Volume 99, Issue 16, 17 October 2011
- 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
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
Index of content:
Confining blended poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester organic solar cellactive layers within nanometer-scale cylindrical pores nearly double the supported short-circuit photocurrent density compared to equivalent unconfined volumes of the same blend and increases the poly(3-hexylthiophene) hole mobility in the blend by nearly 500 times. Grazing incidence x-ray diffraction measurements show that the confinement changes the polymer orientation distribution, suppressing low charge conductivity orientations while simultaneously disrupting polymer ordering.
- LASERS, OPTICS, AND OPTOELECTRONICS
99(2011); http://dx.doi.org/10.1063/1.3651490View Description Hide Description
We report a magnetic field sensor having advantages of both photonic crystal fiber and optofluidics, combining them on a single platform by infiltrating small amount of Fe3O4 magnetic optofluid/nanofluid in cladding holes of polarization-maintaining photonic crystal fiber. We demonstrated that magnetic field of few mT can be easily and very well detected with higher sensitivity of 242 pm/mT. The change in the birefringence values has been correlated to the response of nanofluid to applied field.
99(2011); http://dx.doi.org/10.1063/1.3651491View Description Hide Description
Systems of photonic crystalcavities coupled to quantum dots are a promising architecture for quantum networking and quantum simulators. The ability to independently tune the frequencies of laterally separated quantum dots is a crucial component of such a scheme. Here, we demonstrate the independent tuning of laterally separated quantum dots in photonic crystalcavities coupled by in-plane waveguides by implanting lines of protons which serve to electrically isolate different sections of a diode structure.
99(2011); http://dx.doi.org/10.1063/1.3652760View Description Hide Description
The Raman effect is typically observed by irradiating a sample with an intense light source and detecting the minute amount of frequency shifted scattered light. We demonstrate that Raman molecular vibrational resonances can be detected directly through an entirely different mechanism—namely, a force measurement. We create a force interaction through optical parametric down conversion between stimulated, Raman excited, molecules on a surface and a cantilevered nanometer scale probe tip brought very close to it. Spectroscopy and microscopy on clusters of molecules have been performed. Single molecules within such clusters are clearly resolved in the Raman micrographs. The technique can be readily extended to perform pump probe experiments for measuring inter- and intramolecular couplings and conformational changes at the single molecule level.
99(2011); http://dx.doi.org/10.1063/1.3650268View Description Hide Description
We demonstrate polariton lasing in a bulk ZnO planar microcavity under non-resonant optical pumping at a small negative detuning (δ ∼ −1/6 the 130 meV vacuum Rabi splitting) and a temperature of 120 K. The strong coupling regime is maintained at lasing threshold since the coherent nonlinear emission from the lower polariton branch occurs at zero in-plane wavevector well below the uncoupled cavity mode. The contribution of multiple localized polariton modes above threshold and the non-thermal polariton statistics show that the system is in a far-from-equilibrium regime, likely related to the moderate photon lifetime and in-plane photonic disorder in the cavity.
99(2011); http://dx.doi.org/10.1063/1.3652908View Description Hide Description
The origin of the decoherence in superconductingnanowire single-photon detectors, the so-called dark count, was investigated. We measured the direct-current characteristics and bias-current dependencies of the dark count rate in a wide range of temperatures from 0.5 K to 4.0 K, and analyzed the results by theoretical models of thermal fluctuations of vortices. Our results indicate that the current-assisted unbinding of vortex-antivortex pairs is the dominant origin of the dark count.
99(2011); http://dx.doi.org/10.1063/1.3653277View Description Hide Description
We studied the dependence of high harmonic generation efficiency on the ellipticity of 400 nm driving laser pulses at 7.7 × 1014 W/cm2 and compared it with the 800 nm driving laser under the same conditions. The measured decrease of high harmonic yield with the ellipticity of the 400 nm laser is ∼1.5 times slower that of the 800 nm, which agrees well with theoretical predictions based on a semi-classical model. The results indicate that it is feasible to use the generalized double optical gating with 400 nm lasers for extracting single attosecond pulses with high efficiency.
