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28 Apr 2003

Volume 82, Issue 17, pp. 2749-2924

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Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Three-level picture for chirp-dependent fluorescence yields under femtosecond optical pulse irradiation

Naoyuki T. Hashimoto, Kazuhiko Misawa, and Roy Lang

Appl. Phys. Lett. 82, 2749 (2003); http://dx.doi.org/10.1063/1.1571225 (3 pages) | Cited 4 times

Online Publication Date: 21 April 2003

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We propose a simple model to account for chirp-dependent fluorescence yields from a substance under femtosecond optical pulse irradiation. The model is simple, consisting of a three-level system, and yet it explains the essential feature of the chirp-dependent fluorescence yields experimentally observed, for example, with cyanine dye molecules. Based on the model, the dependence of the fluorescence on the excitation pulse properties such as the chirp rate and pulse intensity has been examined in detail. The results indicate that chirp-dependent fluorescence can be utilized as a convenient means for characterizing phase distortions in optical pulses such as those in optical fiber communication systems. © 2003 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.-p Quantum optics
78.55.-m Photoluminescence, properties and materials

Multimode combined intense laser-induced electron acceleration and violent bunch compression

P. X. Wang, Ch. X. Tang, and Sh. J. Huang

Appl. Phys. Lett. 82, 2752 (2003); http://dx.doi.org/10.1063/1.1569417 (3 pages) | Cited 6 times

Online Publication Date: 21 April 2003

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The ponderomotive potential structure of a multimode combined intense laser beam is studied. Using a three-dimensional test particle simulation, the interaction of slow electrons with the combined laser beam in vacuum is investigated. The calculation shows that electrons distributed on a large scale can be accelerated to relativistic energy in vacuum. A violent longitudinal bunch compression phenomenon is also presented and discussed. © 2003 American Institute of Physics.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Ah General laser theory
41.60.Cr Free-electron lasers

Carrier leakage in InGaN quantum well light-emitting diodes emitting at 480 nm

I. A. Pope, P. M. Smowton, P. Blood, J. D. Thomson, M. J. Kappers, and C. J. Humphreys

Appl. Phys. Lett. 82, 2755 (2003); http://dx.doi.org/10.1063/1.1570515 (3 pages) | Cited 55 times

Online Publication Date: 21 April 2003

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Pulsed light–current characteristics of InGaN/GaN quantum well light-emitting diodes have been measured as a function of temperature, with sublinear behavior observed over the whole temperature range, 130–330 K. A distinctive temperature dependence is also noted where the light output, at a fixed current, initially increases with temperature, before reaching a maximum at 250 K and then decreases with subsequent increases in temperature. On the basis of a drift diffusion model, we can explain the sublinear light–current characteristics and the temperature dependence by the influence of the large acceptor ionization energy in Mg-doped GaN together with a triangular density of states function characteristic of localized states. Without the incorporation of localization effects, we are unable to reproduce the temperature dependence whilst maintaining emission at the observed wavelength. This highlights the importance of localization effects on device performance. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells
78.67.De Quantum wells
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.Fz Weak or Anderson localization

Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses

Toshiaki Kondo, Shigeki Matsuo, Saulius Juodkazis, Vygantas Mizeikis, and Hiroaki Misawa

Appl. Phys. Lett. 82, 2758 (2003); http://dx.doi.org/10.1063/1.1569987 (3 pages) | Cited 49 times

Online Publication Date: 21 April 2003

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Femtosecond laser pulses are useful for laser microfabrication through multiphoton absorption. However, it is difficult to create interference of femtosecond pulses for the fabrication of periodic structures. In this letter, we report the fabrication of two-dimensional periodic structures by means of multibeam interference of femtosecond pulses. Scanning electron microscopy revealed a rod structure arranged into a square lattice. The possibility of controlling the period of the lattice, rod thickness, and rod shape were demonstrated. © 2003 American Institute of Physics.
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42.62.Cf Industrial applications
81.20.Wk Machining, milling
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Increasing shear force microscopy scanning rate using active quality-factor control

M. Antognozzi, M. D. Szczelkun, A. D. L. Humphris, and M. J. Miles

Appl. Phys. Lett. 82, 2761 (2003); http://dx.doi.org/10.1063/1.1571233 (3 pages) | Cited 13 times

Online Publication Date: 21 April 2003

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The use of an active quality-factor control device has been demonstrated to increase the scanning rate of a shear force microscope by lowering the quality factor of the oscillating probe. Shear force microscopy (often used in combination with scanning near-field optical microscopy) requires slow scanning rates due to the long (>1 ms) time constant of the oscillating element (optical fiber or tuning fork). By electronically reducing the quality factor of the probe, it was possible to tune the time constant and correspondingly reduce the overall scanning time by a factor of 4. It was also seen that probes with high quality factors could manifest an unstable behavior; by reducing the quality factor of the probe, it was possible to increase the signal-to-noise ratio and so improve the imaging resolution. Deoxyribonucleic acid molecules deposited onto mica and imaged in air were used to demonstrate the technique. © 2003 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
87.64.Dz Scanning tunneling and atomic force microscopy
87.14.G- Nucleic acids

Efficient blue light-emitting diodes with InGaN/GaN triangular shaped multiple quantum wells

R. J. Choi, Y. B. Hahn, H. W. Shim, M. S. Han, E. K. Suh, and H. J. Lee

Appl. Phys. Lett. 82, 2764 (2003); http://dx.doi.org/10.1063/1.1570511 (3 pages) | Cited 9 times

