Volume 101, Issue 2, 09 July 2012
- photonics and optoelectronics
- surfaces and interfaces
- structural, mechanical, optical, and thermodynamic properties of advanced materials
- magnetics and spintronics
- superconductivity and superconducting electronics
- dielectrics, ferroelectrics, and multiferroics
- nanoscale science and technology
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
- energy conversion and storage
- interdisciplinary and general physics
Index of content:
In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.
- PHOTONICS AND OPTOELECTRONICS
101(2012); http://dx.doi.org/10.1063/1.4733972View Description Hide Description
We present an ultrafast all-optical gated amplifier, or transistor, consisting of a forest of ZnOnanowire lasers. A gate light pulse creates a dense electron-hole plasma and excites laser action inside the nanowires. Source light traversing the nanolaser forest is amplified, partly as it is guided through the nanowires, and partly as it propagates diffusively through the forest. We have measured transmission increases at the drain up to a factor 34 for 385-nm light. Time-resolved amplification measurements show that the lasing is rapidly self-quenching, yielding pulse responses as short as 1.2 ps.
Frequency tunable x-ray/γ-ray source via Thomson backscattering on flying mirror from laser foil interaction101(2012); http://dx.doi.org/10.1063/1.4734503View Description Hide Description
A scheme to generate a frequency tunable x-ray/γ-ray source via Thomson backscattering is proposed. In this model, a few-cycle drive pulse with relativistic intensity interacts with a target (combined with a thin and a thick foil) to produce a flying mirror, and a counter propagating probe pulse is applied to generate a high frequency pulse on it. By adjusting the separation between these two foils, the frequency of the Thomson backscattering light generated from the flying mirror can be tuned in a range from to , i.e., x-ray or γ-ray with tunable frequency is obtained. The energy dispersion of the flying mirror, as well as the spectrum width of the Thomson backscattering are studied.
101(2012); http://dx.doi.org/10.1063/1.4734389View Description Hide Description
Using a transport model based on the density matrix formalism, a fully automatized technique to design quantum cascade structures in the mid-infrared is presented that implements a genetic algorithm where the wallplug efficiency has been used as merit factor. Starting from a reference design, the model converges after few generations on an optimized design that presents a better carrier injection in the upper lasing state. Both the designs have been fabricated using buried heterostructure process and the optimized design shows a pronounced increase in the laser operation range and higher output powers. In good agreement with the simulations, the laser efficiency increases from 5% to 12%.
Negative refraction and partial focusing with a crossed wire mesh: Physical insights and experimental verification101(2012); http://dx.doi.org/10.1063/1.4734510View Description Hide Description
We experimentally verify that a flat metamaterial lens formed by nonconnected crossed metallic wires enables the partial focusing of electromagnetic waves, as a consequence of the phenomenon of all-angle broadband negative refraction in such media. We prove that the strength of the negative refraction effect can be controlled by adjusting the angle between the crossed wires.
101(2012); http://dx.doi.org/10.1063/1.4734640View Description Hide Description
We report an efficient and low-loss polarization rotator based on mode evolution using horizontal slot waveguide. The device is fabricated using complementary metal–oxide–semiconductor compatible processes, which allows monolithic integration with active drive electronics and other photonic components. A rotator fabricated with 100 μm transition length provides a high extinction ratio >14 dB for both transverse-magnetic (TM)-transverse-electric (TE) and TE-TM rotation. The excess loss of the device is <1 dB for both rotations as etching of the bottom Si waveguide is prevented. The device also exhibits a uniform rotation response over C+L band wavelength range of 1530-1600 nm.
High operating temperature interband cascade midwave infrared detector based on type-II InAs/GaSb strained layer superlattice101(2012); http://dx.doi.org/10.1063/1.4733660View Description Hide Description
We report on an interband cascade mid-wave infrared (MWIR) detector based on type-II InAs/GaSb/AlSb strained layer superlattices (T2SL). The reported device has a seven-stage cascade region, each segment containing a MWIR absorber region, a graded T2SL transport region, and an interband tunneling region. Above room temperature spectral response was observed, with a cutoff wavelength of 7 μm at 420 K. Detailed radiometric measurements yielded a Johnson noise limited detectivity of 3.0 × 1011 cmHz1/2W−1 (8.9 × 108 cmHz1/2W−1) and a dark current density of 3.6 × 10−7 A/cm−2 (7.3 × 10−3 A/cm−2) near zero bias with a 100% cutoff wavelength of 5.2 μm and 6.2 μm at 77 K (295 K), respectively, with an estimated 36.2% QE.