99(2011); http://dx.doi.org/10.1063/1.3653470View Description Hide Description
We report the preparation and characterization of an attenuated total reflection(ATR) GeO2 hollow waveguide. An internally GeO2-coated silicaglass tube (bore size 1.0–1.2 mm, length 1.2 m) was prepared using a homogeneous liquid phase deposition method. Kramers-Kronig analysis reveals that the GeO2 cladding material qualifies as a reflective layer (nr < 1) for the ATR hollow waveguide structure. ATR-transmission of 9.6–11.7 μm light through HE11 mode is confirmed by loss spectrum analysis of the sample. The straight and bending (30°) transmission losses for delivery of a ∼40 W CO2laser beam (10.6 μm) are 0.56 dB/m and 1.64 dB/m, respectively.
99(2011); http://dx.doi.org/10.1063/1.3654149View Description Hide Description
We propose a design for a plasmoniccoppermetamaterial with a negative index of refraction at visible/near-infrared wavelengths. Using numerical simulations, we demonstrate negative refraction by a coppermetamaterialprism and perform a parameter extraction technique to verify the sign of the effective, electric permittivity and magnetic permeability. Our proposed design has a figure of merit comparable to similar silver-based metamaterials operating in the visible/near-infrared range. These findings have implications for the design of low cost plasmonic devices and negative-index metamaterials in the visible/near-infrared.
99(2011); http://dx.doi.org/10.1063/1.3654155View Description Hide Description
A super-thin AlN layer is inserted between the intrinsic InGaN and p-InGaN in the InGaNsolar cell structure to improve the photovoltaicproperty. The dark current is markedly decreased by more than two orders of magnitude and the short-circuit current density is increased from 0.77 mA/cm2 to 1.25 mA/cm2, leading to a doubled conversion efficiency compared to the conventional structure. Electrical transport analysis reveals that the forward electrical property is greatly improved in the range of open circuit voltage and the leakage current mechanism changes from defect related Poole-Frenkel emission to interface tunneling emission. The improvement on the electrical and photovoltaicproperties is ascribed to insertion of the AlN interlayer, which not only provides a barrier to reduce tunneling for electrons, but also suppresses the nonradiative recombination.
99(2011); http://dx.doi.org/10.1063/1.3655155View Description Hide Description
We present a study on the light extraction properties of thin filmlight-emitting diodes(LEDs) based on the radiative transfer theory. We show that the well known ergodic limit for absorptivity in texturedsolar cells also applies to emissivity in LEDs accordance with the Kirchhoff’s radiation law. This limit for the emission enhancement by surfacetexturing in LEDs is fundamental and cannot be exceeded even with index-matched optics. We further carry out numerical calculations accounting for realistic absorption in typical GaN-InGaN LEDs to compare their performance with the ergodic limit for non-absorbing structures. The results show that the optical power of InGaN-GaN LED designs can be improved by a substantial factor of 2–4 with texturedsurfaces and engineering of the emission pattern and provide a guideline for more efficient LED designs.
99(2011); http://dx.doi.org/10.1063/1.3655328View Description Hide Description
A flexural wave is applied to an optical fiber during the process of Bragg grating inscription using the direct writing method through a phase mask. Using this approach, we can dither the writing process to allow complex grating writing. Examples we demonstrate are tunable sampled gratings and phase-shifted gratings.
Simulation of a Smith-Purcell free-electron laser with sidewalls: Copious emission at the fundamental frequency99(2011); http://dx.doi.org/10.1063/1.3641471View Description Hide Description
The two-dimensional theory of the Smith-Purcell free-electron laser of Andrews and Brau [H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004)] predicts that coherent Smith-Purcell radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. A particle-in-cell simulation shows that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation can be copiously emitted at the fundamental frequency, for a well-defined range of beam energy.
99(2011); http://dx.doi.org/10.1063/1.3653242View Description Hide Description
We designed and fabricated planar terahertz (THz) metamaterials made from superconducting NbN films to mimic electromagnetically induced transparency (EIT) system. They are characterized using THz time domain spectroscopy over a temperature range from 8 to 300 K. High transmittance and large delay-bandwidth product at transparency window are demonstrated, which mainly arise from the enhanced coupling and decreased damping in superconducting state. The EIT-like spectral response could be tuned in a wide frequency range. By applying two dark resonators with different resonance frequencies coupled with a radiative resonator, we experimentally demonstrated the planar metamaterials mimicking four-level EIT system.
