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13 Dec 2010

Volume 97, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 97, 241101 (2010); http://dx.doi.org/10.1063/1.3525583 (3 pages)

Kanghee Lee and Jaewook Ahn
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Single-pixel coherent diffraction imaging

Kanghee Lee and Jaewook Ahn

Appl. Phys. Lett. 97, 241101 (2010); http://dx.doi.org/10.1063/1.3525583 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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We demonstrate single-pixel coherent diffraction imaging, whereby broadband terahertz waveforms passed through a slanted phase retarder (SPR), diffracted from an object, were measured by a terahertz detector located in the far field. For one dimensional imaging, the fixed-location single-pixel broadband detector simultaneously measured all the spatial frequency components of the object because the frequency components of the source maintain a one-to-one correspondence with the object’s spatial frequency. For two dimensional imaging, the angular position of the SPR enabled the diffracted terahertz wave to carry an angular projection image of the object.
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84.40.Az Waveguides, transmission lines, striplines
02.30.-f Function theory, analysis

Direct band Ge photoluminescence near 1.6 μm coupled to Ge-on-Si microdisk resonators

Gary Shambat, Szu-Lin Cheng, Jesse Lu, Yoshio Nishi, and Jelena Vuckovic

Appl. Phys. Lett. 97, 241102 (2010); http://dx.doi.org/10.1063/1.3526732 (3 pages) | Cited 3 times

Online Publication Date: 13 December 2010

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We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium grown on silicon. Resonators coupled to fiber tapers display clear whispering gallery modes in transmission and photoluminescence with quality factors limited by germanium’s material absorption. Continuous wave pumping of the cavities resulted in a dominant heating effect for the cavity modes in both transmission and photoluminescence. Pulsed optical pumping proved to be more effective in minimizing heating, but was not sufficient to observe material gain or lasing. We believe that significantly higher doping levels are critical in order to achieve lasing at reasonable pump conditions.
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42.79.-e Optical elements, devices, and systems
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators

High harmonic generation spectroscopy of hydrocarbons

C. Vozzi, R. Torres, M. Negro, L. Brugnera, T. Siegel, C. Altucci, R. Velotta, F. Frassetto, L. Poletto, P. Villoresi, S. De Silvestri, S. Stagira, and J. P. Marangos

Appl. Phys. Lett. 97, 241103 (2010); http://dx.doi.org/10.1063/1.3526752 (3 pages) | Cited 1 time

Online Publication Date: 15 December 2010

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We have demonstrated the ability of few-cycle midinfrared intense laser pulses to produce extended harmonic spectra ( ≥ 45 eV) suitable for high harmonic spectroscopy in aligned hydrocarbons with ionization potentials in the range 9.07–11.52 eV. Modulations in the spectra measured with different alignment angles show signatures of the molecular structure. These results pave the way for the extension of high harmonic spectroscopy to complex biomolecules.
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33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.80.Eh Autoionization, photoionization, and photodetachment

Photon spin-to-orbital angular momentum conversion via an electrically tunable q-plate

Bruno Piccirillo, Vincenzo D’Ambrosio, Sergei Slussarenko, Lorenzo Marrucci, and Enrico Santamato

Appl. Phys. Lett. 97, 241104 (2010); http://dx.doi.org/10.1063/1.3527083 (3 pages)

Online Publication Date: 16 December 2010

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Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retardation of liquid-crystal-based q-plates through an externally applied voltage. Electro-optic q-plates can be operated as electrically driven converters of photon spin into orbital angular momentum, enabling a variation of the orbital angular momentum probabilities of the output photons over a time scale of milliseconds.
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61.30.-v Liquid crystals
78.20.Jq Electro-optical effects

Carrier lifetime in erbium-doped GaN waveguide emitting in 1540 nm wavelength

Q. Wang, R. Hui, R. Dahal, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 97, 241105 (2010); http://dx.doi.org/10.1063/1.3527089 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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We report the characteristics of an erbium-doped GaN semiconductor waveguide amplifier grown by metal-organic chemical vapor deposition. We demonstrated that both 980 and 1480 nm optical pumping were efficient to create population inversion between the 4I13/2 and 4I15/2 energy levels. The carrier lifetime in the 4I13/2 energy band was measured to be approximately 1.5 ms in room temperature, which is slightly shorter than that in erbium-doped silica due to the interaction between the erbium ions and the semiconductor lattice structure. But it is significantly longer than the carrier lifetime in a typical semiconductor optical amplifier which is in the nanosecond regime.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Silver halide planar waveguides and grating couplers for middle infrared integrated optics

B. Dekel and A. Katzir

Appl. Phys. Lett. 97, 241106 (2010); http://dx.doi.org/10.1063/1.3527920 (3 pages)

