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12 Mar 2012

Volume 100, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages)

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz
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Holographic optical bottle beams

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz

Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages) | Cited 7 times

Online Publication Date: 12 March 2012

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We present a convolution approach for the generation of optical bottle beams that combines established techniques of holographic optical trapping with hollow intensity distributions in order to manipulate absorbing particles. The versatility of our method is demonstrated by the simultaneous stable trapping of multiple particles at defined positions. Furthermore, the presented phase shaping technique allows for the dynamic manipulation of absorbing particles along arbitrary paths.
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42.40.-i Holography
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Anti resonant reflecting optical waveguide structure based on oxidized porous silicon for label free bio sensing applications

L. Haji, M. Hiraoui, N. Lorrain, and M. Guendouz

Appl. Phys. Lett. 100, 111102 (2012); http://dx.doi.org/10.1063/1.3692588 (4 pages) | Cited 2 times

Online Publication Date: 12 March 2012

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In this letter we report on the use of an electrochemical process for the fabrication of anti resonant reflecting optical waveguide based on oxidized porous silicon. This method is known to allow the formation of various photonic structures (Bragg mirror, microcavity), thanks to the easy and in situ modulation of the porosity and thus of the refractive index. Planar anti resonant reflecting optical waveguide structure made from porous silicon is demonstrated to be very effective for low losses as compared to conventional resonant waveguide. Optical measurements carried out for TE and TM polarizations are reported and related to optical sensing.
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87.85.J- Biomaterials
82.45.-h Electrochemistry and electrophoresis
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
81.05.Rm Porous materials; granular materials

Quantum rod emission coupled to plasmonic lattice resonances: A collective directional source of polarized light

S. R. K. Rodriguez, G. Lozano, M. A. Verschuuren, R. Gomes, K. Lambert, B. De Geyter, A. Hassinen, D. Van Thourhout, Z. Hens, and J. Gómez Rivas

Appl. Phys. Lett. 100, 111103 (2012); http://dx.doi.org/10.1063/1.3693397 (3 pages) | Cited 7 times

Online Publication Date: 12 March 2012

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We demonstrate that an array of optical antennas may render a thin layer of randomly oriented semiconductor nanocrystals into an enhanced and highly directional source of polarized light. The array sustains collective plasmonic lattice resonances, which are in spectral overlap with the emission of the nanocrystals over narrow angular regions. Consequently, different photon energies of visible light are enhanced and beamed into definite directions.
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42.79.-e Optical elements, devices, and systems

Strong terahertz absorption using SiO2/Al based metamaterial structures

Fabio Alves, Brian Kearney, Dragoslav Grbovic, Nickolay V. Lavrik, and Gamani Karunasiri

Appl. Phys. Lett. 100, 111104 (2012); http://dx.doi.org/10.1063/1.3693407 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2012

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Metamaterial absorbers with nearly 100% absorption in the terahertz (THz) spectral band have been designed and fabricated using a periodic array of aluminum (Al) squares and an Al ground plane separated by a thin silicon dioxide (SiO2) dielectric film. The entire structure is less than 1.6 mm thick making it suitable for the fabrication of microbolometers or bi-material sensors for THz imaging. Films with different dielectric layer thicknesses exhibited resonant absorption at 4.1, 4.2, and 4.5 THz with strengths of 98%, 95%, and 88%, respectively. The measured absorption spectra are in good agreement with simulations using finite element modeling.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Switchable liquid crystal grating with sub millisecond response

F. Fan, A. K. Srivastava, V. G. Chigrinov, and H. S. Kwok

Appl. Phys. Lett. 100, 111105 (2012); http://dx.doi.org/10.1063/1.3693601 (4 pages) | Cited 7 times

Online Publication Date: 12 March 2012

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In present article, we disclose a fast switchable grating based on nematic liquid crystals. A fine striped electrode has been exploited to generate the grating profile and a driving scheme to drive the grating cell has also been proposed, which enable us to drive the cell up to very high frequency (∼2 kHz) with evident saturated optical states. The response time for the first order diffracted beam, at the electric field of 10 V/μm, is less than 100 μs and optical contrast is higher than 400:1. Thus, the proposed LC grating could find application in several advance electro-optical devices.
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42.79.Dj Gratings
42.70.Df Liquid crystals

Efficiency droop in AlGaInP and GaInN light-emitting diodes

Jong-In Shim, Dong-Pyo Han, Hyunsung Kim, Dong-Soo Shin, Guan-Bo Lin, David S. Meyaard, Qifeng Shan, Jaehee Cho, E. Fred Schubert, Hyunwook Shim, and Cheolsoo Sone

