Volume 88, Issue 25, 19 June 2006
- 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
- interdisciplinary and general physics
Index of content:
We demonstrate theoretically the simultaneous localization of photons and phonons in the same spatial region by introducing lattice defects in a periodic array of dielectric/elastic material that exhibits gaps for both electromagnetic and elastic waves. Transverse electromagnetic waves, pure shear elastic waves, and mixed shear and dilatation elastic waves were simultaneously localized. The coexistent localization of light and sound can have a strong influence on photon-phonon interactions (i.e., optical cooling) and the possibility of dual acoustic-optical devices that can integrate the management of sound, heat, and light.
- LASERS, OPTICS, AND OPTOELECTRONICS
88(2006); http://dx.doi.org/10.1063/1.2213958View Description Hide Description
There is a wide interest in single-mode optical fibers for the middle infrared range of . These fibers will be useful for a variety of applications such as spatial filtering and interferometry. However, many technical and theoretical problems hindered the development of such fibers. Segmented cladding fibers may make it possible to combine an extremely large core area and single mode operation over a large spectral range. The design parameters may accurately control the optical properties of such fibers. We report here the design and fabrication of segmented cladding fibers made of crystalline silver halides, which are highly transparent in the middle infrared.
88(2006); http://dx.doi.org/10.1063/1.2215602View Description Hide Description
The crystal quality of quantum dots(QDs) is substantially improved without redistribution of composition using inductively coupled Ar plasma exposure. After plasma exposure, the QDs exhibit an increase in photoluminescence intensity by a factor of 1.7 while keeping the peak wavelength unshifted, and the band gap blueshift after rapid thermal annealing is suppressed, denoting an improvement in thermal stability. The time-resolved photoluminescence shows an increase in carrier lifetime from by plasma exposure, indicating the mechanism of grown-indefects reduction in the QD regions.
88(2006); http://dx.doi.org/10.1063/1.2216353View Description Hide Description
(002) oriented AlNthin films with a columnar microstructure fabricated by vapor phase deposition with a sample bias exhibit excellent field emissionproperties. The field emissioncurrent density increases with smaller film thickness, and at a thickness of , the current density reaches and the turn-on field is close to . Atomic force microscopy discloses nanoscale protrusions on the surface that greatly expand the emission area and efficiency. The Fowler-Nordheim plot reveals a linear dependence under low electric field, suggesting that the emission current originates from the quantum tunneling effect.
88(2006); http://dx.doi.org/10.1063/1.2216871View Description Hide Description
We experimentally demonstrate a single-beam holography for creating Agnanoparticle-embedded eight-fold quasicrystals. By adjusting the phase relation of interference beams through an optical mask, we obtain eight-fold symmetry structures with three different profiles. The structure of quasicrystals is confirmed through scanning electron microscopy and optical diffraction pattern, respectively. Furthermore, we also numerically demonstrate that the method can encode even higher symmetric structures such as the most complex 14- and 18-fold quasicrystals as well by computer simulations.
88(2006); http://dx.doi.org/10.1063/1.2216888View Description Hide Description
We investigate an optically induced distributed-feedback cavity, containing a densely packed luminescent siliconnanocrystal layer in a based matrix as active medium. In the presence of optical feedback, we have observed a nonlinear increase in the spectrally resolved emission intensity on the blue emission wing, which consists of two main contributions: (i) a broad amplified region around , showing fast photoluminescence decay around , depending on the excitation intensity, and (ii) a narrower peak located at about . The latter exhibits a spectral shift, which varies with the cavity tuning.
88(2006); http://dx.doi.org/10.1063/1.2216903View Description Hide Description
Porous chiralthin films composed of a nearly hexagonal-close-packed array of helical nanorods of tris-(8-hydroxyquinoline) aluminum are fabricated using glancing angle deposition and exhibit a one-dimensional polarization-dependent photonic stop band. These chiralthin films transmit only one handedness of circularly polarized light and emit highly circularly polarized photoluminescence. The strong circular Bragg phenomena exhibited by these films suggest potential for use of these films in low-threshold mirrorless lasing and circularly polarized emission applications, while the porosity of the films allows for infiltration by dyes or liquid crystals to enable the formation of unique hybrid materials.
