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24 Oct 2005

Volume 87, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages)

T. Kimura, Y. Otani, and J. Hamrle
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Efficiency limits of photovoltaic fluorescent collectors

Uwe Rau, Florian Einsele, and Gerda C. Glaeser

Appl. Phys. Lett. 87, 171101 (2005); http://dx.doi.org/10.1063/1.2112196 (3 pages) | Cited 30 times

Online Publication Date: 17 October 2005

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This paper examines the thermodynamic limits of photovoltaic solar energy conversion by fluorescent collectors. The maximum efficiency of a fluorescent collector corresponds to the Shockley–Queisser limit for a nonconcentrating solar cell with a single bandgap energy. To achieve this efficiency, the collector requires a photonic structure at its surface that acts as an omnidirectional spectral band stop filter. The large potential of photonic structures for the efficiency enhancement of idealized as well as real fluorescent collectors is highlighted.
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42.79.Ek Solar collectors and concentrators
84.60.Jt Photoelectric conversion
42.79.Ci Filters, zone plates, and polarizers

Ultraslow light (<200 m/s) propagation in a semiconductor nanostructure

Phedon Palinginis, Shanna Crankshaw, Forrest Sedgwick, Eui-Tae Kim, Michael Moewe, Connie J. Chang-Hasnain, Hailin Wang, and Shun-Lien Chuang

Appl. Phys. Lett. 87, 171102 (2005); http://dx.doi.org/10.1063/1.2112197 (3 pages) | Cited 27 times

Online Publication Date: 17 October 2005

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We report time-domain measurements of ultraslow light propagation in a semiconductor quantum-well structure using coherent population oscillation. Delays greater than 1 ns are achieved for an amplitude-modulated optical beam propagating through a 195-nm-long active region, corresponding to group velocities less than 200 m/s. Delays can be easily varied by adjusting the intensity of the control laser. The bandwidth is suitable to delay sub-GHz modulated optical signals.
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78.67.De Quantum wells
42.65.-k Nonlinear optics

Self-fabrication of void array in fused silica by femtosecond laser processing

Eiji Toratani, Masanao Kamata, and Minoru Obara

Appl. Phys. Lett. 87, 171103 (2005); http://dx.doi.org/10.1063/1.2115097 (3 pages) | Cited 19 times

Online Publication Date: 18 October 2005

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We demonstrate self-fabrication of a submicrometer-sized void array in fused silica using a 100 fs 0.2–3 μJ Ti:Sapphire femtosecond laser and a high 0.9 numerical aperture (NA) objective lens. The effect of the focusing conditions of NA, laser energy, and pulse number on the shape of the fabricated void was investigated. The void has a linearly drawn shape in the direction of the laser irradiation when a single pulse is irradiated and an increasing number of incident pulses resulted in the break up of the long void into multiple spherical ones, leading to a periodically aligned void array. The void shape also varied with the depth of the focus point beneath the fused silica surface, because the amount of self-focusing has a significant effect on the generation of the voids. The void shape was narrower and longer when the laser pulse was focused with the higher NA (up to 0.9) objective lens in the deeper position (up to 70 μm) in the fused silica.
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42.86.+b Optical workshop techniques
42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Adiabatic matching stage for coupling of light to extended Bloch modes of photonic crystals

B. Momeni and A. Adibi

Appl. Phys. Lett. 87, 171104 (2005); http://dx.doi.org/10.1063/1.2115081 (3 pages) | Cited 34 times

Online Publication Date: 19 October 2005

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In this letter, we present a matching stage for reflection reduction based on the principle of gradual change to efficiently couple light to propagating modes of photonic crystals (PCs). Basic physical considerations in designing these matching stages are investigated and a systematic yet simple design procedure is suggested. We show that matching stages obtained using this method are wideband in frequency, have a wide acceptance angle, and are robust against fabrication imperfections. Therefore, they are the preferred choice in general-purpose matching stages to be used along with dispersion-based PC devices.
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42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

High-performance photorefractive polymer operating at 1550 nm with near-video-rate response time

Savaş Tay, Jayan Thomas, Muhsin Eralp, Guoqiang Li, Robert A. Norwood, Axel Schülzgen, Michiharu Yamamoto, Stephen Barlow, Gregory A. Walker, Seth R. Marder, and N. Peyghambarian

Appl. Phys. Lett. 87, 171105 (2005); http://dx.doi.org/10.1063/1.2117610 (3 pages) | Cited 6 times

Online Publication Date: 20 October 2005

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The development of a high-performance photorefractive polymer composite operating at 1550 nm is reported. We show 40% internal diffraction efficiency with response time of 35 ms and a net gain of 20 cm−1 in four-wave mixing and two-beam coupling experiments, respectively. This is more than an order of magnitude improvement in the diffraction efficiency and net two beam coupling gain and two orders of magnitude in the response time than the previously reported photorefractive polymer operating at this technologically important wavelength. The improvement in photorefractive characteristics is accomplished by an enhanced orientation of the nonlinear optical chromophore in the present composite.
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42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics

Experimental demonstration of Fano-type resonance in photoluminescence of ZnS:Mn/SiO2 one-dimensional photonic crystals

Takeshi Baba, Hisao Makino, Takahiro Mori, Takashi Hanada, Takafumi Yao, and Hyun-Yong Lee

Appl. Phys. Lett. 87, 171106 (2005); http://dx.doi.org/10.1063/1.2117611 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2005

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We investigated the photoluminescence (PL) properties of ZnS:Mn/SiO2 one-dimensional photonic-crystal structures. PL spectra were measured from two opposite directions perpendicular to the sample. The cavity mode emission measured from the sample surface showed asymmetric spectral shape; measurements from the back side of the sample showed a symmetric spectral shape. The experimental spectra were analyzed by a simple model calculation based on the transfer matrix method. From the model calculation, it was found that the asymmetric shape observed in cavity mode emission is caused by Fano-type resonance which is the coupling effect between discrete emission from the ZnS:Mn cavity layer and continuous background emission from all ZnS:Mn layers except the cavity layer.
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78.55.Hx Other solid inorganic materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
42.70.Qs Photonic bandgap materials

III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy

Gon Namkoong, Kyoung-Keun Lee, Shannon M. Madison, Walter Henderson, Stephen E. Ralph, and W. Alan Doolittle

Appl. Phys. Lett. 87, 171107 (2005); http://dx.doi.org/10.1063/1.2084340 (3 pages) | Cited 17 times

Online Publication Date: 21 October 2005

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Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000 °C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN/GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Second-harmonic performance of a-axis-oriented ZnO nanolayers on sapphire substrates

Uwe Neumann, Ruediger Grunwald, Uwe Griebner, Günter Steinmeyer, Martin Schmidbauer, and Wolfgang Seeber

Appl. Phys. Lett. 87, 171108 (2005); http://dx.doi.org/10.1063/1.2112199 (3 pages) | Cited 12 times

Online Publication Date: 21 October 2005

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We report on the nonlinear optical performance of sub-μm ZnO films grown by metal organic aerosol deposition on r-plane sapphire substrates. These films display scale-like nanocrystalline structures. Layers of different crystallite sizes and shapes are studied. Both, x-ray diffractometry and the characteristic angular and polarization dependence of the second harmonic generation, indicate a strongly uniform a-axis orientation of the crystallites. Using 35-fs Ti:sapphire laser pulses, we demonstrate much higher conversion efficiencies for ZnO layers than previously reported. The robust performance at normal incidence makes this device suitable for advanced pulse characterization techniques.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Nv Optical frequency converters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Hf II-VI semiconductors
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.47.-p Spectroscopy of solid state dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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