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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Efficient pure-white organic light-emitting diodes with a solution-processed, binary-host employing single emission layer

Jwo-Huei Jou, Ming-Chen Sun, Hung-Hsing Chou, and Chien-Hung Li

Appl. Phys. Lett. 88, 141101 (2006); http://dx.doi.org/10.1063/1.2189011 (3 pages) | Cited 25 times

Online Publication Date: 3 April 2006

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Efficient white light-emitting diodes were fabricated with a solution-processed single emission layer composing a molecular and polymeric materials mixed binary host. The main host used was a molecule of 4,4′-bis-(carbazol-9-yl) biphenyl and the assisting host used was a blue light-emitting polyfluorene-derived copolymer of poly[(9,9-dioctylfluo-renyl-2,7-diyl)-alt-co-(9-hexyl-3,6-carbazole)]. The hosts were doped via solution-mixing a green dye of tris(2-phenylpyridine) iridium (III) and a red dye of bis[2-(2′-benzo-thienyl)-pyridi-nato-N,C3,](acetylacetonate) iridium (III). One resultant device having a pure white emission of Commission Internationale de l’Eclairage (0.33, 0.33) has a maximum power efficiency of 4.2 lm/W at 802 cd/m2 and a maximum brightness of 11 800 cd/m2. The better efficiency performance may be attributed to the addition of the assisting host, which halves the energy barrier for holes to inject into the light-emitting zone.
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85.60.Jb Light-emitting devices

Electrically switchable, two-color quantum cascade laser emitting at 1.39 and 2.3 THz

Giacomo Scalari, Christoph Walther, Jérôme Faist, Harvey Beere, and David Ritchie

Appl. Phys. Lett. 88, 141102 (2006); http://dx.doi.org/10.1063/1.2191407 (3 pages) | Cited 38 times

Online Publication Date: 3 April 2006

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A quantum cascade laser emitting at 1.39 and 2.3 THz is demonstrated. The structure is based on a large single quantum well and multiwavelength operation is obtained by selectively injecting carriers by resonant tunneling in the excited states of the well. A magnetic field applied perpendicularly to the layers increases the gain enabling laser action. Extremely low values of the threshold current density (below 30 A/cm2) are observed for both wavelengths. A study of the dependence of the laser emission intensity as a function of the applied magnetic field is also presented.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Scanning particle trapped optical microscopy based on two-photon-induced morphology-dependent resonance in a trapped microsphere

Dru Morrish, Xiaosong Gan, and Min Gu

Appl. Phys. Lett. 88, 141103 (2006); http://dx.doi.org/10.1063/1.2186076 (3 pages) | Cited 4 times

Online Publication Date: 3 April 2006

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We report on scanning particle trapped optical microscopy based on two-photon-induced morphology-dependent resonance (MDR) in a trapped microsphere. In this imaging mode, a femtosecond pulsed laser is adopted for simultaneous laser trapping and two-photon excitation. Due to the localized excitation, MDR is significantly enhanced. As a result, an image contrast enhancement of 9.3% is achieved by the spectral detection of a single on-resonance MDR mode compared with that obtained by the off-resonance MDR mode without compromise in transverse resolution.
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07.60.Pb Conventional optical microscopes
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of the nonlinear carrier response time of AlGaAs photonic crystal waveguides by sample design

P. Murzyn, A. Z. Garcia-Deniz, D. O. Kundys, A. M. Fox, J.-P. R. Wells, D. M. Whittaker, M. S. Skolnick, T. F. Krauss, and J. S. Roberts

Appl. Phys. Lett. 88, 141104 (2006); http://dx.doi.org/10.1063/1.2191955 (3 pages) | Cited 8 times