99(2011); http://dx.doi.org/10.1063/1.3654156View Description Hide Description
Optical switching of the spectrum and polarization of terahertz radiation from split-ring resonator-loaded photoconductive antennas has been demonstrated. The switching is based on the sensitivity of the resonance of a split-ring resonator on a photoconductive substrate to a change in the capacitance induced by optical pulse irradiation. The spectral and polarizationcharacteristics of the split-ring resonator-loaded photoconductive antennas are discussed in terms of the coupling between the electric dipole induced by the pump laser and the eigenmodes of the split-ring resonators.
99(2011); http://dx.doi.org/10.1063/1.3655330View Description Hide Description
An Er/Yb silicate strip loaded waveguide was fabricated for optical amplification purpose. A 2.4-μm-wide SiO2 strip was deposited on top of the Er/Yb silicate active layer. Experiment data showed a 5.5 dB signal enhancement in a 7.8-mm-long waveguide pumped by a laser of 372 mW at 1480 nm. The signal is not saturated and can be further enhanced by increasing pumping power and decreasing waveguide loss. The strong red light emission at 660 nm was also observed due to excited stateabsorption and Yb3+ participated energy transfer upconversion processes.
99(2011); http://dx.doi.org/10.1063/1.3655331View Description Hide Description
We present high-power single-cycle carrier-envelope phase locked THz pulses at a central frequency of 2.1 THz with MV/cm electric field strengths and magnetic field strengths beyond 0.3 T. The THz radiation is generated by optical rectification in an organic salt crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate called DAST pumped with the signal wavelength of a powerful optical parametric amplifier. Conversion efficiencies of more than 2% are reported.
Polarization-based all-optical logic controlled-NOT, XOR, and XNOR gates employing electro-optic effect in periodically poled lithium niobate99(2011); http://dx.doi.org/10.1063/1.3656000View Description Hide Description
Based on electro-optic Pockels effect of periodically poled lithium niobate, different polarization-based binary all-optical logic functions: controlled-NOT, XOR, and XNOR gates were demonstrated by altering the linear polarization state of input optical signal about 90° on the polarization plant. Because the depletion of signal intensity in polarization-based logic gates is smaller than that of digital logic signal in intensity-based logic gates and almost negligible, this scheme has potential application in realizing complex logic functions by cascading several basic gates.
Strain-induced tuning of the emission wavelength of high quality GaAs/AlGaAs quantum dots in the spectral range of the 87Rb D2 lines99(2011); http://dx.doi.org/10.1063/1.3653804View Description Hide Description
Reversible biaxial strains are used for tuning the emission wavelengths of high quality GaAs/AlGaAs quantum dots(QDs) in the spectral range of the 87Rb D2 lines. The strain is transferred by integrating free standing (Al)GaAs nanomembranes, containing QDs, onto piezoelectric actuators. Narrow excitonic emission lines as sharp as 25 μeV are shown, and a tuning range larger than 5 nm is demonstrated. This range corresponds to an induced anisotropic biaxial strain of the order of 0.15%, as evaluated from the shift in the emission of the GaAs from the nanomembranes. The presented on-chip technology is potentially interesting for future quantum memories based on hybrid semiconductor-atomic interfaces.
99(2011); http://dx.doi.org/10.1063/1.3656073View Description Hide Description
Large cross-section GaNwaveguides are proposed as a suitable architecture to achieve integrated quantum photonic circuits. Directional couplers with this geometry have been designed with aid of the beam propagation method and fabricated using inductively coupled plasmaetching.Scanning electron microscopy inspection shows high quality facets for end coupling and a well defined gap between rib pairs in the coupling region. Optical characterization at 800 nm shows single-mode operation and coupling-length-dependent splitting ratios. Two photon interference of degenerate photon pairs has been observed in the directional coupler by measurement of the Hong-Ou-Mandel dip [C. K. Hong, et al., Phys. Rev. Lett. 59, 2044 (1987)] with 96% visibility.
- PLASMAS AND ELECTRICAL DISCHARGES
99(2011); http://dx.doi.org/10.1063/1.3652705View Description Hide Description
Efficient proton acceleration by the interaction of an intense femtosecond laser pulse with a solid foil has been demonstrated. An aluminumcoating (thickness: 0.2 μm) on a polyethylene (PE) foil was irradiated at 2 × 1018 W/cm2 intensity. The protons from the aluminum-disk (diameter: 150 μm to 15 mm) foil were accelerated to much higher energy in comparison with conventional targets such as PE and aluminum-coated PE foils. The fast electron signal along the foil surface was significantly higher from the aluminum-coated PE foil. The laser-proton acceleration appeared to be affected to the size of surrounding conductive material.