Volume 82, Issue 18, 05 May 2003
- lasers, optics, and optoelectronics
- 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:
- LASERS, OPTICS, AND OPTOELECTRONICS
82(2003); http://dx.doi.org/10.1063/1.1571955View Description Hide Description
We report the fabrication and optical properties of an organic light-emitting microcavity. The cavity is a laser dye-doped polycarbonate film sandwiched between two Bragg reflectors,fabricated by alternately depositing and sol-gel thin films. Reflectivity up to 98% was achieved using the Bragg reflectors. The cavity has a photonic band gap between 597 and 789 nm with a defect state inside the gap. Narrow-band optical pumped light emission from the cavity and its polarization dependence were observed. A cavity quality factor as high as 354 was achieved. Angular and polarization dependence of light emission were analyzed using the transfer matrix method. All experimental results agree well with theoretical calculations.
82(2003); http://dx.doi.org/10.1063/1.1571662View Description Hide Description
We report the development of a tunable laserdiode based on InP using photonic crystalmirrors. The laser consists of two longitudinally coupled ridge waveguide segments that are coupled through a photonic crystalmirror segment. A laterally defined binary superimposed grating provides a distributed feedback in each of the cavities. Quasi-continuous tuning is achieved in a 24.5 nm window with 56 channels as typically required by wavelength division multiplexing applications.
82(2003); http://dx.doi.org/10.1063/1.1571663View Description Hide Description
A normal-mode anisotropicliquid-crystal(LC)gel is demonstrated. In the absence of an electric field, the light polarized along the rubbing direction is scattered. In the voltage-on state, the gel is highly transparent and is independent of polarization. Such a normal modeLCgel exhibits a modest contrast ratio, response time, and low operating voltage. It can be used as a broadband switchable polarizer, variable optical attenuator, and reflective display.
82(2003); http://dx.doi.org/10.1063/1.1572472View Description Hide Description
The electric field recorded in silica samples thermally poled during various intervals was measured by etching. The field is nearly uniform and increases to a maximum in few minutes of poling and subsequently decreases slowly toward a steady level The depletion layer becomes neutral even before the field reaches steady state. An upper limit of was found for the thickness of the negatively charged edge of the depletion region. The value of is the same for all poling times.
Lasing characteristics and modal gain of a lateral-junction InGaAs/GaAs edge-emitting laser diode grown on a patterned GaAs (311) A-oriented substrate82(2003); http://dx.doi.org/10.1063/1.1570925View Description Hide Description
Edge-emitting InGaAs/GaAs laser diodes were grown on patterned GaAs (311)A-oriented substrates. Due to the amphoteric properties of Si as a dopant in high-index GaAs, a device with a lateral junction was obtained. CW lasing was observed up to 200 K. The dependence of the threshold current with temperature was measured. The characteristic temperatures were and for experimental temperatures below and above 100 K, respectively, meaning that the carrier confinement structure must be improved. Quantitative results of the cavity gain were experimentally obtained.
82(2003); http://dx.doi.org/10.1063/1.1571665View Description Hide Description
The two-photon absorption coefficient and Kerr coefficient of bulk crystalline silicon are determined near the telecommunication wavelengths of 1.3 and 1.55 μm using femtosecond pulses and a balanced Z-scan technique. A phase shift sensitivity of the order of 1 mrad is achieved, enabling the accurate measurement of third-order nonlinear coefficients at fluences smaller than From the two-photon absorption coefficient (β∼0.8 cm/GW) and the Kerr coefficient at a wavelength a value for the nonlinear figure of merit for all-optical switching is determined.
82(2003); http://dx.doi.org/10.1063/1.1571977View Description Hide Description
We have demonstrated the operation of a nanophotonic switch that uses three CuCl quantum cubes with a size ratio of 1:√:2. The switching mechanism is based on resonant optical near-field energy transfer between the resonant quantized excitonic energy levels of the quantum cubes. Using near-field optical spectroscopy, we observed a switching rise time of less than 100 ps and a repetition rate of 80 MHz. These results suggest the possibility of making a nanophotonic switching device smaller than 20 nm with a figure of merit 10–100 times higher than that of a conventional photonic switch.
