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17 Jul 2000

Volume 77, Issue 3, pp. 313-459

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Characterizing the hard x-ray diffraction properties of a GaAs linear Bragg–Fresnel lens

Youli Li, Gerard C. L. Wong, Ryan Case, Cyrus R. Safinya, Ernie Caine, Evelyn Hu, and Partricia Fernandez

Appl. Phys. Lett. 77, 313 (2000); http://dx.doi.org/10.1063/1.126961 (3 pages) | Cited 4 times

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We investigated the diffractive focusing properties of (111) GaAs linear Bragg–Fresnel lenses (BFLs) developed for hard x-ray microscopy and microdiffraction of complex materials in confined geometries. We demonstrated that the use of GaAs yields significant processing advantages due to the reduced zone depth. Focal plane diffraction patterns of linear BFLs measured at the advanced photon source using 8–40 keV x rays were compared to a simple model based on Kirchhoff–Fresnel diffraction theory. Good agreement was obtained between experimental data and model calculations using only zones within an effective aperture defined by the transverse coherence of the source. © 2000 American Institute of Physics.
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07.85.Tt X-ray microscopes
42.79.Bh Lenses, prisms and mirrors
42.25.Fx Diffraction and scattering

Solar-blind AlGaN-based inverted heterostructure photodiodes

E. J. Tarsa, P. Kozodoy, J. Ibbetson, B. P. Keller, G. Parish, and U. Mishra

Appl. Phys. Lett. 77, 316 (2000); http://dx.doi.org/10.1063/1.126962 (3 pages) | Cited 39 times

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True solar-blind operation with a sharp responsivity cutoff at ∼300 nm has been demonstrated in AlGaN-based photodiodes using an “inverted heterostructure photodiode” design. This structure utilizes an AlxGa1−xN(x>0.3) intrinsic or lightly doped active layer surrounded by p- and/or n-type contact layers having a narrower band gap than the active layer. By utilizing narrow band gap (e.g., GaN) contact layers, the difficulties associated with achieving high doping efficiencies in wide band gap contact layers are circumvented. This basic structure is applicable to both front- and back-side illuminated detector geometries. Front-side illuminated solar-blind photodiodes were demonstrated with a peak responsivity of 0.08 A/W at 285 nm, while back-side illuminated detectors yielded a peak responsivity of 0.033 A/W at 275 nm (both are measured without antireflection coating). Both types of detectors offered sharp spectral responsivity cutoff of at least three orders of magnitude by 325 nm. © 2000 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide

Valentina S. U. Fazio, Sven T. Lagerwall, Philippe Busson, Anders Hult, and Hubert Motschmann

Appl. Phys. Lett. 77, 319 (2000); http://dx.doi.org/10.1063/1.126963 (3 pages) | Cited 3 times

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True phase-matched second-harmonic generation in a waveguide of crosslinkable ferroelectric liquid crystals is demonstrated. These materials allow the formation of macroscopically polar structures whose order can be frozen by photopolymerization. Homeotropic alignment was chosen which offers decisive advantages compared to other geometries. All parameters contributing to the conversion efficiency are maximized by deliberately controlling the supramolecular arrangement. The system has the potential to achieve practical level of performances as a frequency doubler for low power laser-diodes. © 2000 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.79.Kr Display devices, liquid-crystal devices
42.79.Nv Optical frequency converters

Electron drift mobility in pyrazolo[3,4-b]quinoline doped polystyrene layers

A. R. Tameev, Z. He, G. H. W. Milburn, A. A. Kozlov, A. V. Vannikov, A. Danel, and P. Tomasik

Appl. Phys. Lett. 77, 322 (2000); http://dx.doi.org/10.1063/1.126964 (3 pages) | Cited 10 times

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Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5 cm2/(V s) at an electric field of (1–7)×105 V/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account. © 2000 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
71.20.Rv Polymers and organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance

High-frequency properties of 1.55 μm laterally complex coupled distributed feedback lasers fabricated by focused-ion-beam lithography

S. Rennon, L. Bach, J. P. Reithmaier, A. Forchel, J. L. Gentner, and L. Goldstein

Appl. Phys. Lett. 77, 325 (2000); http://dx.doi.org/10.1063/1.126965 (3 pages) | Cited 9 times

