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15 Feb 2010

Volume 107, Issue 4, Articles (04xxxx)

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J. Appl. Phys. 107, 041101 (2010); http://dx.doi.org/10.1063/1.3318287 (13 pages)

Y. C. Tao and J. G. Hu
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back to top Lasers, Optics, and Optoelectronics

Comparison of the performance of photonic band-edge liquid crystal lasers using different dyes as the gain medium

Carrie Mowatt, Stephen M. Morris, Myoung Hoon Song, Timothy D. Wilkinson, Richard H. Friend, and Harry J. Coles

J. Appl. Phys. 107, 043101 (2010); http://dx.doi.org/10.1063/1.3284939 (9 pages) | Cited 14 times

Online Publication Date: 16 February 2010

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The primary concern of this work is to study the emission characteristics of a series of chiral nematic liquid crystal lasers doped with different laser dyes (DCM, pyrromethene 580, and pyrromethene 597) at varying concentrations by weight (0.5–2 wt %) when optically pumped at 532 nm. Long-wavelength photonic band-edge laser emission is characterized in terms of threshold energy and slope efficiency. At every dye concentration investigated, the pyrromethene 597-doped lasers exhibit the highest slope efficiency (ranging from 15% to 32%) and the DCM-doped lasers the lowest (ranging from 5% to 13%). Similarly, the threshold was found to be, in general, higher for the DCM-doped laser samples in comparison to the pyrromethene-doped laser samples. These results are then compared with the spectral properties, quantum efficiencies and, where possible, fluorescence lifetimes of the dyes dispersed in a common nematic host. In accordance with the low thresholds and high slope efficiencies, the results show that the molar extinction coefficients and quantum efficiencies are considerably larger for the pyrromethene dyes in comparison to DCM, when dispersed in the liquid crystal host.
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42.55.Mv Dye lasers
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Hj Laser materials

Generation of a dynamic polarized laser beam for applications in laser welding

Stephan Gräf, Gisbert Staupendahl, Carlo Seiser, Bernd-Jürgen Meyer, and Frank A. Müller

J. Appl. Phys. 107, 043102 (2010); http://dx.doi.org/10.1063/1.3295911 (6 pages) | Cited 1 time

Online Publication Date: 18 February 2010

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The temporal control and optimization of laser beam parameters, e.g., the beam power, can be employed to enhance the quality and reliability of the welding process. Until now, the influence of a time-dependent beam polarization has been less investigated in welding. The publication describes a new experimental arrangement allowing the fast variation of the polarization of CO2 laser radiation [“dynamic polarization” (DP)]. The key element of the setup is a high power interference laser beam modulator for cw laser power rating of up to 4 kW. Weld seams were produced with different process parameters in the technically relevant steels St37 and Ck45 and in the precoated steel 22MnB5 (USIBOR 1500P). The welds were subsequently characterized by roughness measurements of the top bead surfaces and by the preparation of cross sections and their macroscopic analysis. The experiments on welding with DP showed a significant influence on the keyhole and melt pool dynamics, especially a reduction in the top bead roughness at certain DP frequencies up to a factor of about 3. In addition, a threshold behavior for this effect was observed. It was shown that the cross sectional shape and thus the degree of energy coupling to the material was unaffected by the DP. Finally, during welding USIBOR 1500P with DP an enhanced melt pool stirring was achieved. The results show that the temporal modulation of energy coupling to the material caused by DP is suitable to enhance the quality and reliability of the welding process.
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42.62.Cf Industrial applications

Highly efficient blue organic light emitting device using indium-free transparent anode Ga:ZnO with scalability for large area coating

Liang Wang, Dean W. Matson, Evgueni Polikarpov, James S. Swensen, Charles C. Bonham, Lelia Cosimbescu, Joseph J. Berry, David S. Ginley, Daniel J. Gaspar, and Asanga B. Padmaperuma

