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6 Mar 2000

Volume 76, Issue 10, pp. 1219-1345

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1.6 W continuous-wave coherent power from large-index-step (Δn ≈ 0.1) near-resonant, antiguided diode laser arrays

H. Yang, L. J. Mawst, and D. Botez

Appl. Phys. Lett. 76, 1219 (2000); http://dx.doi.org/10.1063/1.125990 (3 pages) | Cited 11 times

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Near-diffraction-limited-beam continuous-wave (cw) operation has been achieved to high powers from antiguided arrays with a large effective-index step between element and interelement regions. InGaAs/InGa(As)P/GaAs 40-element arrays (λ = 0.985 μm) emit in beams 2×diffraction-limit (0.67°) at 1.6 W and 9×threshold in cw operation. 1 W of the coherent cw power resides in the central lobe. The external differential quantum efficiency and the threshold current are 40% and 0.4 A, respectively, for 1-mm-long devices of 191 μm emitting aperture. The overall electrical to optical power conversion efficiency at 1.6 W output power is 23%. Modeling of the thermal effects in cw operation on the array modes reveals that for high-index-step (∼0.1) near-resonant antiguided arrays thermal lensing hardly affects high-order modes, and as a consequence, 2×diffraction-limited beams can be maintained to watt-range cw powers. © 2000 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Dynamic response of 1.3-μm-wavelength InGaAs/GaAs quantum dots

L. Zhang, Thomas F. Boggess, D. G. Deppe, D. L. Huffaker, O. B. Shchekin, and C. Cao

Appl. Phys. Lett. 76, 1222 (2000); http://dx.doi.org/10.1063/1.125991 (3 pages) | Cited 40 times

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The temperature-dependent dynamic response of 1.3-μm-InGaAs/GaAs quantum dots is investigated using time-resolved photoluminescence upconversion with subpicosecond temporal resolution for excitation in either the GaAs bulk region surrounding the dots or within the wetting layer. Relaxation to the quantum-dot ground state occurs on a time scale as short as 1 ps, while radiative lifetimes as short as 400 ps are measured. The influence of nonradiative recombination is observed only for temperatures above 250 K. At temperatures below 77 K, an increase in the relaxation time and lifetime is observed when carriers are injected into the bulk GaAs region versus excitation into the wetting layer, which suggests that diffusion in the bulk GaAs region influences both the relaxation rate and the recombination rate. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics

Continuous wave simultaneous multi-self-frequency conversion in Nd3+-doped aperiodically poled bulk lithium niobate

J. Capmany, V. Bermúdez, D. Callejo, J. García Solé, and E. Diéguez

Appl. Phys. Lett. 76, 1225 (2000); http://dx.doi.org/10.1063/1.125897 (3 pages) | Cited 11 times

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We report simultaneous participation of the fundamental laser wave in self-frequency doubling and self-sum-frequency mixing with pump radiation in Nd3+-doped bulk aperiodically poled lithium niobate structures. A green continuous wave visible laser output power of 1.5 mW generated by self-frequency doubling and 0.5 mW of blue generated by self-sum-frequency mixing have been obtained simultaneously from 30 mW of laser output power available in the fundamental. Stable and efficient infrared laser action at room temperature is obtained in both 4F3/2→4I11/2 and 4F3/2→4I13/2 laser channels of Nd3+ ion without oxide codoping, although some residual photorefractive damage for the visible outputs is observed. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.By Design of specific laser systems

Photoinduced layer alignment control in ferroelectric liquid crystal with N∗–C∗ phase transition doped with photochromic dye

Tatsunosuke Matsui, Keizo Nakayama, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 76, 1228 (2000); http://dx.doi.org/10.1063/1.125992 (3 pages) | Cited 7 times

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Photoinduced layer alignment control has been proposed in an azo-dye-doped ferroelectric liquid crystal with a chiral nematic (N∗)–chiral smectic C (SmC∗) phase sequence. This layer alignment control is based on the N∗–SmC∗ phase transition induced by the photoisomerization of the azo-dye. Trans-cis photoisomerization of the azo-dye upon UV irradiation in the SmC∗ phase induces the N∗ phase, and an opposite isomerization process upon sequentially stopping the UV irradiation induces the SmC∗ phase again. The photoinduced SmC∗–N∗–SmC∗ phase transition under an appropriate electric field allows us to control the smectic layer alignment. This photoassisted layer switching can be applied to the fabrication of the designed multidomain structure in electro-optic elements such as display, optical memory, and optical grating. © 2000 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
82.30.Qt Isomerization and rearrangement
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
78.20.Jq Electro-optical effects

