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1 Nov 2007

Volume 102, Issue 9, Articles (09xxxx)

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J. Appl. Phys. 102, 091101 (2007); http://dx.doi.org/10.1063/1.2804122 (21 pages)

Franky So, Benjamin Krummacher, Mathew K. Mathai, Dmitry Poplavskyy, Stelios A. Choulis, and Vi-En Choong
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Effects of shapes and orientations of reversed domains on the conversion efficiency of second harmonic wave in two-dimensional nonlinear photonic crystals

Jingjuan Li, Zhiyuan Li, and Daozhong Zhang

J. Appl. Phys. 102, 093101 (2007); http://dx.doi.org/10.1063/1.2803740 (5 pages) | Cited 1 time

Online Publication Date: 2 November 2007

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The conversion efficiency of second harmonic wave in two-dimensional nonlinear photonic crystals consisting of square lattice and reversed domains of various shapes and orientations is studied numerically. Different shapes of reversed domains (circle, ellipse, rectangle, and square) are considered. We present numerical results and theoretical validations. The results indicate that for a given lattice symmetry and a fixed filling factor, the conversion efficiency of different order quasiphase matched process can be maximized by adjusting the shape and orientation of the reversed domains.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals

High resolution selective multilayer laser processing by nanosecond laser ablation of metal nanoparticle films

Seung H. Ko, Heng Pan, David J. Hwang, Jaewon Chung, Sangil Ryu, Costas P. Grigoropoulos, and Dimos Poulikakos

J. Appl. Phys. 102, 093102 (2007); http://dx.doi.org/10.1063/1.2802302 (9 pages) | Cited 10 times

Online Publication Date: 5 November 2007

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Ablation of gold nanoparticle films on polymer was explored using a nanosecond pulsed laser, with the goal to achieve feature size reduction and functionality not amenable with inkjet printing. The ablation threshold fluence for the unsintered nanoparticle deposit was at least ten times lower than the reported threshold for the bulk film. This could be explained by the combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and the relatively weak bonding between nanoparticles. The ablation physics were verified by the nanoparticle sintering characterization, ablation threshold measurement, time resolved ablation plume shadowgraphs, analysis of ablation ejecta, and the measurement and calculation of optical properties. High resolution and clean feature fabrication with small energy and selective multilayer processing are demonstrated.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.16.Mk Laser-assisted deposition
42.62.-b Laser applications
81.65.-b Surface treatments
78.66.Bz Metals and metallic alloys

Design of n-type silicon-based quantum cascade lasers for terahertz light emission

Kristina Driscoll and Roberto Paiella

J. Appl. Phys. 102, 093103 (2007); http://dx.doi.org/10.1063/1.2803896 (8 pages) | Cited 5 times

Online Publication Date: 6 November 2007

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The design of terahertz quantum cascade lasers based on electronic intersubband transitions in Ge/SiGe quantum wells is investigated. A detailed theoretical model of the conduction-band lineup of these heterostructures is first presented and used to show that large quantum confinement in the L valleys can be obtained with properly selected layer compositions and thicknesses. Computation of the key laser design parameters is then discussed, including the important role played by the L-valley ellipsoidal constant-energy surfaces. Finally, the main design issues specific to this material system and its potential for high-performance operation are illustrated by means of two exemplary structures, designed for emission near 50 and 25 μm.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Terahertz gain on shallow donor transitions in silicon

R. Kh. Zhukavin, V. N. Shastin, S. G. Pavlov, H.-W. Hübers, J. N. Hovenier, T. O. Klaassen, and A. F. G. van der Meer

J. Appl. Phys. 102, 093104 (2007); http://dx.doi.org/10.1063/1.2804756 (5 pages) | Cited 4 times

Online Publication Date: 7 November 2007

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Small signal gain measurements of optically excited terahertz silicon lasers are reported. Two types of lasers, Si:P and Si:Bi, were investigated. They were optically excited with radiation from a free electron laser or a CO2 laser. The experiments were performed with an oscillator-amplifier scheme where one sample serves as a laser while the other one is an amplifier. In case of the free electron laser the pump frequency corresponds to intracenter excitation of the 2p0 or 2p± states of the P and Bi Coulomb centers, and the gain was determined for the 2p0→1s(E), 2p0→1s(T2) transitions in Si:P and the 2p±→1s(E) transition in Si:Bi. Pumping with a CO2 laser leads to photoexcitation of the Coulomb centers. In this case the gain was determined for the 2p0→1s(T2) of Si:P transition. The gain for intracenter pumping is in the range 5−10 cm−1 while for photoexcitation the gain is considerably less, namely ∼ 0.5 cm−1. The experimental results are analyzed and found to be in good agreement with theoretical calculations based on balance equations.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.05.Cy Elemental semiconductors