101(2012); http://dx.doi.org/10.1063/1.4734511View Description Hide Description
We demonstrate intracavity terahertz generation from an output coupler of a compact dual-frequency solid state laser. The output coupler consisting of unbonded and stacked GaP plates is used as a second-order nonlinear medium where the difference-frequency generation takes place. When quasi-phase matching is achieved within the alternatively rotated GaP plates, terahertz output power is significantly enhanced compared with that for the corresponding external-cavity configuration.
A magnifying fiber element with an array of sub-wavelength Ge/ZnSe pixel waveguides for infrared imaging101(2012); http://dx.doi.org/10.1063/1.4734787View Description Hide Description
We demonstrate an array of tapered Ge-core/ZnSe-cladding waveguides in a silica fiber matrix for infrared image transfer and a pixel magnification of 3.5× at 3.39 μm and 10.64 μm wavelengths. The structure was synthesized by a high-pressure chemical vapor deposition technique to deposit the semiconductorwaveguides within the holes of a silica based microstructured optical fiber. The core/cladding structure reduces the optical propagation loss through the waveguides, and good isolation between the pixels is demonstrated. With further material improvements, these structures could be useful for applications such as infrared endoscopic imaging.
101(2012); http://dx.doi.org/10.1063/1.4732793View Description Hide Description
We demonstrate near field enhancement generation in silver nanoantenna-superlens systems via numerical modeling. Using near-field interference and global optimization algorithms, we can design nanoantenna-superlens systems with mismatched permittivities, whose performance can match those with matched permittivities. The systems studied here may find broad applications in the fields of sensing, such as field-enhanced fluorescence and surface-enhanced Raman scattering, and the methodology used here can be applied to the designing and optimization of other devices, such as two-dimensional near field focusing lens.
101(2012); http://dx.doi.org/10.1063/1.4735258View Description Hide Description
In this paper, the Fano resonance in the “eye-like” microring resonator system (EMRS) is theoretically and experimentally investigated. The asymmetric Fano-resonance line shape of EMRS is generated by adding a microring inside and coupling with the outer ring to produce a nonlinear phase shift. The EMRS was fabricated on silicon-on-insulator wafer by the complementary metal-oxide-semiconductor compatible process. Compared to the conventional single-stage microring add-drop filter structure, the maximum sharpness of the transmission of the drop port is enhanced 3 times, and the drop port extinction ratio is increased by about 20 dB. The experimental results are in good agreement with the theoretical analysis.
101(2012); http://dx.doi.org/10.1063/1.4735319View Description Hide Description
We revisit stimulated-emission-depletion (STED) nanoscopy theory for the case when metal nanoparticles are used to improve the nanoscope’s performance. We show that the improved performance can be estimated in a simple way with no need for heavy computations. We then systematically study the dependence of the improved performance on the field and decay rate enhancements, as well as on the STED pulse and time-gating durations.
First-order light-induced orientation transition in nematic liquid crystal in the presence of low-frequency electric field101(2012); http://dx.doi.org/10.1063/1.4736409View Description Hide Description
Director deformation in a planar nematic liquid crystal(NLC) with negative optical nonlinearity (director rotates away from the light field) has been studied. First-order orientation transition and a wide hysteresis loop were observed at changing the light intensity in the presence of an ac field that is non-perpendicular to the undistorted director of liquid crystal due to pretilt. The theory of light beam interaction with NLC under ac field was constructed.
Electrical measurement of internal quantum efficiency and extraction efficiency of III-N light-emitting diodes101(2012); http://dx.doi.org/10.1063/1.4736565View Description Hide Description
We propose a direct electrical measurement method for determining the extraction efficiency (EXE) and internal quantum efficiency(IQE) of III-Nitride light-emitting diodes(LEDs). The method is based on measuring the optical output power as a function of injection current at current densities near the external quantum efficiency (EQE) maximum and extracting IQE and EXE from the measurement data. In contrast to conventional methods, our method requires no low temperaturemeasurements or prior knowledge of the device structure. The method is far more convenient than commonly used methods because it enables measuring the EXE and IQE of different LED structures at room temperature directly in a repeatable and consistent way. This enables convenient comparison of LED structures. We apply the method to determine the IQE and EXE of one commercial LED and selected self-grown planar LED chips to compare the effects of different LED structure designs. Our results are in line with published experimental results and also give more insight to our earlier findings regarding the effects of growth parameters on the quantum efficiency. In addition, our measurement method allows estimating the Shockley-Read-Hall and radiative recombination parameters if the Auger parameter is known.
