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10 Jul 2006

Volume 89, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 023901 (2006); http://dx.doi.org/10.1063/1.2219984 (3 pages)

Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham
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Coupled-wave model for square-lattice two-dimensional photonic crystal with transverse-electric-like mode

Kyosuke Sakai, Eiji Miyai, and Susumu Noda

Appl. Phys. Lett. 89, 021101 (2006); http://dx.doi.org/10.1063/1.2220057 (3 pages) | Cited 10 times

Online Publication Date: 11 July 2006

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We propose a coupled-wave model for a square-lattice two-dimensional (2D) photonic crystal (PC) with a transverse electric mode. A set of coupled-wave equations is obtained from this model and it is shown that 2D optical coupling occurs between four light waves propagating in the Γ-X direction via higher-order waves propagating in the Γ-M direction. The expressions for the resonant mode frequencies derived from the coupled-wave equations describe the characteristics of experimental results for the band-edge frequencies of the 2D PC laser.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials

Photonic crystal waveguide switch with a microelectromechanical actuator

Ken-ichi Umemori, Yoshiaki Kanamori, and Kazuhiro Hane

Appl. Phys. Lett. 89, 021102 (2006); http://dx.doi.org/10.1063/1.2219996 (3 pages) | Cited 16 times

Online Publication Date: 11 July 2006

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A photonic crystal waveguide switch with a movable slab is proposed and fabricated by silicon micromachining. The switch structure consists of in-line input and output photonic crystal waveguide slabs and a switching slab to bridge gap between the waveguides. Driving the switching slab with a microelectromechanical actuator, the transmission between the waveguides is modulated. The switching characteristics can be explained by calculations using the finite-difference time-domain method.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.Gw Other integrated-optical elements and systems
42.79.Gn Optical waveguides and couplers
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Polarization-independent and submillisecond response phase modulators using a 90° twisted dual-frequency liquid crystal

Yuhua Huang, Chien-Hui Wen, and Shin-Tson Wu

Appl. Phys. Lett. 89, 021103 (2006); http://dx.doi.org/10.1063/1.2219998 (3 pages) | Cited 15 times

Online Publication Date: 11 July 2006

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A polarization-independent phase modulator using a 90° twisted dual-frequency liquid crystal (DFLC) is demonstrated. In addition to being polarization independent, such a phase modulator exhibits many other advantages such as being scattering-free and having large phase change, low operating voltage, and submillisecond response time. Using a 15 μm transmissive DFLC cell, the phase shift achieves 1π at λ = 633 nm and the applied voltage is lower than 25 Vrms. Potential applications of such a phase modulator for laser beam steering, tunable-focus lenses, and switchable two-dimensional/three-dimensional liquid crystal displays are foreseeable.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
42.79.Hp Optical processors, correlators, and modulators
61.30.-v Liquid crystals

Semiconductor waveguide optical isolator based on nonreciprocal loss induced by ferromagnetic MnAs

T. Amemiya, H. Shimizu, Y. Nakano, P. N. Hai, M. Yokoyama, and M. Tanaka

Appl. Phys. Lett. 89, 021104 (2006); http://dx.doi.org/10.1063/1.2220016 (3 pages) | Cited 17 times

Online Publication Date: 11 July 2006

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We fabricated TM mode InGaAlAs/InP active waveguide optical isolators based on the magnetically induced nonreciprocal loss. We used epitaxially grown MnAs thin films as ferromagnetic electrodes of the semiconductor active waveguide optical isolators. We demonstrated TM mode nonreciprocal propagation (8.8 dB/mm) at 1540 nm with an excellent ferromagnetic electrode contact, which has greater semiconductor active waveguide optical isolator performance than that of our previously reported devices with Ni/Fe polycrystalline electrodes.
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42.79.Gn Optical waveguides and couplers
85.70.Sq Magnetooptical devices
78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys

