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13 Feb 2012

Volume 100, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 073501 (2012); http://dx.doi.org/10.1063/1.3682479 (3 pages)

S. Tongay, M. Lemaitre, J. Fridmann, A. F. Hebard, B. P. Gila, and B. R. Appleton
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Terahertz composite right-left handed transmission-line metamaterial waveguides

Zhijun Liu, Philip W. C. Hon, Amir A. Tavallaee, Tatsuo Itoh, and Benjamin S. Williams

Appl. Phys. Lett. 100, 071101 (2012); http://dx.doi.org/10.1063/1.3684250 (4 pages) | Cited 2 times

Online Publication Date: 13 February 2012

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We report terahertz metamaterial waveguides based on the concept of composite right/left-handed transmission-lines. The waveguides are implemented in a metal-insulator-metal geometry fabricated with spin-coated Benzocyclobutene and contact photolithography. Angle-resolved reflection spectroscopy shows strong resonant absorption features corresponding to both right-handed and left-handed (backward wave) propagating modes within the leaky-wave bandwidth. Tuning of the waveguide dispersion is achieved by varying the effective lumped element series capacitance. The experimental results are in good agreement with full-wave finite element method simulations as well as an intuitive transmission-line circuit model.
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42.79.Gn Optical waveguides and couplers

Multiplexing single-beam coherent anti-stokes Raman spectroscopy with heterodyne detection

Alexander Wipfler, Tiago Buckup, and Marcus Motzkus

Appl. Phys. Lett. 100, 071102 (2012); http://dx.doi.org/10.1063/1.3680209 (4 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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Multiplex detection of single beam coherent anti-Stokes Raman spectra is achieved by phase shaping of a narrow gate probe. The spectrally resolved signal is amplified via a local oscillator derived from the same single beam and is disentangled via double quadrature spectral interferometry. Spectral resolution and spectral range are defined by the width and position of the phase gate, which can be easily set by a femtosecond pulse shaper. Such phase-only multiplexed single beam coherent anti-Stokes Raman spectroscopy is demonstrated for simple molecules and is combined with Raman line reconstruction methods to obtain dispersion free Raman resonances.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Ly Interferometers

High quality factor two dimensional GaN photonic crystal cavity membranes grown on silicon substrate

N. Vico Triviño, G. Rossbach, U. Dharanipathy, J. Levrat, A. Castiglia, J.-F. Carlin, K. A. Atlasov, R. Butté, R. Houdré, and N. Grandjean

Appl. Phys. Lett. 100, 071103 (2012); http://dx.doi.org/10.1063/1.3684630 (3 pages) | Cited 8 times

Online Publication Date: 14 February 2012

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We report on the achievement of freestanding GaN photonic crystal L7 nanocavities with embedded InGaN/GaN quantum wells grown by metal organic vapor phase epitaxy on Si (111). GaN was patterned by e-beam lithography, using a SiO2 layer as a hard mask, and usual dry etching techniques. The membrane was released by underetching the Si (111) substrate. Micro-photoluminescence measurements performed at low temperature exhibit a quality factor as high as 5200 at ∼420 nm, a value suitable to expand cavity quantum electrodynamics to the near UV and the visible range and to develop nanophotonic platforms for biofluorescence spectroscopy.
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81.16.Nd Micro- and nanolithography
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Understanding ultrafast carrier dynamics in single quasi-one-dimensional Si nanowires

M. A. Seo, S. A. Dayeh, P. C. Upadhya, J. A. Martinez, B. S. Swartzentruber, S. T. Picraux, A. J. Taylor, and R. P. Prasankumar

Appl. Phys. Lett. 100, 071104 (2012); http://dx.doi.org/10.1063/1.3685487 (5 pages) | Cited 9 times

Online Publication Date: 15 February 2012

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We use femtosecond optical pump-probe spectroscopy to study ultrafast carrier dynamics in single quasi-one-dimensional silicon nanowires. By isolating individual nanowires, we avoid complications resulting from the broad size and alignment distribution in nanowire ensembles, allowing us to directly probe ultrafast carrier dynamics. Spatially-resolved experiments demonstrate the influence of surface-mediated mechanisms on carrier dynamics in a single NW, while polarization-resolved experiments reveal a clear anisotropy in carrier lifetimes measured parallel and perpendicular to the long axis of the NW, due to density-dependent Auger recombination. These results suggest the possibility of tailoring carrier relaxation in a single nanowire for a desired application.
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78.47.J- Ultrafast spectroscopy (<1 psec)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.20.Fv Electron impact: Auger emission

Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films

Zuanming Jin, Yue Xu, Zhengbing Zhang, Gaofang Li, Xian Lin, Guohong Ma, Zhenxiang Cheng, and Xiaolin Wang

Appl. Phys. Lett. 100, 071105 (2012); http://dx.doi.org/10.1063/1.3685496 (4 pages) | Cited 2 times

Online Publication Date: 15 February 2012

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The electronic energy relaxation of polycrystalline BiFeO3 films is studied using ultrafast pump-probe spectroscopy. After photo-excitation with femtosecond laser pulses, the relaxation of hot electrons is identified to decay with two different characteristic times. The fast process is attributed to scattering of electrons with lattice-vibration modes, and the slow one is corresponding to the spin-lattice thermalization. The electron-phonon coupling is characterized by the second moment of the Eliashberg function, λ〈ω2〉. Due to the structural strain and symmetry breaking, the electron-phonon interaction strength of tetragonal BiFeO3 films is larger than that of rhombohedral counterparts.
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73.61.Ng Insulators
78.66.Nk Insulators
73.50.Fq High-field and nonlinear effects
63.20.kd Phonon-electron interactions
77.55.Nv Multiferroic/magnetoelectric films
77.80.-e Ferroelectricity and antiferroelectricity

