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22 Jan 2007

Volume 90, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 90, 043507 (2007); http://dx.doi.org/10.1063/1.2435508 (3 pages)

D. Y. Kim and A. J. Steckl
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Manipulating exciton fine structure in quantum dots with a lateral electric field

B. D. Gerardot, S. Seidl, P. A. Dalgarno, R. J. Warburton, D. Granados, J. M. Garcia, K. Kowalik, O. Krebs, K. Karrai, A. Badolato, and P. M. Petroff

Appl. Phys. Lett. 90, 041101 (2007); http://dx.doi.org/10.1063/1.2431758 (3 pages) | Cited 58 times

Online Publication Date: 22 January 2007

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The fine structure of the neutral exciton in a single self-assembled InGaAs quantum dot is investigated under the effect of a lateral electric field. Stark shifts up to 1.5 meV, an increase in linewidth, and a decrease in photoluminescence intensity were observed due to the electric field. The authors show that the lateral electric field strongly affects the exciton fine-structure splitting due to active manipulation of the single particle wave functions. Remarkably, the splitting can be tuned over large values and through zero.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects

Terahertz imaging diagnostics of cancer tissues with a chemometrics technique

Sachiko Nakajima, Hiromichi Hoshina, Masatsugu Yamashita, Chiko Otani, and Norio Miyoshi

Appl. Phys. Lett. 90, 041102 (2007); http://dx.doi.org/10.1063/1.2433035 (3 pages) | Cited 30 times

Online Publication Date: 22 January 2007

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Terahertz spectroscopic images of paraffin-embedded cancer tissues have been measured by a terahertz time domain spectrometer. For the systematic identification of cancer tumors, the principal component analysis and the clustering analysis were applied. In three of the four samples, the cancer tissue was recognized as an aggregate of the data points in the principal component plots. By the agglomerative hierarchical clustering, the data points were well categorized into cancer and the other tissues. This method can be also applied to various kinds of automatic discrimination of plural components by terahertz spectroscopic imaging.
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87.63.-d Non-ionizing radiation equipment and techniques
87.57.N- Image analysis
87.19.X- Diseases
02.50.-r Probability theory, stochastic processes, and statistics

Low transparency current density and high temperature operation from ten-layer p-doped 1.3 μm InAs/InGaAs/GaAs quantum dot lasers

C. Y. Liu, S. F. Yoon, Q. Cao, C. Z. Tong, and H. F. Li

Appl. Phys. Lett. 90, 041103 (2007); http://dx.doi.org/10.1063/1.2434156 (3 pages) | Cited 12 times

Online Publication Date: 22 January 2007

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High temperature photoluminescence up to 100 °C was demonstrated from the p-doped ten-layer InAs/InGaAs quantum dot (QD) laser structure. 1.3 μm InAs QD lasers were fabricated using pulsed anodic oxidation from this structure. High output power of 882 mW and low transparency current density of 5.9 A/cm2/QD layer were obtained. Ground state (GS) lasing could be maintained from a QD laser with short cavity length of 611 μm, corresponding to the maximum modal gain of 23.1 cm−1 from this laser system. GS continuous wave operation up to 100 °C was also demonstrated from an InAs QD laser (50×2500 μm2).
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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

Direct full compensation of the aberrations in quantitative phase microscopy of thin objects by a single digital hologram

L. Miccio, D. Alfieri, S. Grilli, P. Ferraro, A. Finizio, L. De Petrocellis, and S. D. Nicola

Appl. Phys. Lett. 90, 041104 (2007); http://dx.doi.org/10.1063/1.2432287 (3 pages) | Cited 28 times

Online Publication Date: 22 January 2007

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Aberrations and the distortions due to the imaging optics can be compensated in quantitative phase microscopy of thin phase objects by digital holography using a single hologram. The reconstructed quantitative phase microscopy phase distribution map can be directly corrected in the reconstructed image plane by a numerical method. To remove this unwanted aberration, in the special case of thin objects, the authors perform a two-dimensional fit with the Zernike polynomials of the reconstructed unwrapped phase. Subtraction of the fitted polynomial from the original phase map gives quantitative phase microscopy phase map free of aberrations.
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42.40.Kw Holographic interferometry; other holographic techniques
07.60.Pb Conventional optical microscopes
42.30.Wb Image reconstruction; tomography

Phase retrieval in x-ray coherent Fresnel projection-geometry diffraction

Liberato De Caro, Cinzia Giannini, Alessia Cedola, Daniele Pelliccia, Stefano Lagomarsino, and Werner Jark

Appl. Phys. Lett. 90, 041105 (2007); http://dx.doi.org/10.1063/1.2431457 (3 pages) | Cited 4 times