Online Publication Date: 21 April 2003

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InGaN/GaN triangular shaped multiple quantum wells (QWs) grown by grading In composition with time were adopted as an active layer of blue light-emitting diodes (LEDs). Compared to the LEDs with conventional rectangular QW structures, the triangular QW LEDs showed a higher intensity and a narrower linewidth of electrical luminescence (EL), a lower operation voltage, and a stronger light-output power. EL spectra of the triangular-QW-based LEDs also showed that the peak energy is nearly independent of the injection current and temperature, indicating that the triangular QW LED is more efficient and stable than the rectangular one. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence

Tunable photonic crystals fabricated in III-V semiconductor slab waveguides using infiltrated liquid crystals

Ch. Schuller, F. Klopf, J. P. Reithmaier, M. Kamp, and A. Forchel

Appl. Phys. Lett. 82, 2767 (2003); http://dx.doi.org/10.1063/1.1570921 (3 pages) | Cited 56 times

Online Publication Date: 21 April 2003

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Microcavity structures formed by two-dimensional photonic crystal mirrors with triangular lattice and a crystal period of 280 nm suitable for transmission experiments at about 1 μm were fabricated in III-V semiconductor planar waveguides. The photonic crystals were filled with a liquid crystal of type E7. The wavelength of the resonance peak can be shifted by the temperature-dependent refractive index of the liquid crystal. The temperature shift follows the typical refractive index behavior of liquid crystals, with a jump in wavelength at the clearing point (about 60 °C) and a continuous shift below. The wavelength jump is about 4 nm within a few Kelvin, while the total shift amounts to 9 nm between 20 and 70 °C. The experimental results agree well with the calculated temperature dependent photonic band structure by assuming a preferential alignment of the liquid-crystal molecules parallel to the holes. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
42.65.Wi Nonlinear waveguides
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

GaAs-based near-infrared omnidirectional reflector

Yeonsang Park, Young-Geun Roh, Chi-O Cho, Heonsu Jeon, Min Gyu Sung, and J. C. Woo

Appl. Phys. Lett. 82, 2770 (2003); http://dx.doi.org/10.1063/1.1569045 (3 pages) | Cited 19 times

Online Publication Date: 21 April 2003

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We introduce a compound-semiconductor-based omnidirectional reflector. A four-layer-pair stack of GaAs/AlAs was grown epitaxially using molecular-beam epitaxy, and was then converted to a GaAs/Al2O3 multilayer stack by selective oxidation of the AlAs layers. The resultant one-dimensional photonic crystal exhibited omnidirectional reflection properties in near-IR wavelength range below 1 μm. Reflectance spectra measured at various incidence angles and polarizations were observed to be in good agreement with theoretically simulated results. © 2003 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
78.30.Fs III-V and II-VI semiconductors
81.65.Mq Oxidation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Semiconductor mirror for dynamic dispersion compensation

A. Isomäki, A. Vainionpää, J. Lyytikäinen, and O. G. Okhotnikov

Appl. Phys. Lett. 82, 2773 (2003); http://dx.doi.org/10.1063/1.1569990 (2 pages) | Cited 3 times

Online Publication Date: 21 April 2003

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We report on a monolithic Gires–Tournois semiconductor interferometer used to generate a tunable delay. Controllable saturable absorption in optically pumped multiple-quantum-well semiconductor reflector was shown to provide promising means for rapid changing the group delay of the reflector, and represents an attractive form of dynamic dispersion compensation. © 2003 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
78.67.De Quantum wells
81.07.St Quantum wells
07.60.Ly Interferometers
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.82.Gw Other integrated-optical elements and systems
42.65.-k Nonlinear optics

Lens-free heterodyne detection for transient grating experiments

K. Katayama, M. Yamaguchi, and T. Sawada

Appl. Phys. Lett. 82, 2775 (2003); http://dx.doi.org/10.1063/1.1569051 (3 pages) | Cited 28 times

Online Publication Date: 21 April 2003

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An enhanced technique of heterodyne detection for transient grating experiments has been developed. This technique features a very simple optical alignment because no lenses are used to focus beams on the samples. It was applied to a vapor-deposited gold thin film (thickness: 30 nm), and the detected signal was confirmed to consist of a heterodyne component based on the dependence of the signal intensity on the pump intensity. Furthermore, this technique was shown to provide easy control of the phase difference between the probe and reference beams. © 2003 American Institute of Physics.
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42.79.Dj Gratings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Tuning of the blue emission from europium-doped alkaline earth chloroborate thin films activated in air

Jianhua Hao, J. Gao, and Michael Cocivera

Appl. Phys. Lett. 82, 2778 (2003); http://dx.doi.org/10.1063/1.1569048 (3 pages) | Cited 14 times

Online Publication Date: 21 April 2003

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Thin films of M2B5O9Cl:Eu (M = Ca, Sr, Ba) were prepared on glass substrates using spray pyrolysis. Blue cathodoluminescence due to the abnormal reduction of Eu3+→Eu2+ was obtained by annealing films in air. The cation of the host lattice was found to affect the effectiveness of the reduction process, which could result in influencing the emission band. By selecting types and composition of alkaline cation, it was possible to tune the dominant emitting wavelength between 435 to 465 nm. Activation of the films occurred at temperatures suitable for the use of glass substrates. © 2003 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Nk Insulators
68.55.Nq Composition and phase identification
71.55.Ht Other nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
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