Volume 88, Issue 7, 13 February 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
- applied biophysics
- interdisciplinary and general physics
Index of content:
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The shifts of ferroelectric phase transition temperatures and domain stabilities of thin films as a function of strain and temperature were studied using phase-field simulations. A new Landau-Devonshire thermodynamic potential based on an eighth-order polynomial was employed for describing the bulk free energy of single crystals, which allows the exploration of domain stability in the full range of experimentally accessible compressive and tensile strains. Based on the simulation results, a phase diagram was constructed, which displays the stability of various ferroelectric phases and domain structures as a function of temperature and strain.
- LASERS, OPTICS, AND OPTOELECTRONICS
Resonantly-enhanced transmission through a periodic array of subwavelength apertures in heavily-doped conducting polymer films88(2006); http://dx.doi.org/10.1063/1.2175482View Description Hide Description
We observed resonantly-enhanced terahertz transmission through two-dimensional (2D) periodic arrays of subwavelength apertures with various periodicities fabricated on metallic organic conducting polymerfilms of polypyrrole heavily doped with molecules . The “anomalous transmission” spectra are in good agreement with a model involving surface plasmonpolariton excitations on the filmsurfaces. We also found that the ‘anomalous transmission’ peaks are broader in the exotic metallic films compared to those formed in 2D aperture array in regular metallic films such as silver, showing that the surface plasmonpolaritons on the filmsurfaces have higher attenuation.
88(2006); http://dx.doi.org/10.1063/1.2175483View Description Hide Description
We report a large enhancement of third-harmonic generation in the one-dimensional dielectric photonic-crystal-based amorphous nanocavity. The enhancement took place at the frequency of defect mode and was a pure nonlinear process. A great increase of third-harmonic intensity up to approximately five orders of magnitude was demonstrated, which was attributed to field localization in the range of nanocavity.
88(2006); http://dx.doi.org/10.1063/1.2175485View Description Hide Description
We report on the use of hyperbranched polymers (HBPs) acting as mobile organic nanoparticles doped in methacrylate photopolymers for highly efficient volume holographic recording. Two types of reduced HBPs having the average size of are synthesized. The diffraction efficiency near 100% in the green and substantive polymerization-shrinkage suppression in this photopolymer system are demonstrated. Periodic assembly of HBPs under holographic exposure is also observed.
88(2006); http://dx.doi.org/10.1063/1.2173262View Description Hide Description
The measurement of minute changes in local gloss has not been presented in international standards due to a lack of suitable glossmeters. The development of a diffractive-element-based glossmeter (DOG) made it possible to detect local variation of gloss from planar and complex-shaped surfaces. Hence, a demand for proper statistical gloss parameters for classifying surface quality by gloss, similar to the standardized surface roughness classification, has become necessary. In this letter, we define statistical gloss parameters and utilize them as an example in the characterization of gloss from metal surface roughness standards by the DOG.
88(2006); http://dx.doi.org/10.1063/1.2173619View Description Hide Description
We have optimized the internal quantum efficiency(IQE) of quantum-well (QW) structures. For an emission wavelength of , a high IQE of 73% was achieved. For a longer emission wavelength, calculations predict higher oscillator strength for thinner QWs but higher In content. We observe an improvement in IQE of almost 50% when reducing the QW width from , and increasing the In content for the whole blue to green spectral region with at . The typical saturation of the output power with increasing current that occurs, particularly for green-light-emitting diodes, is extremely weak in our structures.
88(2006); http://dx.doi.org/10.1063/1.2173707View Description Hide Description
We studied the light illumination effect on the performance of pentacene organic thin-film transistors(TFTs) exhibiting a field-effect mobility of , threshold voltage of and on/off current ratio of . The transfer characteristics of the orgnaic TFT change remarkably by illumination in the subthreshold and off-state regions because of the photogenerated carriers in the TFT channel. The minimum off current increases by under the illumination of . The drain current increases linearly with light intensity in the region where holes are majority carriers. On the other hand, the off-state currents increase superlinearly with light intensity when electrons are majority carriers. The photoleakage current increases with illumination time at the constant temperature. The results can be explained on the basis of the trapping of carriers at the grain boundaries and significant recombination of electrons and holes when electrons are majority carrier. The holes can be trapped at the grain boundaries during illumination, reducing the potential barriers at the boundaries.
