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7 Nov 2005

Volume 87, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 192502 (2005); http://dx.doi.org/10.1063/1.2128478 (3 pages)

Ki-Suk Lee, SangKook Choi, and Sang-Koog Kim
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Photonic crystal templates for organic solid-state lasers

Shiyoshi Yokoyama, Tatsuo Nakahama, Shinro Mashiko, Masashi Nakao, Motohiro Yamada, Kazuyuki Nishio, and Hideki Masuda

Appl. Phys. Lett. 87, 191101 (2005); http://dx.doi.org/10.1063/1.2119428 (3 pages) | Cited 3 times

Online Publication Date: 31 October 2005

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We report a solid-state laser composed of an Al2O3 photonic crystal and an organic gain medium. The photonic crystal was fabricated through the nanoimprinting technique and an electrochemical process, which enables transfer of a periodic pattern to the photonic crystal and control of its stop band. When the photonic crystal was infiltrated with the polymer medium containing laser dye, we obtained laser emission under optical excitation. The minimum laser threshold was about 2.4 nJ/pulse, where the linewidth of the laser emission was as narrow as 0.09 nm. We explain the laser action based on the band edge effect, while the precise control of the laser mode and oscillation wavelength depends on control of the stop band and small changes in the refractive index of the gain medium.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
81.16.Nd Micro- and nanolithography
82.45.-h Electrochemistry and electrophoresis

Intersubband photoconductivity at 1.6 μm using a strain-compensated AlN/GaN superlattice

E. Baumann, F. R. Giorgetta, D. Hofstetter, H. Lu, X. Chen, W. J. Schaff, L. F. Eastman, S. Golka, W. Schrenk, and G. Strasser

Appl. Phys. Lett. 87, 191102 (2005); http://dx.doi.org/10.1063/1.2126130 (3 pages) | Cited 19 times

Online Publication Date: 31 October 2005

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We report on intersubband absorption, photovoltaic, and photoconductive detection of near-infrared radiation in regular AlN/GaN superlattice structures. Photoconductive detection was achieved up to temperatures of 120 K. Simulation of the transition energies using a self-consistent Schrödinger-Poisson equation solver for our specific well width is in good agreement with the measurements. For a well width of 17 Å, the transition energy between ground state and first excited state in the GaN well is around 6300 cm−1 which corresponds to 1.6 μm.
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73.50.Pz Photoconduction and photovoltaic effects
73.21.Cd Superlattices
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Ring and axis mode switching in multielectrode strained InGaAsP multiple-quantum-well quasistadium laser diodes

Takehiro Fukushima, Tomoko Tanaka, and Takahisa Harayama

Appl. Phys. Lett. 87, 191103 (2005); http://dx.doi.org/10.1063/1.2126143 (3 pages) | Cited 3 times

Online Publication Date: 31 October 2005

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We describe the mode switching operation of multielectrode strained InGaAsP multiple-quantum-well quasistadium laser diodes. Far-field patterns exhibit highly directional emission along the laser cavity axis for current injection at the axis electrode and highly directional emission at angles ±19° from the cavity axis for current injection at the ring electrode. These directions correspond to the axis mode and the ring trajectory mode of the laser cavity. We also succeeded in obtaining single peak output beams using narrow curved end mirrors of 40 μm width.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Terahertz radiation from nonstoichiometric CuInSe2 films excited by femtosecond laser pulses

R. Adomavičius, A. Krotkus, J. Kois, S. Bereznev, and E. Mellikov

Appl. Phys. Lett. 87, 191104 (2005); http://dx.doi.org/10.1063/1.2126796 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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We report on the observation of efficient terahertz radiation from the surface of CuInSe2 excited by femtosecond laser pulses. Terahertz radiation emitted by polycrystalline CuInSe2 layers manufactured by using electrodeposition technology was as powerful as the signals radiated by single-crystalline semiconductor surfaces. It has been found that terahertz radiation efficiency is critically dependent on the stoichiometry of the CuInSe2 layers. The results of a double-pulse excitation experiment have indicated that terahertz radiation from the photoexcited surfaces of CuInSe2 samples was caused by the presence of a built-in electrical field at those surfaces.
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78.70.Gq Microwave and radio-frequency interactions
78.66.Li Other semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.66.Bi Elemental solids
61.66.Dk Alloys

