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6 Feb 2006

Volume 88, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 063509 (2006); http://dx.doi.org/10.1063/1.2171834 (3 pages)

M. Feng, N. Holonyak, R. Chan, A. James, and G. Walter
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Efficient 3-μm difference frequency generation using direct-bonded quasi-phase-matched LiNbO3 ridge waveguides

Osamu Tadanaga, Tsutomu Yanagawa, Yoshiki Nishida, Hiroshi Miyazawa, Katsuaki Magari, Masaki Asobe, and Hiroyuki Suzuki

Appl. Phys. Lett. 88, 061101 (2006); http://dx.doi.org/10.1063/1.2172400 (3 pages) | Cited 28 times

Online Publication Date: 6 February 2006

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We fabricate 50-mm-long direct-bonded quasi-phase-matched LiNbO3 ridge waveguides for difference frequency generation in the 3-μm wavelength range. Conversion efficiency of 40%/W is achieved using a 1-μm-band pump and a 1.55-μm-band signal, and a 0.26-mW output is obtained. We also use the device to demonstrate methane gas detection at around 3.3 μm.
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42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Wi Nonlinear waveguides
42.86.+b Optical workshop techniques
82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.70.Mp Nonlinear optical crystals

Room temperature slow and fast light in quantum-dot semiconductor optical amplifiers

Hui Su and Shun Lien Chuang

Appl. Phys. Lett. 88, 061102 (2006); http://dx.doi.org/10.1063/1.2171652 (3 pages) | Cited 43 times

Online Publication Date: 6 February 2006

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We demonstrate room temperature optically and electrically controllable group delay using population oscillation in a quantum-dot (QD) semiconductor optical amplifier (SOA). A reduction of the group index up to 10% with a bandwidth of 13 GHz is achieved under different configurations of injection current and optical pump intensity. Our theoretical results based on population pulsation agree well with experimental data. We extract the linewidth enhancement factor and effective carrier diffusion coefficient of the QD SOA. We also observe slow light when the injection current is increased.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Electrical modulation of silicon-based two-dimensional photonic bandgap structures

M. Haurylau, S. P. Anderson, K. L. Marshall, and P. M. Fauchet

Appl. Phys. Lett. 88, 061103 (2006); http://dx.doi.org/10.1063/1.2172070 (3 pages) | Cited 20 times

Online Publication Date: 6 February 2006

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Electrically tunable photonic band gap (PBG) structures hold the potential to become a versatile and compact backbone for optical signal processing. In this letter we report electrical tuning of silicon-based two-dimensional PBG structures infiltrated with liquid crystals. An improved electrode configuration is used to avoid electric field screening by the conductive silicon walls. Electrical tuning using fields well below 1 V/μm is demonstrated experimentally using both polarized light microscopy and reflectance PBG measurements. The structures can be operated with any electro-optic materials and lead to fast and efficient modulators, routers, and tunable filters.
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42.70.Qs Photonic bandgap materials
78.20.Jq Electro-optical effects

Low-temperature InP/GaAs wafer bonding using sulfide-treated surface

Hui Huang, Xiaomin Ren, Xinyan Wang, Qi Wang, and Yongqing Huang

Appl. Phys. Lett. 88, 061104 (2006); http://dx.doi.org/10.1063/1.2172024 (3 pages) | Cited 4 times

Online Publication Date: 7 February 2006

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An approach for InP/GaAs wafer bonding based on thiourea treatment was presented. The bonding energy reaches the InP fracture energy by annealing at 360 °C. An In0.53Ga0.47As/InP multiple quantum well (MQW) structure grown on InP was transferred onto GaAs substrate via the bonding process. X-ray diffraction and photoluminescence reveal that crystal quality of the bonded MQW was preserved. A thin sulfide layer with thickness of about 29 nm at the bonding interface was detected. X-ray photoelectron spectroscopy analyses indicate that the formation of In–S and Ga–S bond at thiourea treated surface is responsible for the strong fusion obtained at such low temperature.
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81.65.-b Surface treatments
61.72.Cc Kinetics of defect formation and annealing
78.67.De Quantum wells
78.55.Cr III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Polariton quantum boxes in semiconductor microcavities