88(2006); http://dx.doi.org/10.1063/1.2216920View Description Hide Description
A theoretical investigation is performed in order to understand the origin of change of the operating wavelength of quantum dots-in-a-wellphotodetectors when the well width is varied. The energy levels and wave functions were found using the eight-band strain dependent model and the intraband optical absorptionspectrum was calculated in the dipole approximation within the framework of first order perturbation theory. It was found that the pure effect of changes of well width cannot be responsible for the shifts of the peaks observed in experiment [Raghavan et al., J. Appl. Phys.96, 1036 (2004)], which are therefore ascribed to unintentional changes in dot dimensions.
88(2006); http://dx.doi.org/10.1063/1.2214143View Description Hide Description
We report a detailed study of distortion effects in electro-optical sampling measurement at near-zero optical bias. It is found that when the induced optical retardation has a dynamic range larger than the optical bias, a false polarity change of the field can be observed merely due to the amplitude change of the field under investigation. The distortion cannot be corrected in general. However, when the optical bias is known, this phenomenon can be exploited to derive the absolute field amplitude under study.
Dependence of saturation effects on electron confinement and injector doping in quantum-cascade lasers88(2006); http://dx.doi.org/10.1063/1.2214128View Description Hide Description
We report on a detailed experimental and theoretical analysis of the role of injector doping density on both the threshold current density and the saturationcurrent density, determining the dynamic range of the quantum cascade lasers. The experimental results were obtained from two growth series of quantum-cascade lasers based on single and double phonon resonance depopulation mechanisms. We derive a quasilinear dependence of on the injector doping density of both designs for doping range as wide as . Despite threshold current increase the faster rise of saturationcurrent with doping results in an enhanced dynamic range for injector doping up to . For higher doping levels, itself saturates. Furthermore, our investigations yield that single phonon resonance devices exhibit clear currentsaturation simultaneously with a decrease of the optical power, whereas two phonon resonance devices show only power saturation, which we attribute to increased leakage currents. These deteriorate the laser performance of the latter design at higher operational temperatures.
Efficient white-light-emitting diodes based on poly(-vinylcarbazole) doped with blue fluorescent and orange phosphorescent materials88(2006); http://dx.doi.org/10.1063/1.2214141View Description Hide Description
We have fabricated polymer white-light-emitting devices possessing a single emitting layer containing a hole-transporting host polymer, poly(-vinylcarbazole), and an electron-transporting auxiliary, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, doped with a blue-light-emitting amino-substituted distyrylarylene fluorescent dye and an orange-light-emitting osmium phosphor. The doubly doped device exhibited an intense white emission having Commission Internationale de l’Eclairage coordinates of (0.33, 0.34), a high external quantum efficiency of 6.12% , and a maximum brightness of . The color coordinates remained unchanged over a range of operating voltages, even at luminance as high as .
88(2006); http://dx.doi.org/10.1063/1.2214146View Description Hide Description
Zinc oxide nanodonuts have been synthesized using vapor-phase transport method. Zinc oxide powder, graphite powder, and erbium oxide powder were mixed with a molar ratio of 1:1:0.2 and heated at in a flowing argon environment. Perfectly donut-shaped nanostructures with outer diameters ranging from were observed. The inner diameter of the zinc oxide donut varies from and the vertical distance from the highest point to the lowest point vary from . The composition of the nanodonut was analyzed using Auger electron spectroscopy and was found to be mainly of zinc oxide. Diffusion of silicon into the zinc oxide layer was confirmed by secondary ion mass spectroscopy.
88(2006); http://dx.doi.org/10.1063/1.2216402View Description Hide Description
Fluctuations of the white-light supercontinuum produced by ultrashort laser pulses in self-guided filaments (spatiotemporal solitons) in air are investigated. We demonstrate that correlations exist within the white-light supercontinuum, and that they can be used to significantly reduce the laser intensity noise by filtering the spectrum. More precisely, the fundamental wavelength is anticorrelated with the wings of the continuum, while conjugated wavelength pairs on both sides of the continuum are strongly correlated. Spectral filtering of the continuum reduces the laser intensity noise by , showing that fluctuations are rejected to the edges of the spectrum.
