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15 Sep 2003

Volume 83, Issue 11, pp. 2091-2291

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 2244 (2003); http://dx.doi.org/10.1063/1.1610259 (3 pages)

X.-M. Meng, Y. Jiang, J. Liu, C.-S. Lee, I. Bello, and S.-T. Lee
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Submicron diamond-lattice photonic crystals produced by two-photon laser nanofabrication

Koshiro Kaneko, Hong-Bo Sun, Xuan-Ming Duan, and Satoshi Kawata

Appl. Phys. Lett. 83, 2091 (2003); http://dx.doi.org/10.1063/1.1610253 (3 pages) | Cited 41 times

Online Publication Date: 9 September 2003

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Diamond-lattice photonic crystal structures consisting of around 500-nm-diameter 〈111〉 rods and 580-nm-diameter photonic atoms were realized by two-photon photopolymerization. In the course of laser nanofabrication, it was found that the surface quality of elements depended on the crystal geometry, which was then interpreted as voxel floating effect arising from insufficient overlapping degree of voxels. With the solution of this issue, nearly perfect photonic lattices were obtained, from which single-period power rejection of approximately 35% was achieved. This work is an important step toward arbitrarily tailoring the density of photon states of photonic crystals according to end use by engineering cavity or crystalline geometry. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

Enhanced blue emission from Tm-doped AlxGa1−xN electroluminescent thin films

D. S. Lee and A. J. Steckl

Appl. Phys. Lett. 83, 2094 (2003); http://dx.doi.org/10.1063/1.1611275 (3 pages) | Cited 22 times

Online Publication Date: 9 September 2003

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Electroluminescent (EL) emission from Tm-doped AlxGa1−xN (AlxGa1−xN:Tm) has been observed with various Al compositions (0 ⩽ x ⩽ 1). AlxGa1−xN:Tm thin films were grown by molecular beam epitaxy with in situ doping of Tm. At lower Al composition (x<0.15), blue emission at 478 nm dominates, corresponding to the Tm 1G4→3H6 transition. For x>0.15, however, a second blue emission peak was observed at 465 nm, becoming dominant with increasing Al composition. The 465 nm emission is attributed to the higher level Tm transition 1D2→3F4, which was not observed in GaN:Tm. Blue EL emission from Tm was enhanced with Al content in the films. The ratio of EL intensity at blue (465 nm plus 478 nm) to infrared (801 nm) wavelengths increased monotonically with Al composition, from ∼2 for GaN:Tm to ∼30 for AlN:Tm. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ultraviolet light selective photodiode based on an organic–inorganic heterostructure

J. Yamaura, Y. Muraoka, T. Yamauchi, T. Muramatsu, and Z. Hiroi

Appl. Phys. Lett. 83, 2097 (2003); http://dx.doi.org/10.1063/1.1610793 (3 pages) | Cited 13 times

Online Publication Date: 9 September 2003

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We show a perfect ultraviolet (UV) light selective and sensitive photovoltaic cell easily fabricated. The device consists of a water-soluble p-type semiconducting polymer PEDOT-PSS: poly(3,4-ethylenedioxythiophene) doped by poly(4-styrenesulfonate) film deposited on a Nb-doped titanium oxide (SrTiO3:Nb) substrate. For the PEDOT-PSS/SrTiO3:Nb heterostructure, the photosensitivity at zero bias for the UV light with L = 1 mW/cm2 is estimated to be 0.05 A/W, corresponding to a quantum yield of 16% electron/photon. This device is only activated in the UV region (λ<390 nm), and then, it exhibits a large response to the UV–B light (290–320 nm). © 2003 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Distribution of density of photonic states in amorphous photonic materials

Yiquan Wang, Bingying Cheng, and Daozhong Zhang

Appl. Phys. Lett. 83, 2100 (2003); http://dx.doi.org/10.1063/1.1609663 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2003

