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18 Jul 2005

Volume 87, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 87, 033501 (2005); http://dx.doi.org/10.1063/1.1992665 (3 pages)

Yoshihito Miyoshi, Fumito Nakajima, Junichi Motohisa, and Takashi Fukui
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Variable holographic femtosecond laser processing by use of a spatial light modulator

Yoshio Hayasaki, Takashi Sugimoto, Akihiro Takita, and Nobuo Nishida

Appl. Phys. Lett. 87, 031101 (2005); http://dx.doi.org/10.1063/1.1992668 (3 pages) | Cited 7 times

Online Publication Date: 11 July 2005

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We propose a holographic femtosecond laser processing system capable of parallel, arbitrary, and variable patterning. These features are achieved by introducing a spatial light modulator displaying a hologram into the femtosecond laser processing system. We demonstrate the variable parallel processing of a glass sample.
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42.40.Jv Computer-generated holograms
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.86.+b Optical workshop techniques
42.62.-b Laser applications
42.79.Hp Optical processors, correlators, and modulators
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Double interference fluorescence enhancement from reflective slides: Application to bicolor microarrays

H. Choumane, N. Ha, C. Nelep, A. Chardon, G. O. Reymond, C. Goutel, G. Cerovic, F. Vallet, C. Weisbuch, and H. Benisty

Appl. Phys. Lett. 87, 031102 (2005); http://dx.doi.org/10.1063/1.1999018 (3 pages) | Cited 17 times

Online Publication Date: 11 July 2005

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A technique for enhancing fluorescence from species close to a substrate is described, based on a multilayer dielectric mirror coating. For proper design, interferences bring improvements to both fluorescence excitation and collection, each about four fold. The overall improvement reaches 10 to 15 fold as compared to a standard glass slide. We apply this to so-called deoxyribonucleic acid (DNA) chips, that is to DNA hybridization assays on microarray platforms, for which two fluorophores most commonly used are cyanine dyes (Cy3™ and Cy5™). Impact of the two-color scheme is discussed. A validation method based on spin-coated fluorescent ultrathin layers is shown to accurately determine the amplification factors of the different tagging dyes.
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87.80.-y Biophysical techniques (research methods)
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics
87.15.-v Biomolecules: structure and physical properties
87.14.G- Nucleic acids
42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings

Polarization mode splitting in monolithic polymer microcavities

Luana Persano, Elisa Mele, Roberto Cingolani, and Dario Pisignano

Appl. Phys. Lett. 87, 031103 (2005); http://dx.doi.org/10.1063/1.1994956 (3 pages) | Cited 12 times

Online Publication Date: 11 July 2005

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We demonstrate the mode splitting of the resonant emission from a symmetric monolithic organic semiconductor microcavity. The device, realized by low-temperature reactive electron-beam evaporation and deposition of a conjugated polymer, exhibits a 100 meV polarization-induced splitting of the transmission and emission resonances for angles larger than 45°. This opens the way for the realization of novel polarized-emitting optoelectronic devices based on plastic materials.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.60.-q Optoelectronic devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Polyfluorene distributed feedback lasers operating in the green-yellow spectral region

R. Xia, G. Heliotis, P. N. Stavrinou, and D. D. C. Bradley

Appl. Phys. Lett. 87, 031104 (2005); http://dx.doi.org/10.1063/1.1994928 (3 pages) | Cited 32 times

Online Publication Date: 11 July 2005

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We report solid-state, optically pumped poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), distributed feedback lasers that operate in the green-yellow spectral region, previously unaddressed with conjugated polymer gain media. The lasers were fabricated by spin coating F8BT (the gain medium) onto one-dimensional gratings patterned in silica substrates. The emission wavelength could be selected to lie within the range from 558 to 591 nm by controlling the F8BT film thickness and grating periodicity. The minimum lasing threshold of 6.5 nJ per pump pulse (10 ns, 10 Hz, 450 nm) was achieved for a 350 nm spatial period grating with a 180 nm thickness F8BT film. The corresponding emission wavelength was 573 nm and the laser slope efficiency was a relatively high 3%.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Dj Gratings
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