O. El Daïf, A. Baas, T. Guillet, J.-P. Brantut, R. Idrissi Kaitouni, J. L. Staehli, F. Morier-Genoud, and B. Deveaud

Appl. Phys. Lett. 88, 061105 (2006); http://dx.doi.org/10.1063/1.2172409 (3 pages) | Cited 47 times

Online Publication Date: 7 February 2006

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We report on the realization of polariton quantum boxes in a semiconductor microcavity under strong coupling regime. The quantum boxes consist of mesas, etched on the top of the spacer of a microcavity, that confine the cavity photon. For mesas with sizes of the order of a few microns in width and nanometers in depth, we observe quantization of the polariton modes in several states, caused by the lateral confinement. We evidence the strong exciton-photon coupling regime through a typical anticrossing curve for each quantized level. Moreover, the growth technique permits one to obtain high-quality samples, and opens the way for the conception of new optoelectronic devices.
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78.67.Hc Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Phase-conjugate mirror via two-photon thermal light imaging

Giuliano Scarcelli, Vincenzo Berardi, and Yanhua Shih

Appl. Phys. Lett. 88, 061106 (2006); http://dx.doi.org/10.1063/1.2172410 (3 pages) | Cited 43 times

Online Publication Date: 7 February 2006

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We report on a two-photon imaging experiment in which a thermal light source behaves like a phase-conjugate mirror, which produces a real image of an object. The result offers a novel scheme of imaging and thus suggests useful applications.
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42.79.Bh Lenses, prisms and mirrors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Pw Imaging detectors and sensors

Low-threshold and narrow-linewidth lasing from dye-doped holographic polymer-dispersed liquid crystal transmission gratings

Y. J. Liu, X. W. Sun, P. Shum, H. P. Li, J. Mi, W. Ji, and X. H. Zhang

Appl. Phys. Lett. 88, 061107 (2006); http://dx.doi.org/10.1063/1.2172161 (3 pages) | Cited 22 times

Online Publication Date: 7 February 2006

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Optically pumped lasing with low threshold and narrow linewidth was observed in a 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran dye-doped holographic polymer-dispersed liquid crystal transmission grating structure. The results showed that the lasing peak centered at about 609 nm, with a full width at half maximum of about only 1.8 nm. The threshold pumping intensity was about 120 μJ under the excitation of a frequency-doubled Nd:yttrium–aluminum–garnet laser operating at a wavelength of 532 nm. Theoretical calculation showed that the lasing from this structure happened at the band edge of the photonic band gap. The lasing modes were also investigated. The transmission grating investigated enjoys a much larger gain length compared to the reflection one.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.40.Eq Holographic optical elements; holographic gratings

Semiconductor-laser-pumped high-power upconversion laser

Ernst Heumann, Sebastian Bär, Katja Rademaker, Günter Huber, Stuart Butterworth, Andreas Diening, and Wolf Seelert

Appl. Phys. Lett. 88, 061108 (2006); http://dx.doi.org/10.1063/1.2172293 (3 pages) | Cited 31 times

Online Publication Date: 7 February 2006

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A high-power optically pumped semiconductor laser operating around 970 nm has been used as a pumping source for an upconversion laser based on an Er3+ doped LiLuF4 crystal. Nearly 0.5 W of continuous wave (cw) output power and 0.8 W peak power at a 50% pump duty cycle could be achieved at a wavelength of 552 nm. This represents the highest output power from a room temperature upconversion laser ever reported. Laser threshold and slope efficiency were measured to be below 100 mW of absorbed pump power and 30%, respectively. This experiment could be an important step along the route to realizing a compact and efficient upconversion laser emitting in the Watt level power regime.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Simultaneous time and frequency gating of weak molecular fluorescence in a thick nonlinear crystal