88(2006); http://dx.doi.org/10.1063/1.2214176View Description Hide Description
We report on the design, fabrication, electro-optical performance, and stability of switchable polarizationgratings formed in azo-dye-doped nematic liquid crystals. Stable gratings are demonstrated even after applying saturating electric fields and after heating to extreme temperatures . A simple phenomenological model is presented to show that the Freedericksz threshold voltage depends on surface and volume contributions. The observed thresholdless behavior indicates that the grating stability is consistent with a surface-stabilizing effect.
Strong enhancement of emission at room temperature in silicon-on-insulator photonic crystal waveguides88(2006); http://dx.doi.org/10.1063/1.2214180View Description Hide Description
We have realized silicon-on-insulator photonic crystal(PhC)waveguides with intense emission at room temperature. The slabs contain a thin layer of with dopedsiliconnanoclusters embedded at the center of the Si core and are patterned with a triangular lattice of holes. An enhancement by more than two orders of magnitude of the near-normal emission is observed when the transition is in resonance with an appropriate mode of the PhC slab. The results are in very good agreement with calculated photonic bands and emission spectra. These findings are important for the realization of Si-compatible efficient light emitters at telecom wavelengths.
88(2006); http://dx.doi.org/10.1063/1.2215610View Description Hide Description
In this letter, a type of guided-mode resonance (GMR) reflection filter incorporating multimode resonance and the Brewster effect is presented. Long-range, low sidebands, and multiple channels are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. Detailed characteristics are calculated using rigorous coupled-wave analysis. In our calculation, for TM-polarized incident wave, we find it sufficiently accurate to calculate the effect index by using the zero-order permittivity of the effective media theory, and narrowband multichannel reflectance can be achieved at the Brewster angle by tuning the grating depth.
88(2006); http://dx.doi.org/10.1063/1.2215618View Description Hide Description
N-doped and In-N-codoped ZnOfilms were fabricated on quartz glass substrate by sol-gel spin coating. Their -type conductivities were characterized by the Hall measurements, revealing low resistivities of the order of . Thin-film junctions comprising an undoped ZnO layer and a N-doped ZnO layer displayed the typical rectifying characteristics, suggesting formation of homojunctions at the interfaces.
Tunable watt-level blue-green vertical-external-cavity surface-emitting lasers by intracavity frequency doubling88(2006); http://dx.doi.org/10.1063/1.2215635View Description Hide Description
We report on the development and the demonstration of a tunable, watt-level, blue-green, linearly polarized vertical-external-cavity surface-emitting lasers operating around by intracavity second-harmonic generation. By using lithium triborate crystal, we have achieved over continuous wave blue-green power at with a tunability.
88(2006); http://dx.doi.org/10.1063/1.2216024View Description Hide Description
Temperature dependent characteristics of quantum-cascade lasers (QCLs) operating up to in continuous-wave (cw) mode are reported. A high-reflectivity coated-wide and -long epilayer-down bonded QCL using a diamond submount shows a considerable improved cw operation with an output power of and a threshold current density of at . The temperature dependence on optical and electrical performances of the QCLs with respect to the output power, slope efficiency, threshold current/voltage, turn-on voltage, differential series resistance, and emission wavelength are investigated systematically above liquid nitrogen temperature.
88(2006); http://dx.doi.org/10.1063/1.2216026View Description Hide Description
We demonstrate enhanced terahertz detection using photoconductive antennas based on self-assembled ErAs:GaAs nanoisland superlattices. Three detectors are compared; one each fabricated on low-temperature grown GaAs, radiation-damaged silicon-on-sapphire, and an ErAs:GaAs superlattice. The ErAs:GaAs based detector shows a strong enhancement in terahertz detection efficiency with respect to incident optical power, though optical saturation occurs more rapidly. Detected terahertz bandwidth and signal-to-noise ratios are simultaneously maintained or improved.
Terahertz pulse propagation using plasmon-polariton-like surface modes on structured conductive surfaces88(2006); http://dx.doi.org/10.1063/1.2216105View Description Hide Description
The dispersion relation and confinement of plasmon-polariton-like terahertz surface modes sustained by a perfectly conducting planar surfacepatterned with a regular lattice of holes are studied using full-field three-dimensional numerical simulations. Edge coupling and subsequent surface guiding with subwavelength vertical confinement of the frequency components below the band edge of the surface mode is demonstrated for a broadband pulse with . Additionally, the constraints imposed by lattice constant and hole size on the creation of defect waveguides offering lateral confinement are discussed.