High-quality factor optical microcavities using oxide apertured micropillars

N. G. Stoltz, M. Rakher, S. Strauf, A. Badolato, D. D. Lofgreen, P. M. Petroff, L. A. Coldren, and D. Bouwmeester

Appl. Phys. Lett. 87, 031105 (2005); http://dx.doi.org/10.1063/1.1999843 (3 pages) | Cited 13 times

Online Publication Date: 12 July 2005

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An oxide aperture is used to confine optical modes in a micropillar structure. This method overcomes the limitations due to sidewall scattering loss typical in semiconductor etched micropillars. High cavity quality factors (Q) up to 48 000 are determined by external Fabry–Perot cavity scanning measurements, a significantly higher value than prior work in III-V etched micropillars. Measured Q values and estimated mode volumes correspond to a maximum Purcell factor figure of merit value of 72.
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85.30.-z Semiconductor devices

Efficient continuous-wave holey fiber Raman laser

J. C. Travers, S. V. Popov, and J. R. Taylor

Appl. Phys. Lett. 87, 031106 (2005); http://dx.doi.org/10.1063/1.2000328 (3 pages) | Cited 9 times

Online Publication Date: 13 July 2005

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A continuous wave Raman laser, with only 100 m of holey fiber as the Raman gain medium, is reported in a linear cavity all-fiber configuration. Slope efficiencies of 29% with a threshold of 2.7 W and 77% with a threshold of 3.7 W were achieved with a maximum output power of 3.6 W at 1.12 μm. The estimated holey fiber Raman gain coefficient of ∼ 17 W−1 km−1 is over 40 times larger than that of a standard telecommunication fiber.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Highly efficient and stable luminescence of nanocrystalline porous silicon treated by high-pressure water vapor annealing

B. Gelloz, A. Kojima, and N. Koshida

Appl. Phys. Lett. 87, 031107 (2005); http://dx.doi.org/10.1063/1.2001136 (3 pages) | Cited 55 times

Online Publication Date: 14 July 2005

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The effects of a treatment based on high-pressure water vapor annealing (HWA) on nanocrystalline porous silicon have been investigated in terms of the photoluminescence (PL) efficiency and stability. For originally nonluminescent samples with a relatively low porosity, the treatment produces highly efficient and stable luminescent nanocrystalline-Si (nc-Si) layers without affecting the emission wavelength. Under appropriate conditions of pressure (2.6 MPa) and temperature (260 °C), the PL external quantum efficiency reaches 23% at room temperature. Electron-spin-resonance and infrared absorption analyses show that the HWA treatment promotes surface oxidation of nc-Si under a minimized mechanical stress and consequently generates sufficiently passivated nc-Si/SiO2 interfaces with an extremely low nonradiative defect density. This causes a drastic enhancement in the PL efficiency associated with a strong localization of excitons in nc-Si. As a practical approach, the HWA technique is very useful for fabrication of efficient and stable optoelectronic nc-Si devices.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.05.Rm Porous materials; granular materials
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
71.35.-y Excitons and related phenomena
73.22.Lp Collective excitations
62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment
61.46.-w Structure of nanoscale materials
81.65.Mq Oxidation
81.16.Pr Micro- and nano-oxidation
76.30.Da Ions and impurities: general
61.43.Gt Powders, porous materials
78.55.Mb Porous materials

Investigation of strontium silicate yellow phosphors for white light emitting diodes from a combinatorial chemistry

Joung Kyu Park, Kyoung Jae Choi, Kyoung Nam Kim, and Chang Hae Kim

Appl. Phys. Lett. 87, 031108 (2005); http://dx.doi.org/10.1063/1.1984103 (3 pages) | Cited 23 times