J. Appl. Phys. 107, 043103 (2010); http://dx.doi.org/10.1063/1.3282526 (8 pages) | Cited 7 times

Online Publication Date: 19 February 2010

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Organic light emitting devices have been achieved with an indium-free transparent anode, Ga doped ZnO (GZO). A large area coating technique was used (RF magnetron sputtering) to deposit the GZO films onto glass. The respective organic light emitting devices exhibited an operational voltage of 3.7 V, an external quantum efficiency of 17%, and a power efficiency of 39 lm/W at a current density of 1 mA/cm2. These parameters are well within acceptable standards for blue OLEDs to generate a white light with high enough brightness for general lighting applications. It is expected that high-efficiency, long-lifetime, large area, and cost-effective white OLEDs can be made with these indium-free anode materials.
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85.60.Jb Light-emitting devices
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering

Shape measurement of objects using an ultrafast optical Kerr gate of bismuth glass

Wenjiang Tan (谭文疆), Yi Yang (杨毅), Jinhai Si (司金海), Junyi Tong (佟俊仪), Wenhui Yi (易文辉), Feng Chen (陈烽), and Xun Hou (侯洵)

J. Appl. Phys. 107, 043104 (2010); http://dx.doi.org/10.1063/1.3310492 (3 pages) | Cited 4 times

Online Publication Date: 22 February 2010

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An ultrafast optical Kerr gate of Bi2O3–B2O3–SiO2 oxide glass (BI glass) was used in an ultrafast time-resolved imaging system for shape measurement of objects. The experimental results showed that the longitudinal resolution of the imaging system using the ultrafast optical Kerr gate was less than 20 μm and the measurements of object shape using the ultrafast optical Kerr gate of BI glass had more advantages compared with that using CS2.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.-e Optical elements, devices, and systems
06.60.Jn High-speed techniques (microsecond to femtosecond)

Increasing the coupling efficiency of a microdisk laser to waveguides by using well designed spiral structures

Danyu Liu, Haroldo T. Hattori, Lan Fu, Hark Hoe. Tan, and Chennupati Jagadish

J. Appl. Phys. 107, 043105 (2010); http://dx.doi.org/10.1063/1.3309748 (8 pages) | Cited 1 time

Online Publication Date: 23 February 2010

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In this article, we optimize the coupling efficiency from a GaAs microdisk resonator into a single mode spiral waveguide. A classical microdisk resonator coupling light into a nonevanescent straight waveguide reaches a typical coupling efficiency of 67%. We show that the introduction of a spiral waveguide that works both as a waveguide and circular Bragg reflector can improve such efficiency to almost 90%. The same structure with the addition of a taper can couple up to 80% of the generated power into a slot waveguide.
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42.55.Sa Microcavity and microdisk lasers

Interaction of a high-power laser beam with metal sheets

C. D. Boley, K. P. Cutter, S. N. Fochs, P. H. Pax, M. D. Rotter, A. M. Rubenchik, and R. M. Yamamoto

J. Appl. Phys. 107, 043106 (2010); http://dx.doi.org/10.1063/1.3284204 (5 pages) | Cited 4 times

Online Publication Date: 24 February 2010

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Experiments with a high-power laser beam directed onto thin aluminum sheets, with a large spot size, demonstrate that airflow produces a strong enhancement of the interaction. The enhancement is explained in terms of aerodynamic effects. As laser heating softens the material, the airflow-induced pressure difference between front and rear faces causes the metal to bulge into the beam. The resulting shear stresses rupture the material and remove it at temperatures well below the melting point. The material heating is shown to conform to an elementary model. We present an analytic model of elastic bulging. Scaling with respect to spot size, wind speed, and material parameters is determined.
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79.20.Ds Laser-beam impact phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.dj Melting of specific substances

Near infrared quantum cutting in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 transparent ceramics for crystalline silicon solar cells

Hui Lin, Shengming Zhou, Hao Teng, Yukun Li, Wenjie Li, Xiaorui Hou, and Tingting Jia