M. P. A. Branderhorst, P. Wasylczyk, and I. A. Walmsley

Appl. Phys. Lett. 88, 061109 (2006); http://dx.doi.org/10.1063/1.2172297 (3 pages) | Cited 4 times

Online Publication Date: 7 February 2006

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Time and frequency gating of molecular spontaneous emission at a less than one photon per mode level is achieved using phase matching properties of sum frequency generation in a 3 mm type I BBO crystal. The results of time and frequency resolved fluorescence measurements from a vibrational wavepacket in diatomic potassium molecules are presented. The experimental arrangement is simplified compared to the classical setup which uses a short crystal and monochromator. Both the signal and the signal to noise ratio increase.
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33.50.Dq Fluorescence and phosphorescence spectra
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
33.15.Mt Rotation, vibration, and vibration-rotation constants

Directed vertical alignment liquid crystal display with fast switching

Mingxia Gu, Ivan I. Smalyukh, and Oleg D. Lavrentovich

Appl. Phys. Lett. 88, 061110 (2006); http://dx.doi.org/10.1063/1.2172299 (3 pages) | Cited 10 times

Online Publication Date: 7 February 2006

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We describe a directed vertical alignment (VA) display mode based on a nematic liquid crystal (LC) doped with a chiral dopant and confined between two substrates, one of which is pretreated, say, by unidirectional rubbing or photoalignment. The design allows one to eliminate umbilical defects that appear during switching of the conventional VA cells and thus to obtain better contrast. Switching is ∼ 30% faster than for VA cells when optimized concentration of a chiral dopant is added and LC molecules at one of the substrates are slightly tilted from the cell normal due to the unidirectional surface treatment.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
81.65.-b Surface treatments

Realtime study of plume ejection dynamics in silicon laser ablation under 5 ns pulses

Jun Ren, Xiaobo Yin, Sergei S. Orlov, and Lambertus Hesselink

Appl. Phys. Lett. 88, 061111 (2006); http://dx.doi.org/10.1063/1.2172406 (3 pages) | Cited 2 times

Online Publication Date: 8 February 2006

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We present results of nanosecond laser ablation of silicon over a broad range of laser intensities, investigated by studying the time evolution of the ablation plume ejection, which, as measured by transmission of a probe beam, consists of a fast ejection phase followed by a delayed slow ejection phase. Experimental results indicate that different physical processes dominate at different ablation stages. The laser intensity threshold for the appearance of the slow ejection is ∼ 30 GW/cm2. The plume kinetics parameters extracted from our experiments agree well with estimations based on blast wave and homogeneous nucleation theories, providing a physical explanation for the observed ablation rate dependence on the laser light intensity.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Optical waveguiding using thermal gradients across homogeneous liquids in microfluidic channels

Sindy K. Y. Tang, Brian T. Mayers, Dmitri V. Vezenov, and George M. Whitesides

Appl. Phys. Lett. 88, 061112 (2006); http://dx.doi.org/10.1063/1.2170435 (3 pages) | Cited 22 times

Online Publication Date: 8 February 2006

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This letter describes the design and operation of a liquid-core liquid-cladding (L2) optical waveguide composed of a thermal gradient across a compositionally homogeneous liquid flowing in a microfluidic channel at low Reynolds number. Two streams of liquid at a higher temperature (the cladding) sandwich a stream of liquid at a lower temperature (the core). This temperature difference results in a contrast in refractive index across the width of the channel that is sufficient to guide light. The use of a single homogeneous liquid in this L2 system simplifies recycling, and facilitates closed-loop operation. Furthermore, with radiative and inline heating of the liquids, it should be possible to reconfigure this optical system with considerable flexibility.
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42.79.Gn Optical waveguides and couplers
42.15.Eq Optical system design
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet

Tae-In Jeon and D. Grischkowsky

Appl. Phys. Lett. 88, 061113 (2006); http://dx.doi.org/10.1063/1.2171488 (3 pages) | Cited 45 times