Generation of white light from optically pumped gallium nitride epilayers

Faiz Rahman and Nigel P. Johnson

Appl. Phys. Lett. 89, 021105 (2006); http://dx.doi.org/10.1063/1.2219149 (3 pages)

Online Publication Date: 11 July 2006

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We describe results of optical pumping experiments on gallium nitride (GaN) epilayers grown on sapphire and capped with a layer of aluminum gallium nitride (AlGaN). Our samples show the well-known yellow luminescence (in response to exposure with ultraviolet radiation) that derives from transitions to and from defect-induced gap states. We show that it is possible to enhance this downconversion luminescence by subjecting samples to mechanical stress through ultrasonic wave propagation. When double pumped with both ultraviolet and visible blue radiations, the samples generate broadband visible radiation that appears white to the human eye.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Space-selective laser joining of dissimilar transparent materials using femtosecond laser pulses

Wataru Watanabe, Satoshi Onda, Takayuki Tamaki, Kazuyoshi Itoh, and Junji Nishii

Appl. Phys. Lett. 89, 021106 (2006); http://dx.doi.org/10.1063/1.2221393 (3 pages) | Cited 18 times

Online Publication Date: 11 July 2006

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We report on the joining of dissimilar transparent materials based on localized melting and resolidification of the materials only around the focal volume due to nonlinear absorption of focused femtosecond laser pulses. We demonstrate the joining of borosilicate glass and fused silica, whose coefficients of thermal expansion are different. The joint strength and the transmittance through joint volume were investigated by varying the translation velocity of the sample and the pulse energy of the irradiated laser pulses.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.70.D- Solid-liquid transitions
81.30.Fb Solidification
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Gain saturation and high-power pulsed operation of GaSb-based tapered diode lasers with separately contacted ridge and tapered section

C. Pfahler, M. Eichhorn, M. T. Kelemen, G. Kaufel, M. Mikulla, J. Schmitz, and J. Wagner

Appl. Phys. Lett. 89, 021107 (2006); http://dx.doi.org/10.1063/1.2218823 (3 pages) | Cited 1 time

Online Publication Date: 12 July 2006

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(AlGaIn)(AsSb) ridge-waveguide tapered diode lasers with separately contacted ridge and tapered sections, emitting at 1.93 μm, have been analyzed in pulsed mode with respect to their high-power capability and wavelength tunability. Operating the ridge section above saturation, a variation of the current through this section resulted in a change in lasing wavelength, while changing the current injected into the tapered section at a constant ridge current allowed to vary the output power at constant lasing wavelength. Furthermore, the optical power required to saturate the tapered amplifier section has been derived from a comparison of the experimental characteristics with beam propagation method calculations.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.-k Nonlinear optics
42.60.Fc Modulation, tuning, and mode locking

Frequency tunability of the terahertz silicon laser by a magnetic field

S. G. Pavlov, H.-W. Hübers, M. F. Kimmitt, H. Riemann, and V. N. Shastin

Appl. Phys. Lett. 89, 021108 (2006); http://dx.doi.org/10.1063/1.2220551 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2006

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By applying a magnetic field to the terahertz intracenter silicon laser the degeneracy of the donor states is lifted. In the case of a bismuth doped silicon laser operating at 6 THz it is demonstrated that this effect can be used to tune the emission frequency. The frequency change depends on the relative orientation of the magnetic field and the crystallographic axis of the laser. The tuning rate is 40–60 GHz/T. The frequency tunability is explained by the linear Zeeman effect which splits the 2p± donor state acting as the upper laser level in the Si:Bi laser.
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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

Subnanosecond piezoelectric x-ray switch

Alexei Grigoriev, Dal-Hyun Do, Dong Min Kim, Chang-Beom Eom, Paul G. Evans, Bernhard Adams, and Eric M. Dufresne

Appl. Phys. Lett. 89, 021109 (2006); http://dx.doi.org/10.1063/1.2219342 (3 pages) | Cited 11 times