Online Publication Date: 16 December 2010

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We fabricated silver bromide (AgBr) planar waveguides with a thickness of ≈ 20 μm and designed reflective grating couplers for coupling the radiation of a tunable CO2 laser into these waveguides. We found that the attenuation was 6–9 dB/cm. The waveguides were used as attenuated total reflection elements for the sensing of hazardous pesticides in water in concentrations higher than 25 ppm. This work will pave the way for developing integrated optical elements and circuits which are based on silver halides and which operate in a broad spectral range in the mid-IR. These will be useful as chemical sensors and as spatial elements in nulling interferometry.
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42.82.Et Waveguides, couplers, and arrays
42.79.Dj Gratings
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

ZnO random laser diode arrays for stable single-mode operation at high power

H. K. Liang, S. F. Yu, and H. Y. Yang

Appl. Phys. Lett. 97, 241107 (2010); http://dx.doi.org/10.1063/1.3527922 (3 pages) | Cited 3 times

Online Publication Date: 16 December 2010

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An array of highly disordered i-ZnO:Al(3%) random cavities, which have 1 μm width, 150 nm thickness, and 2 mm length, is sandwiched between n-ZnO:Al(5%) and p-GaN/sapphire substrate to form an array of heterojunctions. The random cavities, which are electrically isolated and optically coupled with the adjacent random cavities, are laterally separated by a 1 μm wide Al2O3 dielectric insulator. Stable single-mode operation is observed from the laser diode array under high electrical pumping (i.e., >6×threshold current) at room temperature.
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42.55.Px Semiconductor lasers; laser diodes

Strong influence of packing density in terahertz metamaterials

Ranjan Singh, Carsten Rockstuhl, and Weili Zhang

Appl. Phys. Lett. 97, 241108 (2010); http://dx.doi.org/10.1063/1.3525169 (3 pages) | Cited 2 times

Online Publication Date: 16 December 2010

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We investigate the response of a terahertz metamaterial depending on the unit cell density. The fundamental inductive capacitive (LC) resonance has its highest quality (Q) factor for a critical period Pc = λ/n, with λ being the LC resonance wavelength and n being the refractive index of the substrate. This occurs due to simultaneous excitation of the lowest order lattice mode that strongly favors radiative coupling in the metamaterial plane. Increasing or decreasing the period from Pc reduces the Q factor. Our results suggest that an optimal package density exists in metamaterials to induce the strongest dispersion.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High-resolution wide-field standing-wave surface plasmon resonance fluorescence microscopy with optical vortices

P. S. Tan, X.-C. Yuan, G. H. Yuan, and Q. Wang

Appl. Phys. Lett. 97, 241109 (2010); http://dx.doi.org/10.1063/1.3525173 (3 pages)

Online Publication Date: 16 December 2010

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A technique for high-resolution wide-field fluorescence microscopy by using standing surface plasmon waves induced by optical vortices (OVs) is proposed, aiming at harnessing its unique dynamic properties to sequentially illuminate specimen with different phase-shifted interference excitation field. Topological charges of the OV are employed to modulate phase-shifting of the interference pattern. Numerical studies and experimental results reveal an achievement of 0.25λ optical resolution, a factor of twofold improvement compared with the standard total-internal-reflection fluorescence microscopy.
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07.60.Pb Conventional optical microscopes
07.60.Ly Interferometers

Quantum dot-cavity strong-coupling regime measured through coherent reflection spectroscopy in a very high-Q micropillar

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

Appl. Phys. Lett. 97, 241110 (2010); http://dx.doi.org/10.1063/1.3527930 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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We report on the coherent reflection spectroscopy of a high-quality factor micropillar, in the strong-coupling regime with a single InGaAs annealed quantum dot. The absolute reflectivity measurement is used to study the characteristics of the device at low and high excitation powers. The strong coupling is obtained with a g = 16 μeV coupling strength in a 7.3 μm diameter micropillar, with a cavity spectral width κ = 20.5 μeV (Q = 65 000). The factor of merit of the strong-coupling regime, 4g/κ = 3, is the current state-of-the-art for a quantum dot-micropillar system.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
81.40.Gh Other heat and thermomechanical treatments
78.67.Hc Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing

Highly efficient yellow photoluminescence from {11–22} InGaN multiquantum-well grown on nanoscale pyramid structure

Taek Kim, Joosung Kim, Moon-Seung Yang, Sangmoon Lee, Youngsoo Park, U-In Chung, and Yonghoon Cho

Appl. Phys. Lett. 97, 241111 (2010); http://dx.doi.org/10.1063/1.3524524 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2010

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InGaN/GaN multiquantum wells (MQWs) with a peak wavelength of 570 nm are grown on nanosize GaN hexagonal pyramid structures. Temperature dependent photoluminescence (PL) measurements from 10 to 300 K show a high integrated intensity ratio of 0.45. The emission energy of the MQW monotonically decreases with temperature increase, showing the absence of localized potential. Power dependent PL shows no noticeable blueshift caused by piezoelectric field screening effect. Comparative study of the PL results with those of the InGaN MQW on microsize pyramid show that nanosize pyramids play an important role in suppressing piezoelectric field in addition to the semipolar growth direction. We attribute the high luminescence efficiency of the MQW on nanosize pyramid structures to effectively suppressed piezoelectric field and potential localization.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
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