Online Publication Date: 8 February 2006

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We present an experimental study of the propagation of the THz Zenneck surface wave on an aluminum sheet, now more commonly denoted as the THz surface plasmon (TSP). Here, the TSP pulse is generated by coupling the THz pulse from a metal parallel-plate waveguide onto the aluminum sheet; the propagated TSP pulse is detected at the output end of the sheet using a standard photoconductive dipole antenna. We separate the associated free-space THz pulse from the TSP pulse using a curved sheet. The observed weakly guided TSP propagation has the expected low group velocity dispersion, but also has anomalously high attenuation and much tighter binding to the metal surface than predicted by Zenneck theory.
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78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Gn Optical waveguides and couplers

High-resolution spectral hole burning in InGaAs-GaAs quantum dots

J. J. Berry, Martin J. Stevens, R. P. Mirin, and K. L. Silverman

Appl. Phys. Lett. 88, 061114 (2006); http://dx.doi.org/10.1063/1.2172291 (3 pages) | Cited 6 times

Online Publication Date: 8 February 2006

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We report the use of continuous wave spectral hole burning to perform high-resolution spectroscopy of the homogeneous linewidth of self-assembled InGaAs-GaAs quantum dots at low temperature. We use this technique to examine the power broadening behavior of the homogeneous InGaAs-GaAs quantum dot line. We find that at a temperature of 9.8 K and over the majority of the pump powers considered, the spectral hole signal is well fit by a single Lorentizian line shape. Analysis of the power broadening yields a full width at half maximum of 0.74 μeV for the homogeneous linewidth and a corresponding coherence time T2 of 1.76 ns.
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78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.-k Nonlinear optics

Effect of the lossy layer thickness of metal cylindrical waveguide wall on the propagation constant of electromagnetic modes

Jirun Luo and Chongqing Jiao

Appl. Phys. Lett. 88, 061115 (2006); http://dx.doi.org/10.1063/1.2172735 (3 pages) | Cited 4 times

Online Publication Date: 9 February 2006

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Based on the dispersion equation of electromagnetic mode, the propagation problem in a lossy cylindrical waveguide is studied. The analytic formula of propagation constant for any mode in the waveguide is presented, which includes the effect of the lossy layer thickness on the waveguide wall. The analysis with the analytic formula shows that the lossy layer thickness has great effect on the propagation constant when the thickness is 1.5 times smaller than the skin depth of good conductor (δ).
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84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings

B. M. Holmes and D. C. Hutchings

Appl. Phys. Lett. 88, 061116 (2006); http://dx.doi.org/10.1063/1.2172648 (3 pages) | Cited 7 times

Online Publication Date: 9 February 2006

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The demonstration of quasi-phase-matched nonreciprocal polarization rotation in a waveguide comprising a conventional III-V semiconductor core and lower cladding is reported. The approach, which is achieved through the incorporation of a periodic upper cladding that alternates between magneto-optic and nonmagneto-optic media, overcomes many of the problems traditionally encountered when transferring the principles of free-space Faraday-effect optical isolators into waveguide geometries. An enhancement of polarization rotation many times greater than that achievable in the absence of phase matching is observed. Additionally, the technique facilitates an ability to select and/or manipulate individual modes from multimode waveguides.
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42.82.Et Waveguides, couplers, and arrays
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.79.Wc Optical coatings

Sharp waveguide bends induced by spatial solitons

Robert Jäger, Simon-Pierre Gorza, Cyril Cambournac, Marc Haelterman, and Mathieu Chauvet

Appl. Phys. Lett. 88, 061117 (2006); http://dx.doi.org/10.1063/1.2172649 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2006

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We experimentally demonstrate the ability of a self-guided laser beam to induce waveguides with sharp bends. The beam is a two-dimensional photorefractive screening-photovoltaic bright spatial soliton generated inside a biased lithium-niobate crystal shaped as a prism. The soliton robustness against total internal reflections is shown to leave place to a low-loss unimodal waveguide undergoing multiple zero-radius 90° turns.
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42.65.Tg Optical solitons; nonlinear guided waves
42.65.Wi Nonlinear waveguides
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Observation of optical instabilities in the photoluminescence of InGaN single quantum well