Appl. Phys. Lett. 100, 111106 (2012); http://dx.doi.org/10.1063/1.3694044 (4 pages) | Cited 3 times

Online Publication Date: 13 March 2012

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At room temperature, AlGaInP pn-junction light-emitting diodes (LEDs) emitting at 630 nm do not exhibit an efficiency droop. However, upon cooling the AlGaInP LEDs to cryogenic temperatures, they show a pronounced efficiency droop. We attribute the efficiency droop in AlGaInP LEDs to electron-drift-induced reduction in injection efficiency (i.e., carrier leakage out of the active region) mediated by the asymmetry of the pn junction, specifically the disparity between electron and hole concentrations and mobilities, with the concentration disparity exacerbated at low temperatures.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Time-resolved single-shot imaging of femtosecond laser induced filaments using supercontinuum and optical polarigraphy

Lihe Yan (闫理贺), Xiaofang Wang (王小芳), Jinhai Si (司金海), Shigeki Matsuo (松尾繁樹), Tao Chen (陈涛), Wenjiang Tan (谭文疆), Feng Chen (陈烽), and Xun Hou (侯洵)

Appl. Phys. Lett. 100, 111107 (2012); http://dx.doi.org/10.1063/1.3694051 (3 pages) | Cited 1 time

Online Publication Date: 13 March 2012

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We have developed an ultrafast time-resolved imaging technique for the propagation dynamics of ultrashort laser pulses in transparent media. This method utilizes the optical polarigraphy technique and a chirped supercontinuum as the probe light. The supercontinuum senses the instantaneous birefringence induced by the propagation of an intense pulse, and a polarigraphy image with different color distributions could be obtained. Using this method, we performed a space-time characterization of the filament induced by a femtosecond laser pulse in CS2, indicating that this technique could be used for the single-shot imaging of pulse propagation dynamics.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Refractive index sensor based on hybrid coupler with short-range surface plasmon polariton and dielectric waveguide

Boyu Fan, Fang Liu, Yunxiang Li, Yidong Huang, Yoshikatsu Miura, and Dai Ohnishi

Appl. Phys. Lett. 100, 111108 (2012); http://dx.doi.org/10.1063/1.3693408 (3 pages) | Cited 4 times

Online Publication Date: 13 March 2012

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An integrated sensor based on a vertical hybrid coupler composed of a short-range surface plasmon polariton (SRSPP) waveguide and a SiNx dielectric waveguide has been realized. The output power of the sensor is observed to change drastically with the refractive index of the detection liquid, and the sensing region can be adjusted by varying the width of the SiNx waveguide. The resolution is estimated to be as high as 7.3 × 10−6 refractive index units. This sensor is expected to have significantly high effective sensitivity for detecting a hundred-nanometer-thick layer owing to the highly bounded field of the SRSPP mode.
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07.60.Hv Refractometers and reflectometers
42.79.Gn Optical waveguides and couplers
73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Terahertz electroluminescence from 6Н-SiC structures with natural superlattice

V. I. Sankin, A. V. Andrianov, A. O. Zakhar`in, and A. G. Petrov

Appl. Phys. Lett. 100, 111109 (2012); http://dx.doi.org/10.1063/1.3693418 (4 pages) | Cited 1 time

Online Publication Date: 13 March 2012

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We report on efficient terahertz emission in the region of 1.5-2 THz from high electric field biased 6H-SiC structures with a natural superlattice (NSL) at liquid helium temperatures. The shape of the THz emission spectrum, the linear dependence of its maximum on the bias, the characteristic field strength required to achieve the emission, and the linear polarization of the emission along the natural superlattice axis allow it to be attributed to steady-state Bloch oscillations of electrons in the 6H-SiC natural superlattice.
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78.70.Gq Microwave and radio-frequency interactions
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.60.Fi Electroluminescence

Integrated photonic structures for light trapping in thin-film Si solar cells

Xing Sheng, Steven G. Johnson, Lirong Z. Broderick, Jurgen Michel, and Lionel C. Kimerling

Appl. Phys. Lett. 100, 111110 (2012); http://dx.doi.org/10.1063/1.3693613 (3 pages)

Online Publication Date: 13 March 2012

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We explore the mechanisms for an efficient light trapping structure for thin-film silicon solar cells. The design combines a distributed Bragg reflector (DBR) and periodic gratings. Using photonic band theories and numerical simulations, we discover that light can be scattered into the DBR by gratings, with an unusual way of light trapping different from metal reflectors and photonic crystals. We further investigate the influence of DBR on generated photocurrent in different device configurations. These results would provide new design rules for photonic structures in thin-film solar cells.
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88.40.jj Silicon solar cells
72.40.+w Photoconduction and photovoltaic effects