88(2006); http://dx.doi.org/10.1063/1.2176852View Description Hide Description
We find experimentally that the relaxation oscillation peak in the relative intensity noise spectrum of a semiconductor laser has a higher damping and lower frequency when we add low frequency noise to the pump current. The broadening of the relaxation oscillation peak with increasing carrier noise level is interpreted as an increase of the nonlinear gain compression with noise strength.
Enhanced efficiency in polymer light-emitting diodes due to the improvement of charge-injection balance88(2006); http://dx.doi.org/10.1063/1.2176856View Description Hide Description
The authors report the enhancement of efficiency of polymer light-emitting diodes(PLEDs) in the study. According to the experimental results, we find that PLEDs,fabricated on irradiated indium-tin-oxide surfaces by excimer laser, with an organic layer between the cathode and the emitting layer may lead to the improvement of charge-injection balance and prevention of cathode metal quenching, resulting in a remarkable increase in external quantum efficiency.
Optical tunneling effect of localized surface plasmon: A simulation study using particle-in-cell method88(2006); http://dx.doi.org/10.1063/1.2176864View Description Hide Description
Optical tunneling through thin metal films with periodic Gaussian-shaped grooves was studied using the particle-in-cell method. For a normally incident TM-polarized wave, the transmission coefficients are maximal in the localized surface plasmon (LSP) modes, which is similar to the predictions of the Drude model, but with lower transmission coefficients. The plasma-plasma interactions partially smear out the LSP modes, which has not been addressed in previous studies that involved the Drude model. Although various heating and cooling processes occur at the air-plasma interface, the temperature of the plasma only slightly affects the transmission coefficients.
88(2006); http://dx.doi.org/10.1063/1.2173718View Description Hide Description
One-dimensional photonic-crystal reflectance filters operating in the near-ultraviolet wavelengths were fabricated using nanoreplica molding from a siliconsurface structure “master” template, patterned using electron-beam lithography. The fabricated devices produce a narrow linewidth reflectance resonance at a wavelength of for TM polarized illumination and a broadband reflectance characteristic between 402 and for TE polarized illumination. The measured reflectance spectra are accurately predicted by Rigorous Coupled Wave Analysis computer simulations, which demonstrate the capability for designing similar filter performance for wavelengths through minor adjustment of the photonic-crystal lattice period.
Observation of large parity-change-induced dispersion in triangular-lattice photonic crystal waveguides using phase sensitive techniques88(2006); http://dx.doi.org/10.1063/1.2174098View Description Hide Description
We experimentally studied W1 triangular-lattice photonic crystal waveguides (PCWs) fabricated on semiconductor-on-insulator substrates using phase-sensitive lock-in techniques. In addition to the improved signal-to-noise ratio for power transmission measurements, we observed two large group delay peaks at frequencies corresponding to the photonic mode gap and parity changes of Bloch modes inside the PCWs.
88(2006); http://dx.doi.org/10.1063/1.2174101View Description Hide Description
We report on a technique for the on-chip sensing of dielectric materials in the terahertz frequency range. We show that an array of band-stop filters, excited by integrated ultrafast photoconductive switches, can be used to sense dielectric loading at a number of distinct lithographically defined locations on a chip simultaneously, each location sensing a different terahertz frequency. This technique is expected to have a range of future applications in the field of on-chip terahertz systems, such as the analysis of deoxyribonucleic acid and other molecular films.
Second-harmonic generation to the green and yellow using picosecond fiber pump sources and periodically poled waveguides88(2006); http://dx.doi.org/10.1063/1.2174102View Description Hide Description
Compact yellow and green picosecond pulse sources are demonstrated that utilize second-harmonic generation in periodically poled potassium titanyl phosphate waveguides. Both systems employ ytterbium-doped fiber pump sources. In the yellow case, efficient single-pass Raman scattering in of dispersion-compensating fiber was additionally used to generate the pump. Raman gain could similarly be used in compact configurations to generate other pump wavelengths for use in frequency upconversion schemes.