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The density of states (DOS) and local density of states (LDOS) for an amorphous photonic material (APM) with a finite size and constructed by hexagonal basic cells are simulated. It is found that there is a frequency interval in which the total DOS is very small, i.e., a photonic gap exists. Near the gap-center frequency, the LDOS drops rapidly from the edge to the center area of the sample. However, at the gap-edge frequency, some discrete spots with high LDOS spread in the sample and corresponding electric field distributions show the occurrence of localized modes. This phenomenon can be attributed to the disordered distribution of the scatterers. © 2003 American Institute of Physics.
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71.23.An Theories and models; localized states
42.70.Qs Photonic bandgap materials
71.55.Jv Disordered structures; amorphous and glassy solids
78.20.-e Optical properties of bulk materials and thin films

Simultaneous production of spin-polarized ions/electrons based on two-photon ionization of laser-ablated metallic atoms

Takashi Nakajima, Nobuaki Yonekura, Yukari Matsuo, Tohru Kobayashi, and Yoshimitsu Fukuyama

Appl. Phys. Lett. 83, 2103 (2003); http://dx.doi.org/10.1063/1.1610800 (3 pages) | Cited 10 times

Online Publication Date: 9 September 2003

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We demonstrate the simultaneous production of spin-polarized ions/electrons using two-color, two-photon ionization of laser-ablated metallic atoms. Specifically, we have applied the developed technique to laser-ablated Sr atoms, and found that the electron-spin polarization of Sr+ ions, and accordingly, the spin polarization of photoelectrons is 64%±9%, which is in good agreement with the theoretical prediction we have recently reported [T. Nakajima and N. Yonekura, J. Chem. Phys. 117, 2112 (2002)]. Our experimental results open up a simple way toward the construction of a spin-polarized dual ion/electron source. © 2003 American Institute of Physics.
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32.80.Fb Photoionization of atoms and ions
32.80.Rm Multiphoton ionization and excitation to highly excited states

Infrared passbands from fractal slit patterns on a metal plate

Weijia Wen, Z. Yang, Gu Xu, Yonghai Chen, Lei Zhou, Weikun Ge, C. T. Chan, and Ping Sheng

Appl. Phys. Lett. 83, 2106 (2003); http://dx.doi.org/10.1063/1.1611271 (3 pages) | Cited 15 times

Online Publication Date: 9 September 2003

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We show that a fractal pattern of submicron wide slits, etched on a 0.1-μm-thick gold film, exhibit multiple pass and stop bands in the wavelength regime of 2–200 μm. In the midinfrared regime, the passbands show ∼ 36% transmission (three orders of magnitude higher than the reference), and the stop bands exhibit ∼ 80% reflection. In the far infrared regime, the passband transmittances are 25%, 29%, and 14%, respectively, at wavelengths of 34, 62, and 111 μm. These transmittances are rather high in view of the fact that supporting substrate is itself only about 40% transmitting, and a control pattern of holes with similar void-to-metal ratio is 3000 times less transmitting in all frequencies. We attribute the high transmittance from subwavelength slits to geometric resonances. © 2003 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
78.30.Er Solid metals and alloys
05.45.Df Fractals
42.79.Ci Filters, zone plates, and polarizers

Room-temperature type-II interband cascade lasers near 4.1 μm

Rui Q. Yang, Cory J. Hill, Baohua Yang, and John K. Liu

Appl. Phys. Lett. 83, 2109 (2003); http://dx.doi.org/10.1063/1.1611260 (3 pages) | Cited 15 times

Online Publication Date: 9 September 2003

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Operation of type-II interband cascade lasers has been demonstrated in pulsed mode at room temperatures at wavelengths near 4.1 μm. These lasers fabricated with 150 μm wide mesa stripes also operated in cw mode at temperatures up to 145 K. Threshold current densities as low as 9 A/cm2 and output powers exceeding 100 mW/f have been achieved in cw mode at 80 K. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Experimental evidence of carrier leakage in InGaAsN quantum-well lasers