Ruggero Micheletto, Masayoshi Abiko, Akio Kaneta, Yoichi Kawakami, Yukio Narukawa, and Takashi Mukai

Appl. Phys. Lett. 88, 061118 (2006); http://dx.doi.org/10.1063/1.2172144 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2006

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We investigate a peculiar optical instability (blinking) phenomena associated with spatial inhomogeneity in InxGa(1−x)N single quantum well systems. We studied the time dependence of this dynamic phenomenon and tested a “quantum jump” single exponential model on the system. A comparative analysis of the behavior of different samples suggests that indium-rich localized centers participate in the mechanism of blinking and that the instability behavior differs with the excitation wavelength. Our study indicates that the trapping and de-trapping process between the localized-luminescent centers and surrounding less luminous regions plays important roles in the carrier recombination mechanism.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.63.Hs Quantum wells
73.21.Fg Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Monte Carlo simulation of hot phonon effects in resonant-phonon-assisted terahertz quantum-cascade lasers

J. T. Lü and J. C. Cao

Appl. Phys. Lett. 88, 061119 (2006); http://dx.doi.org/10.1063/1.2172225 (3 pages) | Cited 29 times

Online Publication Date: 9 February 2006

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We study the influence of nonequilibrium optical phonons on the electron transport in resonant-phonon-assisted terahertz (THz) quantum-cascade lasers (QCLs). The hot phonon effect is included in the Monte Carlo simulation by introducing a time constant accounting for the decay of polar optical phonons into other phonon modes. We find that nonequilibrium polar optical phonons may modify the electron-phonon interaction, affect the electron distribution in different subbands, and consequently change the device current. We conclude that the hot phonon effect should be taken into account in the study of the transport properties of resonant-phonon-assisted THz QCLs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
02.50.Ng Distribution theory and Monte Carlo studies

Use of a long-duration ns pulse for efficient emission of spectral lines from the laser ablation plume in water

Tetsuo Sakka, Hisayuki Oguchi, Satoru Masai, Kohichi Hirata, Yukio H. Ogata, Morihisa Saeki, and Hironori Ohba

Appl. Phys. Lett. 88, 061120 (2006); http://dx.doi.org/10.1063/1.2172235 (3 pages) | Cited 13 times

Online Publication Date: 9 February 2006

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The effect of pulse duration upon the line profile of Cu I emission observed by laser ablation of a copper metal plate immersed in water has been examined. By irradiating a pulse with the duration longer than 40 ns the spectral profile with clear narrow emission lines of Cu atoms is obtained, while the emission spectra always suffer from broadening and self-absorption by the irradiation of the 20 ns pulse for the ablation. The results show that the use of a long-duration pulse enables in situ elemental analysis of the solid surface in contact with a bulk liquid.
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79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
81.05.Bx Metals, semimetals, and alloys
81.65.-b Surface treatments

One quarter million (500×500) pixel arrays of silicon microcavity plasma devices: Luminous efficacy above 6 lumens/watt with Ne/50% Xe mixtures and a green phosphor

K.-F. Chen, N. P. Ostrom, S.-J. Park, and J. G. Eden

Appl. Phys. Lett. 88, 061121 (2006); http://dx.doi.org/10.1063/1.2171794 (3 pages) | Cited 11 times