Online Publication Date: 14 July 2005

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In order to develop yellow phosphors that emit efficiently under the 450–470 nm excitation range, combinatorial chemistry was used based on silicate materials and investigated in an attempt to develop white light-emitting diodes (LEDs) by combining it with an InGaN blue LED chip (460 nm). Quaternary and ternary combinatorial libraries were developed to synthesize, process, and screen for silicate materials. Our combinatorial chemistry system consists of solution-based combinatorial synthesis and characterization, enabling the swift scanning of luminance. As a consequence of the combinatorial approach, several candidates were found to show high luminance under the 450–470 nm excitation range.
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85.60.Jb Light-emitting devices

Single-mode vertical-cavity surface-emitting laser with ring-shaped light-emitting aperture

Jin-Wei Shi, C.-H. Jiang, K.-M. Chen, J.-L. Yen, and Ying-Jay Yang

Appl. Phys. Lett. 87, 031109 (2005); http://dx.doi.org/10.1063/1.1997282 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2005

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In this letter, we demonstrate a single-mode vertical-cavity surface-emitting laser (VCSEL) with a ring-shaped light-emitting aperture, which is realized by the Zn diffusion technique, at a wavelength of 850 nm. Relative to the control VCSEL with an ordinary circular aperture and the same geometry and size, the demonstrated device can suppress the higher-order transverse mode more effectively without affecting the threshold current and output power. Compared with typical reported single-mode VCSELs, a larger light-emitting aperture and current-confined area with a smaller divergence angle of the output beam, and lower differential resistance are achieved with the present structure.
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42.55.Px Semiconductor lasers; laser diodes

High-definition vertically aligned liquid crystal microdisplays using a circularly polarized light

Kuan-Hsu Fan-Chiang, Shu-Hsia Chen, and Shin-Tson Wu

Appl. Phys. Lett. 87, 031110 (2005); http://dx.doi.org/10.1063/1.1999837 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2005

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A high-definition vertically aligned liquid crystal (LC) microdisplay exhibits a excellent contrast ratio, but its fringing field effect splits the bright state unevenly and leads to a very slow response time. By utilizing a circularly polarized light instead of conventional linearly polarized light, we have overcome the long-standing problems of poor sharpness, low brightness, and slow response time. Confirming computer simulations agree with the experimental results well. This approach can be applied to both reflective and transmissive LC microdisplays.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Internal high-reflectivity omni-directional reflectors

J.-Q. Xi, Manas Ojha, J. L. Plawsky, W. N. Gill, Jong Kyu Kim, and E. F. Schubert

Appl. Phys. Lett. 87, 031111 (2005); http://dx.doi.org/10.1063/1.1997270 (3 pages) | Cited 21 times

Online Publication Date: 15 July 2005

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An internal high-reflectivity omni-directional reflector (ODR) for the visible spectrum is realized by the combination of total internal reflection using a low-refractive-index (low-n) material and reflection from a one-dimensional photonic crystal (1D PC). The low-n layer limits the range of angles in the 1D PC to values below the Brewster angle, thereby enabling high reflectivity and omni-directionality. This ODR is demonstrated using GaP as ambient, nanoporous SiO2 with a very low refractive index (n = 1.10), and a four-pair TiO2/SiO2 multilayer stack. The results indicate a two orders of magnitude lower angle-integrated transverse-electric-transverse-magnetic polarization averaged mirror loss of the ODR compared with conventional distributed Bragg reflectors and metal reflectors. This indicates the high potential of the internal ODRs for optoelectronic semiconductor devices, e.g., light-emitting diodes.
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42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Optical-feedback-induced stability and instability in broad-area semiconductor lasers

Yasuhiro Fujita and Junji Ohtsubo

Appl. Phys. Lett. 87, 031112 (2005); http://dx.doi.org/10.1063/1.1999850 (3 pages) | Cited 4 times

Online Publication Date: 15 July 2005

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Stable and unstable oscillations of broad-area semiconductor laser with optical feedback are experimentally examined. We observe stable oscillations and also coexistent states between stable oscillations and low-frequency fluctuations depending on the feedback positions of the laser beam in the active layer. The laser shows single mode operations both for the oscillation frequency and the spatial mode when it is stabilized.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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