Online Publication Date: 23 January 2007

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Coherent x-ray diffraction experiments were performed in Fresnel regime, within a line-projection geometry. A planar x-ray waveguide was used to focus coherent cylindrical waves onto a 7.2 μm Kevlar fiber, which acts as a phase object for hard x rays. The phase was retrieved, by using a Fourier-based iterative phasing algorithm, consistent with measured diffraction data and known constraints in real space, with a submicrometer spatial resolution.
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61.05.cp X-ray diffraction
07.85.-m X- and γ-ray instruments

Chaos-assisted nonresonant optical pumping of quadrupole-deformed microlasers

Sang-Bum Lee, Juhee Yang, Songky Moon, Jai-Hyung Lee, Kyungwon An, Jeong-Bo Shim, Hai-Woong Lee, and Sang Wook Kim

Appl. Phys. Lett. 90, 041106 (2007); http://dx.doi.org/10.1063/1.2432298 (3 pages) | Cited 9 times

Online Publication Date: 23 January 2007

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Efficient nonresonant optical pumping of a high-Q scar mode in a two-dimensional quadrupole-deformed microlaser has been demonstrated based on ray and wave chaos. Threefold enhancement in the lasing power was achieved at a properly chosen pumping angle. The experimental result is consistent with ray tracing and wave overlap integral calculations.
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42.55.Sa Microcavity and microdisk lasers
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
42.15.Dp Wave fronts and ray tracing

Low dislocation densities and long carrier lifetimes in GaN thin films grown on a SiNx nanonetwork

J. Xie, Ü. Özgür, Y. Fu, X. Ni, H. Morkoç, C. K. Inoki, T. S. Kuan, J. V. Foreman, and H. O. Everitt

Appl. Phys. Lett. 90, 041107 (2007); http://dx.doi.org/10.1063/1.2433754 (3 pages) | Cited 20 times

Online Publication Date: 24 January 2007

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Significant improvement of structural and optical qualities of GaN thin films on sapphire substrates was achieved by metal organic chemical vapor deposition with in situ SiNx nanonetwork. Transmission electron microscope (TEM) studies revealed that screw- and edge-type dislocations were reduced to 4.4×107 and 1.7×107 cm−2, respectively, for a ∼ 5.5-μm-thick layer. Furthermore, room temperature carrier lifetimes of 2.22 and 2.49 ns were measured by time-resolved photoluminescence (TRPL) for samples containing single and double SiNx network layers, respectively, representing a significant improvement over the previous studies. The consistent trends among the TEM, x-ray diffraction, and TRPL measurements suggest that in situ SiNx network reduces line defects effectively as well as the point-defect-related nonradiative centers.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Optical filter based on two-dimensional photonic crystal surface-mode cavity in amorphous silicon-on-silica structure

Ziyang Zhang, Matteo Dainese, Lech Wosinski, Sanshui Xiao, Min Qiu, Marcin Swillo, and Ulf Andersson

Appl. Phys. Lett. 90, 041108 (2007); http://dx.doi.org/10.1063/1.2432228 (3 pages) | Cited 10 times

Online Publication Date: 24 January 2007

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An optical filter based on side coupling between silicon wire waveguide and two-dimensional photonic crystal surface-mode cavity is presented. The design is optimized numerically by parallel three-dimensional finite-different time-domain simulations. The device is then fabricated on amorphous silicon-on-silica structure. The drop wavelength is observed around 1580 nm. The extinction ratio of the filter is larger than 10 dB and the intrinsic quality factor of the surface-mode cavity is approximately 2000.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.15.Eq Optical system design

Cavity resonances in finite plasmonic chains

P. Ghenuche, I. G. Cormack, G. Badenes, P. Loza-Alvarez, and R. Quidant

Appl. Phys. Lett. 90, 041109 (2007); http://dx.doi.org/10.1063/1.2435513 (3 pages) | Cited 10 times

Online Publication Date: 24 January 2007

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The authors report on the observation of cavity resonances along finite gold nanoparticle chains which, unlike continuous gold nanowires, lead to a high field concentration at their extremity. The mode signature has been assessed by probing the local field bound to the metal with two-photon luminescence spectroscopy. Simulations based on the Green dyadic method corroborate a good agreement with the measurements and bring further insight to the physics involved.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
78.55.Hx Other solid inorganic materials
73.22.Lp Collective excitations

Effect of temporal pulse shape on optical damage

C. W. Carr, J. B. Trenholme, and M. L. Spaeth

Appl. Phys. Lett. 90, 041110 (2007); http://dx.doi.org/10.1063/1.2431705 (3 pages) | Cited 18 times