Online Publication Date: 12 July 2006

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We report an ultrafast piezoelectric switch for synchrotron x rays. A thin epitaxial film of piezoelectric Pb(Zr,Ti)O3 works as a diffractive optical switch at frequencies from dc to >1 GHz. The broad frequency range allows single bunches of synchrotron x rays to be selected in an arbitrary sequence. The piezoelectric effect introduces mechanical strains of a fraction of 1% in the Pb(Zr,Ti)O3 film, which can be used for blocking or passing diffracted x rays.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
41.50.+h X-ray beams and x-ray optics
07.85.Qe Synchrotron radiation instrumentation

Simultaneous formation of visible and ultraviolet random lasings in ZnO films

H. D. Li, S. F. Yu, S. P. Lau, and Eunice S. P. Leong

Appl. Phys. Lett. 89, 021110 (2006); http://dx.doi.org/10.1063/1.2221406 (3 pages) | Cited 23 times

Online Publication Date: 12 July 2006

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We have demonstrated visible and ultraviolet random laser actions simultaneously from highly disordered ZnO polycrystalline thin films under optical excitation. It is found that the realization of ZnO grain boundaries by thermal annealing can provide sufficient optical gain (i.e., related to deep-defect-level radiative recombination) and coherent feedback to achieve random laser action at visible wavelength. Furthermore, the coexistence of visible and ultraviolet random lasings inside the highly disordered ZnO films is due to the size difference of the random cavities at different wavelengths.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Thermal properties of THz quantum cascade lasers based on different optical waveguide configurations

Miriam S. Vitiello, Gaetano Scamarcio, Vincenzo Spagnolo, Jesse Alton, Stefano Barbieri, Chris Worrall, Harvey E. Beere, David A. Ritchie, and Carlo Sirtori

Appl. Phys. Lett. 89, 021111 (2006); http://dx.doi.org/10.1063/1.2220546 (3 pages) | Cited 18 times

Online Publication Date: 13 July 2006

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We compare the thermal properties of THz quantum cascade lasers (QCLs) fabricated with metal-metal optical waveguides based on Au/Au or In/Au wafer bonding. This information was obtained from the analysis of microprobe band-to-band photoluminescence spectra measured on devices operating in continuous wave (cw). The experimental normalized thermal resistances (RL*), show that the use of Au/Au wafer bonding optimizes the heat dissipation. Comparison with surface-plasmon based THz QCLs, demonstrates that the use of metal-metal wafer bonding can allow cw operation at progressively higher temperatures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

ZnO homojunctions grown by cosputtering ZnO and Zn3P2 targets

Guangxia Hu, Hao Gong, E. F. Chor, and Ping Wu

Appl. Phys. Lett. 89, 021112 (2006); http://dx.doi.org/10.1063/1.2221399 (3 pages) | Cited 5 times

Online Publication Date: 13 July 2006

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We have demonstrated the growth and control of the conductivity type (n or p) of ZnO doped with phosphorus (P). The success of p-type and n-type P-doped ZnO is confirmed by Hall effect measurements, Seebeck measurements, and the realization of p-n homojunctions. The room temperature carrier concentration, mobility, and resistivity of the as-deposited p-type P-doped ZnO are 2.8×1017 cm−3, 0.341 cm2/V s, and 65.4 Ω cm, respectively. The P-doped ZnO p-n homojunctions have a turn-on voltage of about 3.4 V. Photoluminescence spectra show that the P-doped films may have a shallow accepter energy level.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
78.55.Et II-VI semiconductors

Storage-ring-based, ultrashort positron beam source

Yuelin Li, Weiming Guo, Katherine Harkay, and Wanming Liu

Appl. Phys. Lett. 89, 021113 (2006); http://dx.doi.org/10.1063/1.2221503 (3 pages) | Cited 1 time