Optical bistability in a quantum dots/micropillar device with a quality factor exceeding 200 000

Christophe Arnold, Vivien Loo, Aristide Lemaître, Isabelle Sagnes, Olivier Krebs, Paul Voisin, Pascale Senellart, and Loïc Lanco

Appl. Phys. Lett. 100, 111111 (2012); http://dx.doi.org/10.1063/1.3694026 (3 pages) | Cited 5 times

Online Publication Date: 14 March 2012

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Optical bistability is demonstrated in a micropillar cavity with a record quality factor of 215 000, embedding a few thousand quantum dots. A power threshold of 380μW is obtained, with an on/off response contrast of 5.6 dB. We characterize the saturation of the quantum dots absorption and the cavity mode frequency shift through coherent reflection spectroscopy. We show that a near-unity coupling efficiency is achieved and that the planar quality factor Q0 is around 450 000.
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85.30.-z Semiconductor devices

Electric field detection of coherent synchrotron radiation in a storage ring generated using laser bunch slicing

I. Katayama, H. Shimosato, M. Bito, K. Furusawa, M. Adachi, M. Shimada, H. Zen, S. Kimura, N. Yamamoto, M. Hosaka, M. Katoh, and M. Ashida

Appl. Phys. Lett. 100, 111112 (2012); http://dx.doi.org/10.1063/1.3694049 (4 pages)

Online Publication Date: 14 March 2012

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The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile.
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29.27.Eg Beam handling; beam transport
29.20.db Storage rings and colliders

Quantifying the radiation efficiency of nano antennas

Yuval Yifat, Zeev Iluz, Michal Eitan, Inbal Friedler, Yael Hanein, Amir Boag, and Jacob Scheuer

Appl. Phys. Lett. 100, 111113 (2012); http://dx.doi.org/10.1063/1.3694278 (4 pages) | Cited 2 times

Online Publication Date: 14 March 2012

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The radiation efficiency of nano antennas is a critical parameter determining their suitability for various applications. To that end, the radiation efficiency of a single antenna is directly quantified using far-field measurements of the reflectance of an array comprising identical nano-antennas. Excellent agreement in terms of resonance frequencies, optical bandwidth, and scattering efficiency is found between the results of experimental measurements and finite element-based numerical analysis of scattering from Au nano-antenna arrays. Extremely high overall radiation efficiencies, exceeding 82%, are obtained. The high efficiency can facilitate the employment of such nano-antennas for applications in imaging, spectroscopy, and solar energy harvesting.
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84.40.Ba Antennas: theory, components and accessories
02.70.Dh Finite-element and Galerkin methods

Optical activity and coupling in twisted dimer meta-atoms

Mingkai Liu, David A. Powell, Ilya V. Shadrivov, and Yuri S. Kivshar

Appl. Phys. Lett. 100, 111114 (2012); http://dx.doi.org/10.1063/1.3694269 (4 pages) | Cited 2 times

Online Publication Date: 15 March 2012

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We analyse the optical activity in twisted dimers, the meta-atoms of a chiral metamaterial, by introducing a simple yet accurate model for the coupling between them. The near-field interaction coefficients are derived from a Lagrangian model and include the effects of retardation, whereas the far-field radiation is based on a multipole expansion. We show that the optimum twist angle varies with frequency, and near resonance is substantially lower than 45 degrees, which is the lowest symmetry configuration. Our approach is accurate over a wide frequency range, including the resonant regions with the highest optical activity. In contrast to other models of near-field interaction, it requires no fitted parameters or homogenization procedure and is directly applicable to a wide variety of resonant particles.
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33.55.+b Optical activity and dichroism
31.15.X- Alternative approaches

Simultaneous radiation pressure induced heating and cooling of an opto-mechanical resonator

Siddharth Tallur and Sunil A. Bhave

Appl. Phys. Lett. 100, 111115 (2012); http://dx.doi.org/10.1063/1.3694772 (4 pages) | Cited 1 time

Online Publication Date: 15 March 2012

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Cavity opto-mechanics enabled radiation-pressure coupling between optical and mechanical modes of a micro-mechanical resonator gives rise to dynamical backaction, enabling amplification and cooling of mechanical motion. Due to a combination of large mechanical oscillations and necessary saturation of amplification, the noise floor of the opto-mechanical resonator increases, rendering it ineffective at transducing small signals and thereby cooling another mechanical resonance of the system. Here, we show amplification of one mechanical resonance in a micro-mechanical ring resonator while simultaneously cooling another mechanical resonance by exploiting two closely spaced optical whispering gallery mode cavity resonances.
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85.60.-q Optoelectronic devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Polarization independent liquid crystal gratings based on orthogonal photoalignments