Efficient high-speed near-infrared Ge photodetectors integrated on Si substrates

L. Colace, G. Masini, G. Assanto, Hsin-Chiao Luan, K. Wada, and L. C. Kimerling

Appl. Phys. Lett. 76, 1231 (2000); http://dx.doi.org/10.1063/1.125993 (3 pages) | Cited 68 times

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We have fabricated Ge/Si heterojunction photodetectors with high responsivities of 550 mA/W at 1.32 μm and 250 mA/W at 1.55 μm and time responses shorter than 850 ps. High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition followed by cyclic thermal annealing. The beneficial effect of the post-growth thermal annealing on the electrical properties of Ge epilayers, due to the reduction of threading-dislocation densities, is confirmed by the dramatic enhancement of the performance of the photodetectors. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.Cc Kinetics of defect formation and annealing
73.61.Cw Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm

J. Alnis, U. Gustafsson, G. Somesfalean, and S. Svanberg

Appl. Phys. Lett. 76, 1234 (2000); http://dx.doi.org/10.1063/1.125994 (3 pages) | Cited 16 times

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Blue diode lasers emitting 5 mW continuous-wave power around 400 nm have recently become available. We report on the use of a blue diode laser together with a 30 mW red diode laser for sum-frequency generation around 254 nm. The ultraviolet power is estimated to be 0.9 nW, and 35 GHz mode-hop-free tuning range is achieved. This is enough to perform high-resolution ultraviolet spectroscopy of mercury isotopes. The possibility to use frequency modulation in the ultraviolet is demonstrated; however, at present the ultraviolet power is too low to give advantages over direct absorption monitoring. Mercury detection at atmospheric pressure is also considered which is of great interest for environmental monitoring. © 2000 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.62.Fi Laser spectroscopy
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.88.+y Instruments for environmental pollution measurements

Molecular orientation in laser-induced periodic microstructure on polyimide surface

Qing-hua Lu, Zong-guang Wang, Jie Yin, Zi-kang Zhu, and H. Hiraoka

Appl. Phys. Lett. 76, 1237 (2000); http://dx.doi.org/10.1063/1.125995 (3 pages) | Cited 8 times

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The dichroism of the laser-induced periodic microstructure on a polyimide surface was studied with polarized reflectance infrared spectroscopy. The experimental results show that the polar C�O groups in the polyimide exhibit a greater tendency of orienting in the direction parallel to the microlines while the nonpolar C–C–C linkages between the two benzene rings in the diamine moiety tend to orient in a direction perpendicular to the nanolines. This result indicates that the polyimide molecule chains tend to orient in a direction perpendicular to the nanolines. © 2000 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.20.Fm Birefringence
78.30.Jw Organic compounds, polymers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Ultrahigh-resolution liquid crystal display with gray scale

Bing Wen, Milind P. Mahajan, and Charles Rosenblatt

Appl. Phys. Lett. 76, 1240 (2000); http://dx.doi.org/10.1063/1.125996 (3 pages) | Cited 38 times

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An atomic force microscope was used to write planar alignment patterns on a polyimide-coated glass substrate. Paired with a substrate treated for homeotropic alignment, the resulting hybrid liquid crystal cell produced fixed gray scale images with pixel sizes of order 1 μm. The physics and efficacy of this architecture are compared to a cell having planar alignment at both substrates. © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.30.Va Image forming and processing
07.79.Lh Atomic force microscopes

Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium

Takashi Yamasaki, Kazuhiro Sumioka, and Tetsuo Tsutsui

Appl. Phys. Lett. 76, 1243 (2000); http://dx.doi.org/10.1063/1.125997 (3 pages) | Cited 90 times

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Periodic dielectric structures, consisting of hexagonally closed-packed arrays of silica microspheres with the diameter of 550 nm, were incorporated into organic light-emitting devices with a conventional two-layer structure made with vacuum-sublimation. The arrays acted as a two-dimensional diffraction lattice which behaved as a light scattering medium for the light propagated in waveguiding modes within the device. Strongly scattered light emission through the front surface of the devices was observed. An increase in the device coupling-out factor for electroluminescent efficiency by using the scattering structure is demonstrated. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
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