Online Publication Date: 13 July 2006

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We propose a scheme to generate high-flux, short-burst γ-ray radiation and its application for generating ultrashort positron beams. The intense γ-ray bursts are generated from short laser pulses scattering off high-energy electron beams in a storage ring. The γ-ray bursts are then used to irradiate thin metal targets to generate the positron beams via pair production. Using the example of the Advanced Photon Source storage ring, more than 107 positrons/s in 1 ps pulses at energies of a few MeV can be generated.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.77.Ka Charged-particle beam sources and detectors
29.25.Bx Electron sources
29.20.db Storage rings and colliders
41.75.Fr Electron and positron beams

Strong broad C-band room-temperature photoluminescence in amorphous Er2O3 film

A. M. Grishin, E. V. Vanin, O. V. Tarasenko, S. I. Khartsev, and P. Johansson

Appl. Phys. Lett. 89, 021114 (2006); http://dx.doi.org/10.1063/1.2221517 (3 pages) | Cited 11 times

Online Publication Date: 13 July 2006

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Photoluminescence with the bandwidth of 45 nm (1523–1568 nm at the level of 3 dB) was observed in amorphous Er2O3 films grown on quartz substrate by pulsed laser ablation of erbium oxide stoichiometric target. Optical transmission spectrum has been fitted to Swanepoel formula [ J. Phys. E 16, 1214 (1983) ] to determine dispersion of refractive index and to extract resonance absorption peaks at 980 and 1535 nm. The maximum gain coefficient as high as 800 dB/cm at 1535 nm was estimated using McCumber theory and experimental spectrum of the resonance absorption. For 5 mm long waveguide amplifier with erbium doping confinement factor of 0.1, the theory predicts the spectral gain of 18 dB with 1.2 dB peak-to-peak flatness in the bandwidth of 31 nm (1532–1563 nm) when 73% of Er3+ ions are excited from the ground state to the math laser level. Strong broadband photoluminescence at room temperature and inherently flat spectral gain promise Er2O3 films for ultrashort high-gain optical waveguide amplifiers and integrated light circuits.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Wc Optical coatings

How many O2(math) molecules are consumed per dissociated I2 in chemical oxygen-iodine lasers?

V. Rybalkin, A. Katz, K. Waichman, D. Vingurt, Z. Dahan, B. D. Barmashenko, and S. Rosenwaks

Appl. Phys. Lett. 89, 021115 (2006); http://dx.doi.org/10.1063/1.2221903 (3 pages) | Cited 8 times

Online Publication Date: 14 July 2006

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Direct measurements of the dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) as a function of I2 flow rate were carried out. This enabled us to determine the number of consumed O2(math) molecules per dissociated I2 molecule. The number depends on the experimental conditions: it is 4.2±0.4 for typical conditions and I2 densities applied for the operation of the COIL, but increases at lower I2 densities. Possible dissociation mechanisms consistent with our results are discussed and the importance of dissociating I2 prior to its mixing with O2(math) is stressed.
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42.55.Ks Chemical lasers
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
33.80.Gj Diffuse spectra; predissociation, photodissociation

Photoaddressable bistable reflective liquid crystal display

Tsung-Hsien Lin, Hung-Chang Jau, San-Yi Hung, Huei-Ru Fuh, and Andy Y.-G. Fuh

Appl. Phys. Lett. 89, 021116 (2006); http://dx.doi.org/10.1063/1.2219406 (3 pages) | Cited 11 times

Online Publication Date: 14 July 2006

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This work presents a bistable reflective liquid crystal display. The mechanism is based on the laser-induced adsorption of azo dyes on the polymer-coated glass substrate. This reflective liquid crystal display is very simple to fabricate and can be optically written, erased, and rewritten with a high contrast. A simulation is performed to fit the measured electro-optical characteristics of this device.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
42.65.Pc Optical bistability, multistability, and switching, including local field effects
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