Fiber delivered two-color picosecond source through nonlinear spectral transformation for coherent Raman scattering imaging

Ke Wang and Chris Xu

Appl. Phys. Lett. 100, 071106 (2012); http://dx.doi.org/10.1063/1.3686149 (3 pages)

Online Publication Date: 16 February 2012

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We demonstrate a two-color, fiber-delivered picosecond source for coherent Raman scattering (CRS) imaging through nonlinear spectral transformation. The wavelength tunable picosecond pump is generated by nonlinear spectral compression of a prechirped femtosecond pulse in a fiber wavelength division multiplexer (WDM). The 1064-nm synchronized picosecond Stokes pulse is generated through pulse carving of a continuous wave laser, nonlinear spectral broadening in 100-m standard single-mode fiber, and subsequent dispersive compression with a fiber compressor. The pump and Stokes beams are combined and delivered by the fiber WDM. CRS imaging of mouse skin is performed to demonstrate the practicality of this source.
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42.55.Wd Fiber lasers
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Ultrafast response of tunnel injected quantum dot based semiconductor optical amplifiers in the 1300 nm range

J. Pulka, T. Piwonski, G. Huyet, J. Houlihan, E. Semenova, A. Lematre, K. Merghem, A. Martinez, and A. Ramdane

Appl. Phys. Lett. 100, 071107 (2012); http://dx.doi.org/10.1063/1.3686901 (4 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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The ultrafast gain and refractive index dynamics of tunnel injected quantum dot based semiconductor optical amplifiers in the 1300 nm range are investigated using a heterodyne pump probe technique. In the gain regime, ground state wavelengths exhibit full gain recovery in less than 10 ps up to 3 times transparency, attributed to enhanced carrier refilling via the injector layer. The effect of the injector can also been seen in unusual phase dynamics at excited state wavelengths at this injection level.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Four-wave mixing in carbon nanotube-coated optical fiber gratings

Li-Yang Shao, Michael B. Jakubinek, Tingting Sun, Benoit Simard, and Jacques Albert

Appl. Phys. Lett. 100, 071108 (2012); http://dx.doi.org/10.1063/1.3687170 (3 pages)

Online Publication Date: 16 February 2012

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The observation of four-wave mixing (FWM) in single-walled carbon nanotubes (SWCNTs) deposited around a tilted fiber Bragg grating (TFBG) has been demonstrated. A thin, floating SWCNT film is manually wrapped around the outer cladding of the fiber and FWM occurs between two core-guided laser signals by TFBG-induced interaction of the core mode and cladding modes. The effective nonlinear coefficient is calculated to be 1.8 × 103 W−1 Km−1. The wavelength of generated idlers is tunable with a range of 7.8 nm.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.81.Bm Fabrication, cladding, and splicing

Spin Hall effect of reflected light from an air-glass interface around the Brewster’s angle

Ling-Jun Kong (孔令军), Xi-Lin Wang (汪喜林), Si-Min Li, Yongnan Li (李勇男), Jing Chen, Bing Gu (顾兵), and Hui-Tian Wang (王慧田)

Appl. Phys. Lett. 100, 071109 (2012); http://dx.doi.org/10.1063/1.3687186 (3 pages) | Cited 2 times

Online Publication Date: 16 February 2012

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We have developed a modified theory of the spin Hall effect of reflected light from a planar interface composed of two dielectric media and obtain the analytical expression valid for any incident angle including the Brewster’s angle. We improved the experimental method and measured the spin-dependent transverse displacement of reflected light from a planar air-glass interface around the Brewster’s angle. The experimental results are in agreement with the theoretical prediction.
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72.25.-b Spin polarized transport

Electrically switchable random to photonic band-edge laser emission in chiral nematic liquid crystals

Stephen M. Morris, Damian J. Gardiner, Philip J. W. Hands, Malik M. Qasim, Timothy D. Wilkinson, Ian H. White, and Harry J. Coles

Appl. Phys. Lett. 100, 071110 (2012); http://dx.doi.org/10.1063/1.3684804 (3 pages) | Cited 1 time

Online Publication Date: 17 February 2012

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Using a chiral nematic liquid crystal with a negative dielectric anisotropy, it is possible to switch between band-edge laser emission and random laser emission with an electric field. At low frequencies (<1 kHz), random laser emission is observed as a result of scattering due to electro-hydrodynamic instabilities. However, band-edge laser emission is found to occur at higher frequencies (>5 kHz), where the helix is stabilized due to dielectric coupling. These results demonstrate a method by which the linewidth of the laser source can be readily controlled externally (from 4 nm to 0.5 nm) using electric fields.
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42.55.-f Lasers
42.70.Hj Laser materials
42.70.Df Liquid crystals

A statistical exploration of multiple exciton generation in silicon quantum dots and optoelectronic application

W. A. Su and W. Z. Shen

Appl. Phys. Lett. 100, 071111 (2012); http://dx.doi.org/10.1063/1.3687184 (5 pages) | Cited 3 times

Online Publication Date: 17 February 2012

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We have carried out an investigation of multiple exciton generation (MEG) in Si quantum dots (QDs) and its application in optoelectronic devices. A simple yet effective statistical model has been proposed based on Fermi statistical theory and impact ionization mechanism. It is demonstrated that the MEG efficiency depends on both the radius of Si QDs and the energy of incident photons, with the MEG threshold energy in the range of ∼2.2–3.1 Eg depending on the dot radius. While limited improvement has been observed in power conversion efficiency of single stage solar cells, MEG in Si QDs exhibits prospective for application in ultraviolet detectors due to the high internal quantum efficiency under short incident light.
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71.35.-y Excitons and related phenomena
73.21.La Quantum dots
88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells
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