Nelson Tansu, Jeng-Ya Yeh, and Luke J. Mawst

Appl. Phys. Lett. 83, 2112 (2003); http://dx.doi.org/10.1063/1.1611279 (3 pages) | Cited 28 times

Online Publication Date: 9 September 2003

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Carrier leakage processes are shown experimentally as one of the factors contributing to the temperature sensitivity of InGaAsN quantum well lasers. The utilization of the direct barriers of GaAs0.85P0.15 instead of GaAs, surrounding the InGaAsN quantum-well (QW)-active region, leads to significant suppression of carrier leakage at elevated temperatures of 90–100 °C. Threshold current densities of only 390 and 440 A/cm2 was achieved for InGaAsN QW lasers (Lcav = 2000 μm) with GaAs0.85P0.15-direct barriers at temperature of 80 and 90 °C, respectively. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Ultrafast nonresonant third-order optical nonlinearity of fullerene-containing polyurethane films at telecommunication wavelengths

Qiying Chen, Li Kuang, Edward H. Sargent, and Zhi Yuan Wang

Appl. Phys. Lett. 83, 2115 (2003); http://dx.doi.org/10.1063/1.1609660 (3 pages) | Cited 30 times

Online Publication Date: 9 September 2003

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High-optical-quality polyurethane films containing a high load of (60)fullerene (C60) were prepared by reaction of the hydroxy-containing C60 and triisocyanate with the goal of obtaining enhanced nonresonant third-order optical nonlinearity. Optical nonlinearity was measured using the Z-scan technique in the wavelength range 1150–1600 nm. This revealed a positive Kerr coefficient with nonresonant n2 equal to 2.0(±0.6)×10−3 cm2/GW and excellent linear-absorption and nonlinear-absorption figures of merit at 1550 nm. The technique reported herein is a new approach to obtain fullerene films with the capacity to realize a high number density of C60 moieties. These resulted in more than 2 orders of enhancement in the third-order susceptibility over recently reported C60 sol and gel, and an enlarged second-order hyperpolarizability resulting from further enhanced charge transfer processes. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Bs Wave propagation, transmission and absorption
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Blue, surface-emitting, distributed feedback polyfluorene lasers

G. Heliotis, R. Xia, D. D. C. Bradley, G. A. Turnbull, I. D. W. Samuel, P. Andrew, and W. L. Barnes

Appl. Phys. Lett. 83, 2118 (2003); http://dx.doi.org/10.1063/1.1612903 (3 pages) | Cited 51 times

Online Publication Date: 9 September 2003

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We report the fabrication of optically-pumped solid-state distributed feedback lasers utilizing two blue-light-emitting semiconducting polyfluorenes as gain media. The lasers were readily fabricated by solution deposition of thin polymer films on top of gratings etched into fused silica substrates. A compact Nd:YVO4 microchip laser was used as the pump source for the two polymers studied, and lasing was achieved at 455 and 465 nm. Low threshold energies, ⩾4 nJ per pulse, were obtained. The emission characteristics of the lasers are described along with the results of additional experiments that investigate in more detail the effect of the grating microstructure on polymer light emission. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.70.Jk Polymers and organics

Room-temperature GaN vertical-cavity surface-emitting laser operation in an extended cavity scheme

Si-Hyun Park, Jaehoon Kim, Heonsu Jeon, Tan Sakong, Sung-Nam Lee, Suhee Chae, Y. Park, Chang-Hyun Jeong, Geun-Young Yeom, and Yong-Hoon Cho

Appl. Phys. Lett. 83, 2121 (2003); http://dx.doi.org/10.1063/1.1611643 (3 pages) | Cited 42 times

Online Publication Date: 9 September 2003

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A GaN-based vertical-cavity surface-emitting laser (VCSEL) has been demonstrated in an extended cavity structure. A VCSEL device had a long extended cavity, which consisted of a sapphire substrate as well as a GaN epilayer and had an integrated microlens on one side. High-reflection dielectric mirrors were deposited on both sides of the laser cavity. The laser was optically pumped and operated at room temperature. The VCSEL device lased at a low threshold excitation intensity of 160 kW/cm2. In contrast to a conventional microcavity-VCSEL structure, the VCSEL operated in multiple longitudinal modes with mode spacing consistent with its physical thickness. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz quantum-cascade laser at λ ≈ 100 μm using metal waveguide for mode confinement