82(2003); http://dx.doi.org/10.1063/1.1571981View Description Hide Description
We describe the fabrication and operation of a device which performs linear optical up-conversion at room temperature. The mechanism for up-conversion is based on internal photoemission from a Schottky contact. We then describe the voltage dependence of this device and interpret it in terms of total energy conservation. Although an AlGaAs/GaAs system is employed here, the functionality is not material-specific and therefore should be widely applicable to different materials systems, such as GaN/InGaN.
82(2003); http://dx.doi.org/10.1063/1.1572966View Description Hide Description
We propose a scheme for mode selection in a square-shaped two-dimensional layered microcavity laser. By using a fused-silica square-shaped capillary containing a dye-doped liquid as a layered microcavity, whose refractive index was smaller than that of the fused silica, we could realize our idea for single spatial-mode lasing. By analyzing the amount of peak shift induced by varying the refractive index of inner liquid, we could confirm that the lasing modes originate by the free-running trajectories that are constrained on the outer layer by the presence of the inner boundary in such a way that only the ray having a refraction angle of in the inner gain layer could be selected.
82(2003); http://dx.doi.org/10.1063/1.1572962View Description Hide Description
Nonlinear optical (NLO) polymer is proposed as one of the best candidates for nonlinear photonic crystal(PC)waveguides. A dry etching technique for this material is established at the suboptical wavelength scale needed to fabricate NLO polymerPCwaveguides, with the good processability achieved in this material demonstrated by the successful fabrication of a PCwaveguide in NLO polymer. Sharp resonances originating from coupling to photonic band modes are observed in the optical reflectance spectra of this waveguide, with resonant frequencies found to depend on the angle and in-plane propagation lattice direction of incident light.
Stacking and translation of microscopic particles by means of beams emitted from a vertical-cavity surface-emitting laser array82(2003); http://dx.doi.org/10.1063/1.1570939View Description Hide Description
We report on an optical manipulation method to achieve stacking of multiple particles by simultaneous emission of vertical-cavity surface-emitting lasersources. In the experiment, up to seven polystyrene particles of 10-μm diameter were stacked vertically by illuminating beams. Furthermore, we could translate the particles keeping the stacked state without mechanical movement. The maximum number of stackable particles was obtained when the focal spots of the beams were located 20 μm above the sample stage. We also found that the relation between the spot pitch and the particle diameter is an important factor to achieve stacking. This manipulation method is expected to be useful for microfabrication of a three-dimensional structure and collective translation of materials capsuled in microparticles.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
82(2003); http://dx.doi.org/10.1063/1.1569989View Description Hide Description
Impurity-induced modes at 212 and have been studied by using Raman scatteringspectroscopy in Be-doped cubic boron nitride single crystals, which have been grown by the temperature-gradient method under high pressure. Those bands show prominent polarizationproperties of and modes for the 212 and bands, respectively. Based on the polarizationproperties and a simple calculation of a molecular model, the origin of the bands is explained by postulating resonance modes of substitutional Be with a weak force constant between the host atoms and the Be. Anomalies of a forbidden transverse optical mode and the mode due to phonon–plasma coupling caused by photoexcited free carriers have been also observed in high excitation density.
White light emission from radical carbonyl-terminations in porous glasses with high luminescence quantum efficiencies82(2003); http://dx.doi.org/10.1063/1.1569038View Description Hide Description
Development of white phosphors with highly emissive, stable, and less toxic characteristics has been important for display and lighting technology. In this letter, it is shown that sol-gel-derived glasses of aluminosilicate composition, followed by a heat treatment in air at low temperatures around 500 °C, exhibit two intense, visible photoluminescence bands: One is due to point defects in these glasses and the other comes from radical carbonyl-terminations on the surface of pores. The photoluminescence provides a white light with high luminescencequantum efficiency (∼66.5%) under long-wavelength ultraviolet excitation.
82(2003); http://dx.doi.org/10.1063/1.1572478View Description Hide Description
We report effusive evaporation of thin films on GaAs(001) substrates in a production-type molecular-beam epitaxy system. A polycrystalline charge heated in a high-temperature effusion cell is used as the evaporation source. The structures are characterized by atomic force microscopy(AFM),Rutherford backscatteringspectroscopy(RBS), ellipsometry, and transmission electron microscopy(TEM). The films are amorphous and stoichiometric by transmission electron diffraction and RBS, respectively. Under optimal growth conditions, the film surface has a typical roughness of 2–3 Å as revealed by AFM, while the interface is atomically abrupt as confirmed by the cross-sectional TEM. Such amorphous and stoichiometric oxide paves the way for GaAs gate dielectrics applications.