Online Publication Date: 4 April 2006

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We have used reflection geometry pump-probe spectroscopy to investigate the free carrier response time of AlGaAs high refractive index contrast one-dimensional photonic crystal waveguides. We have observed pump-induced shifts of photonic resonances in the near infrared spectral region, and have studied the dependence of the decay time on the sample parameters. We find that the response time can be varied from 8 to 33 ps by changing the structure period and etch depth. This, combined with the large changes observed in the reflectivity, demonstrates excellent potential for application as ultrafast photonic switches with a controllable recovery time.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Cf Surface cleaning, etching, patterning
42.15.Eq Optical system design

High sensitivity surface plasmon resonance sensor based on phase interrogation at optimal incident wavelengths

Hai-Pang Chiang, Jing-Lun Lin, and Zhi-Wei Chen

Appl. Phys. Lett. 88, 141105 (2006); http://dx.doi.org/10.1063/1.2192622 (3 pages) | Cited 7 times

Online Publication Date: 4 April 2006

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It is demonstrated that ultrahigh sensitivity of glucose refractive index measurement can be achieved via surface plasmon resonance excitation in which the phase difference between p- and s-polarized reflected waves is monitored as a function of the incident angle. Sensitivity with values down to the order of 10−8 is obtained by performing the measurements at optimal incident wavelengths. This represents an order of magnitude improvement compared to the previously reported values in the literature.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
07.60.Hv Refractometers and reflectometers

Spatial and temporal sensitivity variations in photorefractive electro-optic field sensors

A. Garzarella, S. B. Qadri, Terence J. Wieting, and Dong Ho Wu

Appl. Phys. Lett. 88, 141106 (2006); http://dx.doi.org/10.1063/1.2192980 (2 pages) | Cited 6 times

Online Publication Date: 5 April 2006

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Experimental studies of the spatial and temporal fluctuations in photorefractive electro-optic (EO) field sensors have revealed that their maximum intrinsic responsivity is limited by incoherence in the polarization of the probe beam. This incoherence is generated within the irradiated crystal itself. We describe a novel method to measure the incoherence directly while suppressing the temporal fluctuations. Our results indicate that optically induced distributions of birefringence (photorefractivity) generally impair the modulating ability of EO crystals.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Scanning near-field optical microscopy images of microradiographs stored in lithium fluoride films with an optical resolution of λ/12

Alessandro Ustione, Antonio Cricenti, Francesca Bonfigli, Francesco Flora, Antonella Lai, Tiziana Marolo, Rosa Maria Montereali, Giuseppe Baldacchini, Anatoly Faenov, Tatiana Pikuz, and Lucia Reale

Appl. Phys. Lett. 88, 141107 (2006); http://dx.doi.org/10.1063/1.2193654 (3 pages) | Cited 17 times

Online Publication Date: 6 April 2006

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Here we show a new, simple method to observe soft x-ray microradiographs of biological material. A thin film of lithium fluoride (LiF) works as image detector, storing the microradiograph obtained exposing biological samples to extreme ultraviolet and soft x-ray radiations. To read the stored image, collecting the optically stimulated visible luminescence emitted by the LiF active color centers locally produced by the x rays, a scanning near-field optical microscope is used with an optical aperture of 50 nm, i.e., λ/12, where λ is the wavelength of the collected photoluminescence.
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87.64.mt Near-field scanning
42.79.Pw Imaging detectors and sensors
61.72.J- Point defects and defect clusters
78.55.Hx Other solid inorganic materials

Localized excitation of InGaAs quantum dots by utilizing a photonic crystal nanocavity

Masahiro Nomura, Satoshi Iwamoto, Toshihiro Nakaoka, Satomi Ishida, and Yasuhiko Arakawa

Appl. Phys. Lett. 88, 141108 (2006); http://dx.doi.org/10.1063/1.2193811 (3 pages) | Cited 3 times

Online Publication Date: 6 April 2006

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We have studied excitation wavelength dependence of light emission from InGaAs quantum dots (QDs) embedded in high-quality-factor photonic crystal nanocavities. The light emission of the cavity mode around 1 μm was very weak with below-band-gap excitation in the InGaAs wetting layer. However, the emission of the lowest-order cavity mode was strongly enhanced when the excitation wavelength was resonant with higher-order cavity modes. This phenomenon can be attributed to the local intensity enhancement of the excitation light which couples with the cavity mode. The on-resonant excitation technique selectively and efficiently excites only the QDs in the cavity without undesirable background emission.
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78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.70.Qs Photonic bandgap materials