Emission properties of an organic light-emitting diode patterned by a photoinduced autostructuration process

C. Hubert, C. Fiorini-Debuisschert, I. Hassiaoui, L. Rocha, P. Raimond, and J.-M. Nunzi

Appl. Phys. Lett. 87, 191105 (2005); http://dx.doi.org/10.1063/1.2126793 (3 pages) | Cited 8 times

Online Publication Date: 31 October 2005

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The photoluminescence properties of a periodically structured organic light-emitting diode are presented. Patterning is achieved using an original single-step autostructuration technique based on photoinduced effects in azo-polymer films. We show that single beam laser irradiation can lead to the induction of regular two-dimensional surface relief gratings. The waveguide properties of these microstructures as well as their effect on the emission properties of a light-emitting material are studied. We demonstrate a new straightforward technique to improve external light emission efficiency by outcoupling part of the light that was initially guided into the different diode layers.
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85.60.Jb Light-emitting devices

Polarization-independent phase modulation of a homeotropic liquid crystal gel

Hongwen Ren, Yi-Hsin Lin, Chien-Hui Wen, and Shin-Tson Wu

Appl. Phys. Lett. 87, 191106 (2005); http://dx.doi.org/10.1063/1.2126107 (3 pages) | Cited 9 times

Online Publication Date: 1 November 2005

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A homeotropic liquid crystal (LC) gel with submicron domain size is fabricated and its phase-only modulation property evaluated. The LC gel is highly transparent in the voltage-off state and exhibits pure phase modulation before light scattering occurs. Compared to a nanosized polymer-dispersed liquid crystal (nano-PDLC), our gel possesses a larger phase change but at a lower operating voltage because of a higher LC concentration. Similar to a nano-PDLC, our gel also exhibit submillisecond response time, hysteresis-free, and polarization-independent phase change.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals
82.70.Gg Gels and sols

Characterization of a 90° waveguide bend using near-field scanning optical microscopy

Guangwei Yuan, Kevin L. Lear, Matthew D. Stephens, and David S. Dandy

Appl. Phys. Lett. 87, 191107 (2005); http://dx.doi.org/10.1063/1.2126135 (3 pages) | Cited 3 times

Online Publication Date: 1 November 2005

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Multiple modes are directly imaged in a silicon nitride waveguide bend using near-field scanning optical microscopy. Since the high order mode attenuates faster than the fundamental mode, a transient interference is observed. Local loss at the bend-to-straight waveguide interface is found and attributed to modal mismatch. The observations are in good agreement with modal calculations using conformal index transformation.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

In situ formation of a gel microbead for indirect laser micromanipulation of microorganisms

Akihiko Ichikawa, Fumihito Arai, Keiichi Yoshikawa, Tomoyuki Uchida, and Toshio Fukuda

Appl. Phys. Lett. 87, 191108 (2005); http://dx.doi.org/10.1063/1.2126800 (3 pages) | Cited 2 times

Online Publication Date: 1 November 2005

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We propose the in situ formation of gel microbeads made of a thermoreversible hydrogel for indirect laser micromanipulation of microorganisms. Irradiation, using a 1064 nm laser, of an aqueous solution mixed with poly-(N-isopropylacrylamide) through a high magnification lens resulted in the formation of a gel microbead at the laser focus due to heating. The gel microbead is trapped by the laser, and is used for indirect laser micromanipulation of microorganisms. However, the laser power used to form the bead is generally too strong to perform manipulation in a stable manner. In this letter we show a method to reduce the laser power to form a gel microbead using the poly-(N-isopropylacrylamide) aqueous solution by the addition of additives. The gelation temperature and the laser absorption rate of the solution in the presence of several different additives were investigated. We selected YPD (yeast extract, peptone, dextrose) broth as an additive and measured the relationship between the laser power, irradiation time, and diameter of the gel microbead. We succeeded in reducing the laser power for gel microbead formation, and in using the laser-trapped gel microbead for the manipulation of a yeast cell and DNA.
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87.80.-y Biophysical techniques (research methods)
87.16.-b Subcellular structure and processes
82.70.Gg Gels and sols
42.62.Be Biological and medical applications
87.14.G- Nucleic acids

Achieving superresolution in near-field optical data readout systems using surface plasmons

Greg Gbur, Hugo F. Schouten, and Taco D. Visser

Appl. Phys. Lett. 87, 191109 (2005); http://dx.doi.org/10.1063/1.2128061 (3 pages) | Cited 20 times