Online Publication Date: 10 February 2006

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Arrays comprising 250 000 Si microcavity plasma devices, each with an emitting aperture of 50×50 μm2 and tapered sidewalls (inverted pyramid cavity), have been fabricated in 100-mm (4″) diam. wafers and operated in the rare gases and Ar/N2 mixtures with sinusoidal ac or bipolar dc excitation. Having an overall active area of 25 cm2 and a 25% filling factor, these 500×500 arrays exhibit the pixel-to-pixel emission uniformity characteristics of arrays at least a factor of 6 smaller, and yet are efficient in generating vacuum ultraviolet (VUV) radiation. Luminous efficacies above 6 lm/W and luminance values approaching 2000 cd/m2 are measured when a 500×500 array, operating with a Ne/50% Xe gas mixture, illuminates a 20-μm-thick film of a commercial green phosphor (Mn:Zn2SiO4). Despite the nonoptimal transmission geometry of the array-phosphor structure, the efficacy and luminance produced by the VUV-driven phosphor for a Ne/50% Xe mixture and a total pressure of 800 Torr are measured to be 7.2±0.6 lm/Watt and 525±75 cd/m2, respectively, for a 20-kHz sinusoidal ac voltage of ∼ 284 V rms. Maximizing the luminous efficacy–luminance product lowers the optimal pressure of Ne/50% Xe mixtures to roughly 1 atm. The magnitude of the radiant output generated by these arrays, in addition to the rapid rise in emitting efficiency with increased Xe content in Ne/10%–50% Xe mixtures, suggest that this microplasma array structure will be of value for both microdisplay and biomedical applications.
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85.60.Pg Display systems
52.75.-d Plasma devices
42.82.Gw Other integrated-optical elements and systems
85.30.-z Semiconductor devices

Electrically controllable laser based on cholesteric liquid crystal with negative dielectric anisotropy

Tsung-Hsien Lin, Hung-Chang Jau, Ching-Hsu Chen, Yi-Jan Chen, Tai-Huei Wei, Chen-Wei Chen, and Andy Y.-G. Fuh

Appl. Phys. Lett. 88, 061122 (2006); http://dx.doi.org/10.1063/1.2168259 (3 pages) | Cited 23 times

Online Publication Date: 10 February 2006

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This work examines a planar cholesteric liquid crystal (CLC) cell with a negative dielectric anisotropy, doped with laser dye, as an electrically tunable one-dimensional photonic crystal laser device. The lasing wavelength is demonstrated to be tunable by applying a voltage. Additionally, lasing can be switched on and off changing the frequency of the applied voltage. Wavelength tuning caused by the shift of the reflection band of CLC is attributed to the electrohydrodynamical effect in the negative dielectric cell.
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42.55.Mv Dye lasers
42.55.Tv Photonic crystal lasers and coherent effects
42.79.Kr Display devices, liquid-crystal devices
42.60.Fc Modulation, tuning, and mode locking

Polarization-independent and fast-response phase modulators using double-layered liquid crystal gels

Hongwen Ren, Yi-Hsin Lin, and Shin-Tson Wu

Appl. Phys. Lett. 88, 061123 (2006); http://dx.doi.org/10.1063/1.2173248 (3 pages) | Cited 10 times

Online Publication Date: 10 February 2006

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A polarization-independent phase modulator using two thin homogeneously stratified but orthogonally oriented liquid crystal (LC) gels is demonstrated. In addition to polarization independence and submillisecond response time, the LC gel possesses a much larger phase change and lower operating voltage than the nanosized polymer-dispersed liquid crystal. For a 16 μm transmissive E48 LC gel, the phase shift exceeds 1π at λ = 633 nm with an electric field strength of ∼ 11 Vrms/μm. Potential applications of such a phase modulator for laser beam steering, microlens array, and switchable two- and three-dimensional LC displays are foreseeable.
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42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution

Aurélien David, Tetsuo Fujii, Rajat Sharma, Kelly McGroddy, Shuji Nakamura, Steven P. DenBaars, Evelyn L. Hu, Claude Weisbuch, and Henri Benisty

Appl. Phys. Lett. 88, 061124 (2006); http://dx.doi.org/10.1063/1.2171475 (3 pages) | Cited 84 times

Online Publication Date: 10 February 2006

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We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.
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42.70.Qs Photonic bandgap materials
85.60.Jb Light-emitting devices
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