101(2012); http://dx.doi.org/10.1063/1.4727901View Description Hide Description
Small-core photonic-crystal fibers (PCFs) are shown to enhance the locality of optical interrogation in fiber-probe-based imaging. We demonstrate that, in a typical fluorescence imaging experiment, the longitudinal dimension of the interrogated region closely follows the scaling with the effective mode radius a m and the beam-divergence angle θ d. The confinement of optical interrogation provided by small-core, high-index-step PCF probes is high enough to enable interrogation of individual neurons in a typical brain imaging experiment.
Nanostructure Ag dots for improving thermal stability of Ag reflector for GaN-based light-emitting diodes101(2012); http://dx.doi.org/10.1063/1.4737015View Description Hide Description
We report the improved thermal stability of Ag reflectors for GaN-based light-emitting diodes (LEDs) using Ag nano-dots (∼65–∼190 nm in size). The nano-dot Ag samples show much higher reflectance than the Ag only samples. The annealed nano-dot Ag samples exhibit a smoother surface, where the grains contain numerous micro-twins. 〈111〉 texture becomes more dominantly evolved in the nano-dot Ag samples than in the Ag only samples after annealing. LEDs with the 300 °C-annealed nano-dot Ag reflectors exhibit 15%–36% higher output power (at 20 mA) than LEDs with the 300 and 400 °C-annealed Ag only reflectors.
Directional whispering gallery mode emission from Limaçon-shaped electrically pumped quantum dot micropillar lasers101(2012); http://dx.doi.org/10.1063/1.4733726View Description Hide Description
We experimentally demonstrate directional far field emission from whispering gallery modes(WGMs) in electrically driven quantum dot micropillar lasers. In-plane directionality of whispering gallery mode emission is obtained by patterning micropillars with Limaçon-shaped cross-section and an upper air-bridge contact for current injection. The micropillar lasers with radii R0 down to 4.5 μm show Q-factors of 40 000 and threshold currents of 40 μA at low temperature. We achieved a far field divergence of about 30° and a directionality of 1.67 ± 0.15 for an optimal Limaçon deformation factor ɛ ≈ 0.5. Parameter dependent studies of the directional emission as a function of ɛ reveal good qualitative agreement with theoretical predictions.
- SURFACES AND INTERFACES
101(2012); http://dx.doi.org/10.1063/1.4733336View Description Hide Description
We report on the attainment of high quality surface passivation of crystalline silicon using facile native oxide and plasma enhanced chemical vapour deposition SiNx. Using systematic measurements of excess carrier density dependent minority carrier lifetime, it is observed that the inferred interface defect density decreases with increasing native oxide thickness while the interfacecharge density remains unchanged with thickness, which ranges from 0.2 Å to 10 Å. A surface recombination velocity of 8 cm/s is attained corresponding to a native oxide layer thickness of ∼10 Å. Similar chemically grown oxide layer followed by SiNxdeposition is shown to yield comparable passivation, indicating practical viability of the passivation scheme.
Thickness effects on the magnetic and electrical transport properties of highly epitaxial LaBaCo2O5.5+δ thin films on MgO substrates101(2012); http://dx.doi.org/10.1063/1.4734386View Description Hide Description
The transport properties of double perovskite LaBaCo2O5.5+δ thin films with different thicknesses were systemically studied. A thin (7 nm in thickness), disordered LaBaCo2O5.5+δ layer was formed at the interface between the film and substrate. The films had a typical semiconductor behavior with antiferromagnetic and ferromagnetic behavior coexisting at low temperature. Although the Curie temperature was independent of the film thickness, the coercive fields and magnetizations increase with increasing the film thickness. An ultra large magnetoresistance effect value of about 44% was obtained at 60 K for the film of 82 nm.
101(2012); http://dx.doi.org/10.1063/1.4734396View Description Hide Description
The current process of growinggraphene by thermal decomposition of 3C-SiC(100) on silicon is technologically attractive. Here, we study epitaxialgraphene on single domain 3C-SiC films on off-axis Si(100). The structural and electronic properties of such graphene layers are explored by atomic force microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. Using low energy electron diffraction, we show that graphene exhibits single planar domains. Near-edge x-ray absorption fine structure is used to characterize the sample, which confirms that the graphene layers present sp 2 hybridization and are homogeneously parallel to the substrate surface.
101(2012); http://dx.doi.org/10.1063/1.4736572View Description Hide Description
NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast carrier dynamics of the sample were studied by time-resolved transient differential reflection (R/R). The data show two exponential relaxation processes. The slow relaxation process (2ps) is ascribed to low energy acoustic phonon mediated scattering. The electron-phonon coupling and first-principles calculation results demonstrate that -OH and -ONa groups in the sample are strongly coupled. Thus, we attribute the fast relaxation process (0.17ps) to the coupling of hydroxyl and -ONa groups in the sample.