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Laterally complex coupled distributed feedback lasers have been fabricated by focused-ion-beam lithography on completely grown InGaAsP/InP laser structures emitting at 1.55 μm. The grating definition is based on implantation-enhanced quantum-well intermixing and wet chemical etching and allows the fabrication of complex coupled antiphase gratings without any further overgrowth step. Side-mode suppression ratios of 45 dB and bandwidths for direct modulation beyond 13 GHz were obtained for 300-μm-long devices. The lasers exhibit frequency-modulation response values lower than 200 MHz/mA and feature a low sensitivity to back-reflected light. Preliminary lifetime measurements over 7000 h continuous-wave operation at room temperature show no significant indication for long-time degradation. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings

Photoluminescence studies and read/write process of a strong two-photon absorbing chromophore

R. Sivaraman, S. J. Clarson, B. K. Lee, A. J. Steckl, and B. A. Reinhardt

Appl. Phys. Lett. 77, 328 (2000); http://dx.doi.org/10.1063/1.126966 (3 pages) | Cited 11 times

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The optical properties of a fluorene-based chromophore exhibiting a high two-photon absorption cross section have been investigated both in the pure state and as a guest–host system in poly(N-vinylcarbazole). Upon irradiation with a helium cadmium (He–Cd) laser at 325 nm, the guest–host sample exhibits a blueshift with a maximum emission at 459 nm. Information written onto the samples in the blue can also be read using an Ar+ laser. The chromophore undergoes a chemical change upon irradiation in air, and has been found to no longer exhibit upconversion after this transformation. Infrared analysis of the sample (the chromophore) before and after irradiation was carried out, and the spectra suggest the formation of a new conjugated species. Other applications we have developed using this phenomenon include the successful writing of optical device structures in polymer films where the AF-50 is a guest material. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
42.79.Vb Optical storage systems, optical disks

High-efficiency organic dye-doped polymer optical fiber lasers

Ken Kuriki, Takeyuki Kobayashi, Nana Imai, Toshihiko Tamura, Susumu Nishihara, Yukihisa Nishizawa, Akihiro Tagaya, Yasuhiro Koike, and Yoshi Okamoto

Appl. Phys. Lett. 77, 331 (2000); http://dx.doi.org/10.1063/1.126967 (3 pages) | Cited 15 times

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A graded-index polymer optical fiber containing rhodamine 6G in poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) has been fabricated. Lasing behavior of the fiber was observed by pumping with a frequency-doubled Q-switched Nd: yttrium–aluminum–garnet laser. A slope efficiency of 43% and a lifetime of 110 000 shots at a repetition rate of 10 Hz have been observed. With a 1.5 mJ pump energy, an output energy of 640 μJ was produced. © 2000 American Institute of Physics.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.55.Mv Dye lasers
42.81.Ht Gradient-index (GRIN) fiber devices

Intersubband absorption in GaN/AlGaN multiple quantum wells in the wavelength range of λ ∼ 1.75–4.2 μm

Claire Gmachl, Hock M. Ng, and Alfred Y. Cho

Appl. Phys. Lett. 77, 334 (2000); http://dx.doi.org/10.1063/1.126968 (3 pages) | Cited 5 times

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Intersubband optical absorption in narrow, 15–30 Å wide, GaN/AlGaN quantum wells has been measured. The samples were grown by molecular-beam epitaxy on sapphire substrate and the barrier AlN mole fraction was varied from 0.45 to 0.8. Peak absorption wavelengths ranged from 4.2 μm for 30 Å wide wells to 1.77 μm for a 15 Å wide well. Modeling shows that a large contribution to the considerable spectral width of the absorption of ∼150 meV likely results from monolayer fluctuations. In addition to the composition dependent band offset, the intrinsic electric fields in the wells and barriers are the determining factors for the shortest possible wavelength. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Low-noise and high-gain image amplification by contradirectional two-wave mixing

Xiaodong Mu, Xinguang Xu, Zongshu Shao, Minhua Jiang, and Haosu Luo

Appl. Phys. Lett. 77, 337 (2000); http://dx.doi.org/10.1063/1.126969 (3 pages)

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Contradirectional two-wave mixing (CTWM) is demonstrated to be a perfect configuration for low-noise and high-gain image amplification. Compared with the image amplified by the forward two-wave mixing configuration, the signal-to-noise ratio is increased from 6 to 2×104 in the experiments in Rh-doped BaTiO3 crystal. The gain of the signal beam is also enhanced effectively. We have contrasted the differences between the two experimental configurations and gave a credible explanation for the low noise and high gain that exists in the CTWM configuration. © 2000 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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