Online Publication Date: 1 November 2005

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The effects of surface plasmons and enhanced transmission on the readout contrast in a superresolving near-field optical data system are studied numerically using an exact Green’s tensor formulation. It is shown that plasmon effects can both help and hinder such a readout system, and the system geometry must be chosen carefully to produce optimal effects. Under certain conditions, the system can have a readout contrast approaching 50% and a resolution of at least λ/3.
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42.79.Vb Optical storage systems, optical disks
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Second-harmonic generation in hydrogenated amorphous-Si1−xNx doubly resonant microcavities with periodic dielectric mirrors

S. Lettieri, F. Gesuele, P. Maddalena, M. Liscidini, L. C. Andreani, C. Ricciardi, V. Ballarini, and F. Giorgis

Appl. Phys. Lett. 87, 191110 (2005); http://dx.doi.org/10.1063/1.2125112 (3 pages) | Cited 4 times

Online Publication Date: 4 November 2005

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We report on the realization of microcavities made of hydrogenated amorphous-Si1−xNx multilayers, with dual-wavelength periodic dielectric mirrors in order to obtain first and second order stop bands. Optical second-harmonic generation with simultaneous resonance for the pump and harmonic waves is demonstrated at finite values of the angle of incidence. The results are in good agreement with a theoretical calculation of the harmonic generation process based on a nonlinear polarization localized at the interfaces between different amorphous layers.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Bh Lenses, prisms and mirrors

Electro-optic modulation using single-crystal film of an organic molecular salt in a Fabry-Perot cavity

S. P. Kutty and M. Thakur

Appl. Phys. Lett. 87, 191111 (2005); http://dx.doi.org/10.1063/1.2130394 (3 pages) | Cited 2 times

Online Publication Date: 4 November 2005

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Electro-optic modulation using single-crystal film of an organic molecular salt placed in a Fabry-Perot cavity has been measured at 633 and 750 nm. Large modulation depth (80%) at a low applied field (0.5 V/μm) has been observed in the field-induced birefringence geometry (mirror reflectivity ∼ 70%) for a bias point which was controlled by moving one of the mirrors. A modulation of about 60% with a higher throughput was obtained when no analyzer was used and the incident polarization was parallel to the dipole-axis.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Wc Optical coatings
42.79.Bh Lenses, prisms and mirrors

Three-dimensional optical tomographic imaging of scattering objects in tissue-simulating turbid media using independent component analysis

M. Alrubaiee, M. Xu, S. K. Gayen, M. Brito, and R. R. Alfano

Appl. Phys. Lett. 87, 191112 (2005); http://dx.doi.org/10.1063/1.2130547 (3 pages) | Cited 7 times

Online Publication Date: 4 November 2005

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An information-theory-based approach for the detection and three-dimensional localization of scattering targets embedded in a turbid medium, such as a tumor in the breast, is introduced. The approach uses multisource illumination of the medium, multidetector transillumination signal acquisition, and independent component analysis of the information theory for target detection and localization. The efficacy of the approach is demonstrated by detecting and obtaining location information about scattering targets embedded in human breast tissue-simulating turbid media of thickness 50 times the transport mean-free path.
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87.63.L- Visual imaging
02.50.-r Probability theory, stochastic processes, and statistics
89.70.-a Information and communication theory

Out-of-plane dispersion and homogenization in photonic crystal slabs

Zhongping Jian and Daniel M. Mittleman

Appl. Phys. Lett. 87, 191113 (2005); http://dx.doi.org/10.1063/1.2131195 (3 pages) | Cited 12 times

Online Publication Date: 4 November 2005

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We report a measurement of out-of-plane dispersion in two-dimensional photonic crystal slabs. Using terahertz time-domain spectroscopy, we obtain the complex transmission coefficient over a broad spectrum, ranging from the long wavelength (homogeneous) limit up to beyond the first few guided resonances. Despite the absence of a band gap, the out-of-plane dispersion is significant and in addition exhibits a complicated spectral dependence. Calculations of the effective refractive index which assume translational invariance in the direction perpendicular to the slab are in only approximate agreement with the measured homogeneous effective index and dispersion. In contrast, numerical simulations which accurately account for the finite slab thickness give much more accurate predictions.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions
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