Online Publication Date: 25 January 2007

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The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. The authors present here data from a simple single-parameter model and a supporting experiment which predicts that a flat-in-time pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same duration.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Generation of continuous-wave broadband entangled beams using periodically poled lithium niobate waveguides

Ken-ichiro Yoshino, Takao Aoki, and Akira Furusawa

Appl. Phys. Lett. 90, 041111 (2007); http://dx.doi.org/10.1063/1.2437057 (3 pages) | Cited 11 times

Online Publication Date: 25 January 2007

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Continuous-wave light beams with broadband quantum entanglement are created with two independent squeezed light beams generated by two periodically poled lithium niobate waveguides and a symmentric beam splitter. The quantum entanglement is confirmed with a sufficient criterion ΔA,B2 = 〈[Δ(mathA−mathB)]2〉+〈[Δ(mathA+mathB)]2〉<1 and the observed ΔA,B2 is 0.75 over the bandwidth of 30 MHz. Although the bandwidth is limited by that of the detector so far, it would be broadened up to 10 THz which would be only limited by the bandwidth of phase matching for the second-order nonlinear process.
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03.67.Mn Entanglement measures, witnesses, and other characterizations
42.50.Dv Quantum state engineering and measurements
42.65.Lm Parametric down conversion and production of entangled photons

Terahertz quantum-cascade lasers based on a three-well active module

H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao

Appl. Phys. Lett. 90, 041112 (2007); http://dx.doi.org/10.1063/1.2437071 (3 pages) | Cited 57 times

Online Publication Date: 25 January 2007

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The authors report on a design of terahertz quantum-cascade lasers based on three-well active modules. Each module consists of two tunnel-coupled wells for the two lasing states and another well for both resonant-phonon depopulation and carrier injection. This design is the simplest so far among the various published working devices. The test device has a lasing frequency of 3.4 THz and maximum operating temperature of 142 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Wave front evolution of negatively refracted waves in a photonic crystal

Ethan Schonbrun, Qi Wu, Wounjhang Park, Tsuyoshi Yamashita, Christopher J. Summers, Maxim Abashin, and Yeshaiahu Fainman

Appl. Phys. Lett. 90, 041113 (2007); http://dx.doi.org/10.1063/1.2435344 (3 pages) | Cited 14 times

Online Publication Date: 25 January 2007

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Using a heterodyne near-field scanning microscope, the authors analyze the phase and amplitude of the electric field of an optical wave across the boundary of positive to negative refraction media. The photonic crystal acts as an extremely anisotropic material with a negative curvature of its dispersion surface whose shape is resolved experimentally. This extreme anisotropy results in the beam having a peculiar phase evolution through propagation that does not occur in isotropic media. A focusing wave is produced by negative refraction, which has diverging wave fronts before the internal focus and converging wave fronts after the focus.
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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)

Tomographic reconstruction of picosecond acoustic strain propagation

Motonobu Tomoda, Osamu Matsuda, Oliver B. Wright, and Roberto Li Voti

Appl. Phys. Lett. 90, 041114 (2007); http://dx.doi.org/10.1063/1.2432238 (3 pages) | Cited 8 times

Online Publication Date: 26 January 2007

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By means of an ultrafast optical technique, picosecond acoustic strain pulses in a transparent medium are tomographically visualized. The authors reconstruct strain pulses in Au-coated glass from time-domain reflectivity changes as a function of the optical angle of incidence, with ∼ 1 ps temporal and ∼ 100 nm spatial resolutions.
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42.30.Wb Image reconstruction; tomography
78.47.-p Spectroscopy of solid state dynamics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
62.65.+k Acoustical properties of solids

Use of anisotropic laser etching to the top n-GaN layer to alleviate current-crowding effect in vertical-structured GaN-based light-emitting diodes

Tron-Min Chen, Shui-Jinn Wang, Kai-Ming Uang, Shiue-Lung Chen, Wei-Chih Tsai, Wei-Chi Lee, and Ching-Chung Tsai

Appl. Phys. Lett. 90, 041115 (2007); http://dx.doi.org/10.1063/1.2432254 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2007

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To equalize the resistance of all possible current paths in regular vertical-conducting metal-substrate GaN-based light-emitting diodes (VM-LEDs), an anisotropic laser etching to the surface layer (n-GaN) of 40 mil VM-LEDs for improving light emission uniformity and light output power is proposed and demonstrated. The feasibility of the proposed scheme was verified by current and light emission distribution as well as light extraction rate simulations. In conjunction with a nonuniform excimer laser beam irradiation through a mask and rotation of the epitaxy wafer, VM-LEDs with a concave-surface n-GaN layer were also fabricated. Typical improvement in light output power by 38%–26% at an injection current of 350 mA as compared to the one without anisotropic etching has been obtained.
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85.60.Jb Light-emitting devices
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