency of was achieved at a driving current of . The brightness reached at . The Commission Internationale de l’Eclairage coordinates stayed nearly constant, changed from (0.35, 0.36) to (0.32, 0.34) when the voltage increased from . The relative operational lifetime of the device increased by a factor of compared with a similar device based on 4,-bis-(2,2-diphenylvinyl)-1,-biphenyl as the source of the blue emission. The much extended half-lifetime was attributed to the higher morphological stability of the DPVSBF.
Terahertz generation by difference-frequency mixing of exciton Wannier–Stark ladder states in biased semiconductor superlattices85(2004); http://dx.doi.org/10.1063/1.1819508View Description Hide Description
We report the generation of terahertz (THz) radiation in a biased semiconductorsuperlattice by difference-frequency mixing of interband transitions. The Wannier–Stark spectrum of the superlattice was selectively excited by two spectrally narrow laser lines. The emitted THz radiation was measured as a function of the energetic splitting and spectral position of the bichromatic excitation. The generation of tunable THz radiation is verified. The results clearly show enhanced THz emission when either continuum or excitonwave packets are excited. Good agreement is obtained between the experiment and the results of an exciton model of the nonlinear coherent dynamics.
Low-voltage, polarization-insensitive, electro-optic modulator based on a polydomain barium titanate thin film85(2004); http://dx.doi.org/10.1063/1.1819515View Description Hide Description
A thin-film electro-optic waveguide modulator with a half-wave voltage-interaction length product of at wavelength is demonstrated. The half-wave voltage and the measured effective electro-optic coefficient are and , respectively. The half-wave voltage increases less than 10% over a temperature range of . Polarization-independent electro-optic modulation was observed and attributed to the polydomain structure of the film. The unique combination of large electro-optic coefficient and polarization independence illustrates how engineered domain structures in ferroelectric thin films can enable properties and performance unachievable in bulk single crystals.
- PLASMAS AND ELECTRICAL DISCHARGES
85(2004); http://dx.doi.org/10.1063/1.1812367View Description Hide Description
A combined electron- and ion-beam system employing a double-chamber plasma source and a single accelerator column has been developed to provide focused electron and positive-ion beams simultaneously, with no need for a separate electron source or accelerating column for sample neutralization. The self-aligned ion and electron beams can be used to micromachine and image a variety of materials, both conducting and insulating. Together with an ion-beam imprinting scheme, the combined electron/ion beam system is compact and provides low-cost, high-throughput, and large-area micromachining.