Electro-optical sampling of ultrashort THz pulses by fs-laser pulses at 530 nm with BaTiO3

B. Pradarutti, G. Matthäus, S. Riehemann, G. Notni, J. Limpert, S. Nolte, and A. Tünnermann

J. Appl. Phys. 102, 093105 (2007); http://dx.doi.org/10.1063/1.2809270 (3 pages) | Cited 2 times

Online Publication Date: 14 November 2007

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Electro-optical sampling (EOS) of ultrabroadband terahertz (THz) radiation with the help of ultrashort 530 nm fs-laser pulses is reported. The THz pulses are generated by exciting a surface emitter (InAs) with a parabolic fiber laser amplifier delivering 100 fs pulses at a repetition rate of 75 MHz and an average power of 10 W at 1060 nm. The pulses are frequency doubled to 530 nm for gating and BaTiO3 is used as the detector crystal.
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42.55.Wd Fiber lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Growth and optical properties of KTa1−xNbxO3 thin films grown by pulsed laser deposition on MgO substrates

A. Rousseau, M. Guilloux-Viry, E. Dogheche, M. Bensalah, and D. Remiens

J. Appl. Phys. 102, 093106 (2007); http://dx.doi.org/10.1063/1.2809400 (4 pages) | Cited 6 times

Online Publication Date: 15 November 2007

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Perovskitelike KTa1−xNbxO3 (KTN, x ranging from 0 to 1) thin films were grown on (100)MgO substrates using pulsed laser deposition. X-ray diffraction analyses evidenced the epitaxial growth of the films along the (100) orientation. The optical properties of KTN planar waveguides were characterized by prism coupling for determination of ordinary and extraordinary refractive indices nTE and nTM (transverse electric and transverse magnetic). The influence of Nb content was also investigated relative to the films’ indices. The film behavior and the substrate-to-layer interface were directly qualified from the measured optical data using the experimental and theoretical approach (iWKB) (inverse Wentzel-Kramers-Brillouin). The results showed a change in the refractive index profile at the interface, which may be related to the existence of structural defects.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators

Properties of omnidirectional gap and defect mode of one-dimensional photonic crystal containing indefinite metamaterials with a hyperbolic dispersion

Yuanjiang Xiang, Xiaoyu Dai, Shuangchun Wen, and Dianyuan Fan

J. Appl. Phys. 102, 093107 (2007); http://dx.doi.org/10.1063/1.2809446 (5 pages) | Cited 3 times

Online Publication Date: 15 November 2007

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The structure of one-dimensional photonic crystal (1DPC) containing indefinite metamaterials with a hyperbolic dispersion relation is proposed to realize the omnidirectional gap for the design of omnidirectional reflectors and filters. It is demonstrated that this 1DPC can result in a similar zero average index (zero-math) gap usually appearing in the 1DPC containing isotropic left-handed materials. The properties of zero-math gap and defect modes of this photonic crystal are studied in detail. The edge of this zero-math gap is insensitive to incident angle and polarization of light in contrast to the Bragg gap. When a defect layer is introduced into the 1DPC, a defect mode appears inside the omnidirectional gap. The spectral position of defect mode is found to be weakly dependent on the incident angle of light and nearly invariant to the scale length of photonic crystal.
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42.70.Qs Photonic bandgap materials
61.72.-y Defects and impurities in crystals; microstructure

Dynamic control of visible radiation by a liquid crystal filled Fabry-Pérot etalon

S. A. Jewell, S. L. Cornford, and J. R. Sambles

J. Appl. Phys. 102, 093108 (2007); http://dx.doi.org/10.1063/1.2809448 (4 pages)

Online Publication Date: 15 November 2007

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A liquid crystal filled Fabry-Pérot etalon has been constructed to control the resonant transmission of electromagnetic radiation over the visible range of the spectrum. This has been achieved through the use of a 1.5 μm thick homogeneously aligned liquid crystal layer in the core of a silver-clad etalon structure. Applying an electric field across the core reorientates the liquid crystal director and changes the refractive index for incident light polarized parallel to the rubbing direction. By measuring the transmitted intensity as a function of wavelength for a variety of applied voltages shifts in the positions of the resonant transmission modes of up to 80 nm have been observed. In addition, these results have been compared to model data generated using a multilayer optics model to obtain the dispersion of the liquid crystal over the visible range of the electromagnetic spectrum.
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07.60.Ly Interferometers
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.40.Dw Liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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