Wei Hu, Abhishek Kumar Srivastava, Xiao-Wen Lin, Xiao Liang, Zi-Jian Wu, Jia-Tong Sun, Ge Zhu, Vladimir Chigrinov, and Yan-Qing Lu

Appl. Phys. Lett. 100, 111116 (2012); http://dx.doi.org/10.1063/1.3694921 (4 pages) | Cited 10 times

Online Publication Date: 15 March 2012

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The polarization independence of liquid crystal gratings with alternate orthogonal aligned regions is theoritically studied and demonstrated by means of photoalignment technique. The different alignments in adjecent regions are achieved by two-step photo exposure to guide orientations of sulfonic azo dye layers and further align the liquid crystal molecules. Both one-dimensional and two-dimensional switchable phase gratings have been demonstrated. Such polarizer-free gratings show very high transmittance (∼92%), diffraction efficiency (over 31%), and optical contrast (over 150) including low power consumption.
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42.79.Dj Gratings
42.79.Kr Display devices, liquid-crystal devices

Temporal dynamics of all-optical switching in quadratic nonlinear directional couplers

R. Schiek, A. S. Solntsev, and D. N. Neshev

Appl. Phys. Lett. 100, 111117 (2012); http://dx.doi.org/10.1063/1.3696030 (4 pages) | Cited 2 times

Online Publication Date: 16 March 2012

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We study the temporal dynamics of all-optical switching in nonlinear directional couplers in periodically poled lithium niobate. The characteristic features of such switching, including asymmetric pulse break-up and back-switching were measured in full agreement with the theoretical predictions. Based on the time-resolved measurement of intensity-dependent switching, finally the theoretically long-known continuous-wave switching curve has experimentally been confirmed.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers

Suppression of electron overflow and efficiency droop in N-polar GaN green light emitting diodes

F. Akyol, D. N. Nath, S. Krishnamoorthy, P. S. Park, and S. Rajan

Appl. Phys. Lett. 100, 111118 (2012); http://dx.doi.org/10.1063/1.3694967 (4 pages) | Cited 6 times

Online Publication Date: 16 March 2012

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In this letter, we experimentally demonstrate direct correlation between efficiency droop and carrier overflow in InGaN/GaN green light emitting diodes (LEDs). Further, we demonstrate flat external quantum efficiency curve up to 400 A/cm2 in a plasma assisted molecular beam epitaxy grown N-polar double quantum well LED without electron blocking layers. This is achieved by exploring the superior properties of reverse polarization field of N-face polarity, such as effective carrier injection and higher potential barriers against carrier overflow mechanism. The LEDs were found to operate with a low (∼2.3 V) turn-on voltage.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Sz Deposition technology

Influence of barrier thickness on the performance of InGaN/GaN multiple quantum well solar cells

J. J. Wierer, Jr., D. D. Koleske, and S. R. Lee

Appl. Phys. Lett. 100, 111119 (2012); http://dx.doi.org/10.1063/1.3695170 (5 pages) | Cited 4 times

Online Publication Date: 16 March 2012

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The performance of InGaN/GaN multiple quantum well (MQW) solar cells containing 15 periods of 2.7 nm thick In0.21Ga0.79N wells and three different GaN barriers thicknesses of 3.0 nm, 6.3 nm, and 10.0 nm is investigated. Increasing barrier thickness results in absorption at lower energies, consistent with piezoelectric polarization induced electric fields tilting the energy bands of the MQW and changing the transition energy of well states. The internal quantum efficiency and leakage currents are additionally affected by GaN barrier thickness, resulting in the 6.3 nm barrier structure achieving the highest power conversion efficiency (1.66%, 1 sun AM1.5G).
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88.40.J- Types of solar cells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Study of the impedance mismatch at the output end of a THz parallel-plate waveguide

Marx Mbonye, Rajind Mendis, and Daniel M. Mittleman

Appl. Phys. Lett. 100, 111120 (2012); http://dx.doi.org/10.1063/1.3695329 (4 pages) | Cited 3 times

Online Publication Date: 16 March 2012

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We study the reflection of terahertz (THz) radiation at the end of a parallel-plate waveguide (PPWG), due to the impedance mismatch between the propagating transverse-electromagnetic mode and the free-space background. We find that, for a PPWG with uniformly spaced plates, the reflection coefficient at the output face increases as the plate separation decreases, consistent with predictions by early low frequency ray optical theory. We also study the reflection coefficient for tapered PPWGs where the plate spacing is tapered, for which no analytical theory exists, and quantify the reflection coefficient as a function of the plate separation and the THz frequency.
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42.79.Gn Optical waveguides and couplers
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