Variable optical reflectance of a self-supported Si grating

Kazuhiro Hane, Takashi Kobayashi, Fang-Ren Hu, and Yoshiaki Kanamori

Appl. Phys. Lett. 88, 141109 (2006); http://dx.doi.org/10.1063/1.2193989 (3 pages) | Cited 14 times

Online Publication Date: 6 April 2006

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Variable reflectance of a self-supported Si grating mirror is reported. A grating suspended in air consisted of an array of 300 nm wide, 300 nm thick, and 20 μm long beams. The period of the grating was varied with an electrostatic microactuator from 600 to 720 nm. A broadband reflection in the wavelength longer than the grating period was observed, which was caused by a resonant interference of the light wave propagating along the grating similar to the guided-mode resonant gratings. Increasing the period of the grating with a microactuator, the reflection spectrum changed. The results were explained by the theoretical calculations based on rigorous coupled-wave analysis.
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42.79.Dj Gratings
42.82.Gw Other integrated-optical elements and systems
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Internal-friction mapping on solids by resonance ultrasound microscopy

H. Ogi, H. Niho, and M. Hirao

Appl. Phys. Lett. 88, 141110 (2006); http://dx.doi.org/10.1063/1.2194479 (3 pages) | Cited 7 times

Online Publication Date: 6 April 2006

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An internal-friction microscopy is developed for quantitatively determining material damping on a local surface area by measuring vibrational attenuation of an isolated langasite oscillator point contacting the material. Noncontacting measurement of the resonance frequency and attenuation coefficient of the longitudinal vibration of the oscillator has been achieved with a line antenna, providing high sensitivity to the modulus and damping in the local contacting area. Formulation of the relationship between a material’s local internal friction and attenuation of the resonator system is proposed using the generalized Hertzian-contact model. Results on a dual-phase stainless steel and a Cu/NbTi composite are shown.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.37.Tj Acoustic force microscopy

Laser trapping of ice crystals

Kazuki Taji, Maki Tachikawa, and Kazushige Nagashima

Appl. Phys. Lett. 88, 141111 (2006); http://dx.doi.org/10.1063/1.2190074 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2006

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Toward application to crystal physics, we demonstrate optical trapping of ice crystals as well as supercooled water droplets using counterpropagating laser beams. Confinement of an ice crystal is evidenced by the angular distribution of laser light deflected from the crystal faces. The average trap time, limited by air currents, is 5 s for ice crystals and much longer for water drops.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
64.70.D- Solid-liquid transitions

Cesium vapor laser pumped by a volume-Bragg-grating coupled quasi-continuous-wave laser-diode array

You Wang, Tadashi Kasamatsu, Yujin Zheng, Hirofumi Miyajima, Hirotake Fukuoka, Shinichi Matsuoka, Minoru Niigaki, Hiroyuki Kubomura, Teruo Hiruma, and Hirofumi Kan

Appl. Phys. Lett. 88, 141112 (2006); http://dx.doi.org/10.1063/1.2192975 (3 pages) | Cited 22 times

Online Publication Date: 7 April 2006

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The experimental demonstration of a broad-area Quasi-continuous-wave (QCW) laser-diode array pumped cesium vapor laser is reported in this letter according to our experimental results. We used a volume-Bragg grating to narrow the spectral linewidth for acquirement of enough resonance transitions. A glass cylindrical cell filled with cesium/buffer gas was set in an end-pumped flat-concave cavity and the gas pressure was set lower than 1 atm. Using the QCW drive mode with the repetitive rate and pulse width of 1 kHz and 50 μs, respectively, 13.45 μJ pulse energy has been achieved with the slope efficiency of about ∼ 1.8%.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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