88(2006); http://dx.doi.org/10.1063/1.2174104View Description Hide Description
Using terahertz time-domain spectroscopy, we study transmission in one-dimensional arrays of slits fabricated on metal plates by laser machining. The enhanced peaks of zero-order transmission spectra are attributed to the combined effects of Fabry–Perot and surface plasmon resonances. Angle dependence of transmission spectra shows that the strongly surface plasmon-enhanced peaks appear when the Fabry–Perot-type resonance is located nearby in energy. This means that surface waves traveling in the horizontal direction couple with nearest Fabry–Perot resonance to generate enhanced peaks. These results are in excellent agreement with theoretical calculations.
88(2006); http://dx.doi.org/10.1063/1.2174106View Description Hide Description
The design, fabrication, and characterization of an amplifying transverse magnetic (TM)-mode optical waveguide isolator operating at a wavelength of are presented. The magneto-optical Kerr effect induces nonreciprocal modal absorption in a semiconductor optical amplifier with a laterally magnetizedferromagneticmetal contact. Current injection in the active structure compensates for the loss in the forward propagation direction. Monolithic integration of this optical isolator configuration with active InP-based photonic devices is straightforward. The combination of active material and the metal alloy results in greatly improved performance. TM mode isolation and significantly reduced insertion loss are demonstrated.
88(2006); http://dx.doi.org/10.1063/1.2172412View Description Hide Description
Concave pyramids are created in the (100) surface of a silicon wafer by anisotropicetching in potassium hydroxide. High quality micromirrors are then formed by sputteringgold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into micro-optoelectromechanical systems and atom chips. We have shown that structures of this shape can be used to laser-cool and hold atoms in a magneto-optical trap.
88(2006); http://dx.doi.org/10.1063/1.2170427View Description Hide Description
For the purpose of exploring near-infrared emission, the photoluminescence (PL) and electro- luminescence (EL) of N, -bis(neopentyl)-3,4:9,10-perylenebis(dicarboximide) (BNPTCD): tris(8-quinolinolato)aluminum mixed films were investigated. It was found that BNPTCD: mixed films exhibit PL in the near-infrared wavelength region and that organic light-emitting diodes using highly doped with BNPTCD as an emitting layer exhibit near-infrared EL with a peak at 805 nm originating from BNPTCD aggregates.
88(2006); http://dx.doi.org/10.1063/1.2174832View Description Hide Description
We have realized a terahertz (THz)-wave source employing difference frequency generation (DFG) from a quasi-phase-matched GaP stack pumped at . We observed THz waves with enhanced power by quasi-phase matching (QPM) in the ⟨110⟩ direction of GaP with a ⟨111⟩ polarization direction for the incidence of two pump lights with the same propagation and polarization directions. We obtained THz-wave power proportional to the product of two pump-light powers due to DFG. We also confirmed that power peaks appeared at around 1 and reflecting the first- and the third-order QPM, respectively.
88(2006); http://dx.doi.org/10.1063/1.2174087View Description Hide Description
The aberrations of a spherical lens composed of left-handed materials are studied in this letter. Five Seidel aberrations (spherical, coma, astigmatism, field curvature, and distortion) as a function of the refractive index and shape factor of the lens are considered. Our numerical calculations show that the negative refractive index gives much larger windows of small values of aberrations than the positive index, which will significantly enhance the flexibility for the design of an optical lens. Two possible regions with optimized aberrations are proposed: , and and .
88(2006); http://dx.doi.org/10.1063/1.2177353View Description Hide Description
A tunable wavelength filter was proposed and demonstrated by using the ultraviolet nanoimprint technique. It consists of a Bragg grating in polymer waveguides and a heating electrode. The creation of the grating was substantially simplified with the introduction of a smart imprint stamp containing a waveguide pattern integrated with the grating pattern. The center wavelength of the filter was successfully tuned by taking advantage of the thermooptic effect in polymers, which was induced by supplying electrical power to the electrode. For the fabricated device, a transmission dip of and a bandwidth of were obtained at the Bragg wavelength of . The achieved thermooptic tuning rate was , while the center wavelength was shifted from to with the electrical power consumption of .