Identification of hexagonal polycrystal in epitaxially grown InN by synchrotron x-ray diffraction and near-edge x-ray absorption fine structure spectroscopy82(2003); http://dx.doi.org/10.1063/1.1572475View Description Hide Description
The structures and crystallographic orientations of indium nitride films of varying thicknesses on sapphire(0001) were investigated using high-resolution synchrotron x-ray scattering and angle-dependent near-edge x-ray absorption fine structure(NEXAFS)spectroscopy with linearly polarized rays. The x-ray scattering data showed that epitaxially grown InN films have a polycrystallinestructure when their thickness is greater than 3000 Å. The NEXAFS spectra of thin films have a strong polarization-dependent spectral feature resulting from the preferred c-axis orientation. This polarization dependence decreases as the film thickness increases and is not present in the spectra of films that are more than 3000 Å thick. These results indicate that the axis has a preferred orientation in thin films, but that this orientation is random in thick films, which have a polycrystalline hexagonal structure.
82(2003); http://dx.doi.org/10.1063/1.1571984View Description Hide Description
Critical cooling rate of a metallic liquid necessary to form glass is correlated to the valence concentration of the liquid and denote valence and atom number in a unit cell, respectively). of liquid is minimized at The principles of the composition design to form bulk metallic glasses are as follows: the component number in the alloy is larger than three, and the component percentage of the component approaches
82(2003); http://dx.doi.org/10.1063/1.1572469View Description Hide Description
Carrier lifetime measurements have been used to characterize residual defects after low-energy implanting of silicon ions followed by high-temperature annealing (900 or 1000 °C). The implant was found to result in two distinct regions of lifetime-reducing damage. First, a high recombination region, most likely due to stable dislocation loops, remained near the surface. In addition, deeply propagated defects, which were not present prior to annealing, were also detected. These deep defects, which are possibly siliconinterstitials, diffuse so rapidly during annealing that their distribution becomes effectively uniform to a depth of 100 microns. Annealing at higher temperatures was found to reduce the severity of both the surface and the deeply propagated defects.
Influence of MgO substrate miscut on domain structure of pulsed laser deposited as characterized by x-ray diffraction and spectroscopic ellipsometry82(2003); http://dx.doi.org/10.1063/1.1572464View Description Hide Description
Pulsed laser deposition has been used to grow highly oriented on (001)MgO and miscut MgO off 001 toward 100) in the presence of a pulsed jet. The target stoichiometry was but filmsgrown at were cation deficient and had a final composition of Visually, the films were specular, but spectroscopicellipsometry measurements showed they were highly absorbing, requiring a short anneal in at to make them fully transparent. Pole figure analysis indicated that a thick film consisted of the characteristic antiphase domain structure of SBN, but four antiphase domains were found in a thin film. However, the formation of these additional domains was suppressed in a filmgrown on miscut MgO. Spectroscopicellipsometry measurements have been made to measure surface and interface roughness, film thickness, as well as the spectroscopic refractive index and extinction coefficient of the films.
82(2003); http://dx.doi.org/10.1063/1.1569052View Description Hide Description
The dielectric function of nanocrystallinesilicon (nc-Si) with crystallite size in the range of 1 to 3 nm has been determined by spectroscopic ellipsometry in the range of 1.5 to 5.5 eV. A Tauc–Lorentz parameterization is used to model the nc-Si optical properties. The nc-Si dielectric function can be used to analyze nondestructively nc-Si thin films where nanocrystallites cannot be detected by x-ray diffraction and Raman spectroscopy.
82(2003); http://dx.doi.org/10.1063/1.1572473View Description Hide Description
Due to its indirect bandstructure, bulk crystalline silicon is generally regarded as a poor light emitter. In contrast to this common perception, we report here on surprisingly large external photoluminescencequantum efficiencies of textured bulk crystalline silicon wafers of up to 10.2% at and of 6.1% at room temperature. Using a theoretical model to calculate the escape probability for internally generated photons, we can conclude from these experimental figures that the radiative recombination probability or internal luminescencequantum efficiency exceeds 20% at room temperature.