J. Appl. Phys. 107, 043107 (2010); http://dx.doi.org/10.1063/1.3298907 (4 pages) | Cited 11 times

Online Publication Date: 25 February 2010

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Near infrared (NIR) quantum cutting involving the conversion of an absorbed blue photon into two NIR photons emission has been realized in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 (x = 0.1, 0.25, and 0.5) transparent ceramics. Upon the 467 nm excitation, the energy transfer process was dominated by the cooperative downconversion from the 5d1 state of one Ce3+ ion to the math5/2 state of two Yb3+ ions. The influence of the Ce4+–Yb2+ charge transfer state (CTS) should not contribute much to the energy transfer process for the large energy gap between Ce3+:5d1 and the CTS. The calculated quantum yield of Yb3+ for the x = 0.25 sample without concentration quenching was 175.4%.
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88.40.H- Solar cells (photovoltaics)
71.20.Mq Elemental semiconductors
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Highly nonlinear tellurite microstructured fibers for broadband wavelength conversion and flattened supercontinuum generation

Guanshi Qin, Xin Yan, Chihiro Kito, Meisong Liao, Takenobu Suzuki, Atsushi Mori, and Yasutake Ohishi

J. Appl. Phys. 107, 043108 (2010); http://dx.doi.org/10.1063/1.3311566 (4 pages) | Cited 2 times

Online Publication Date: 25 February 2010

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We demonstrate four-wave mixing-based broadband (>68 nm) wavelength conversion and flattened supercontinuum generation spanning from 900 to 2800 nm in a 36-cm-long tellurite microstructured fiber which has a high nonlinearity. By reducing the size of air holes of the tellurite microstructured fibers, single mode propagation and small dispersion slope are obtained without the propagation loss enhancement. Our results show that chromatic-dispersion controlled tellurite microstructured fibers are promising candidates for nonlinear applications.
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42.81.Bm Fabrication, cladding, and splicing
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.81.Dp Propagation, scattering, and losses; solitons

Rate equations analysis of external-cavity quantum cascade lasers

Q. K. Yang, B. Hinkov, F. Fuchs, W. Bronner, K. Köhler, J. Wagner, R. Maulini, and J. Faist

J. Appl. Phys. 107, 043109 (2010); http://dx.doi.org/10.1063/1.3309764 (7 pages) | Cited 2 times

Online Publication Date: 26 February 2010

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We present a comprehensive analysis of an external-cavity (EC) quantum cascade (QC) laser system, which is based on a coupled-mode system with the length of the EC set equal to that of the laser chip and accommodating the large difference in physical cavity length by introducing an effective speed of light for light propagating in the EC. By analyzing the rate equations and discussing the cross sections and losses of the EC QC lasers, numerical results as well as suggestions for a further optimization of the spectral tuning range of the EC system are presented. Besides, the delayed onset of the EC modes with respect to that of the internal Fabry–Perot modes in pulsed operation has been simulated using the rate equations, yielding a good agreement with the experimental data.
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42.55.Px Semiconductor lasers; laser diodes
42.25.Bs Wave propagation, transmission and absorption
07.60.Ly Interferometers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Superintense fields from multiple ultrashort laser pulses retroreflected in circular geometry

C. H. Raymond Ooi

J. Appl. Phys. 107, 043110 (2010); http://dx.doi.org/10.1063/1.3296128 (5 pages) | Cited 1 time

Online Publication Date: 26 February 2010

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Laser field with superintensity beyond 1029 W/cm2 can be generated by coherent superposition of multiple 100 fs laser pulses in circular geometry setup upon retroreflection by a ring mirror. We have found the criteria for attaining such intensities using broadband ring mirror within the practical damage threshold and paraxial focusing regime. Simple expressions for the intensity enhancement factor are obtained, providing insight for achieving unlimited laser intensity. Higher intensities can be achieved by using few-cycle laser pulses.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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