Benjamin S. Williams, Sushil Kumar, Hans Callebaut, Qing Hu, and John L. Reno

Appl. Phys. Lett. 83, 2124 (2003); http://dx.doi.org/10.1063/1.1611642 (3 pages) | Cited 91 times

Online Publication Date: 9 September 2003

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We report lasing at ∼ 3.0 THz (λ ≈ 98–102 μm) in a quantum-cascade structure in which mode confinement is provided by a double-sided metal waveguide. The depopulation mechanism is based on resonant phonon scattering, as in our previous work. Lasing takes place in pulsed mode up to a heat-sink temperature of 77 K. The waveguide consists of metallic films placed above and below the 10-μm-thick multiple-quantum-well gain region, which gives low losses and a modal confinement factor of nearly unity. Fabrication takes place via low-temperature metallic wafer bonding and subsequent substrate removal using selective etching. This type of waveguide is expected to be increasingly advantageous at even longer wavelengths. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
42.50.Pq Cavity quantum electrodynamics; micromasers
42.82.-m Integrated optics
42.79.Gn Optical waveguides and couplers

Subfemtosecond pulse generation by nonadiabatic molecular modulation

Jian Wu and Heping Zeng

Appl. Phys. Lett. 83, 2127 (2003); http://dx.doi.org/10.1063/1.1611646 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2003

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We suggest a technique to generate subfemtosecond pulse train in a Raman generator driven by three sufficiently intense single-mode laser beams whose carrier frequencies are tuned off the Raman resonance with two different two-photon detunings. The Raman interaction establishes a molecular modulation through a nonadiabatic process. The simulation based on the first fundamental vibrational Raman transition of solid hydrogen indicates that subfemtosecond pulse train can be generated when the signs of the two-photon detunings are opposite. This opens an experimentally feasible way to observe enhanced generation of broadband Raman sidebands as well as compression of the phase-locked Raman sidebands into subfemtosecond pulse trains in the same Raman media with above- and below-resonance Raman excitations. © 2003 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Giant dielectric permittivity and electromechanical strain in thin film materials produced by pulsed-laser deposition

I. Vrejoiu, J. D. Pedarnig, D. Bäuerle, and M. Dinescu

Appl. Phys. Lett. 83, 2130 (2003); http://dx.doi.org/10.1063/1.1610794 (3 pages) | Cited 7 times

Online Publication Date: 9 September 2003

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Thin film materials with a giant dielectric permittivity εr′ ≈ 10 000 and an electromechanical strain of Δh/h ≈ 8% are produced by pulsed-laser deposition. Composite targets containing various different oxides such as BaTiO3, BaO2, BaCO3, and TiO2 powder embedded in the polymer polytetrafluoroethylen (PTFE) are employed for laser ablation. The dielectric permittivities of the films show strong relaxation at frequencies above 10 kHz, a pronounced dependence on layer thickness, and a frequency-dependent activation at lower temperatures. Composite targets as well as films produced from BaF2/PTFE targets show only low permittivities with εr′<20 and do not reveal such phenomena. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Lf Composite materials
77.65.-j Piezoelectricity and electromechanical effects
81.15.Fg Pulsed laser ablation deposition
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.84.Jd Polymers; organic compounds

Continuous-wave millimeter wave generation at 94 GHz in a lithium niobate nonlinear optical waveguide using modulated optical input

Toshihiro Hori and Ki-Hwan Park

Appl. Phys. Lett. 83, 2133 (2003); http://dx.doi.org/10.1063/1.1610246 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2003

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Continuous-wave millimeter wave signals are generated at 94 GHz in a LiNbO3 nonlinear optical waveguide. Optical light with two frequency components is introduced into an optical waveguide, and the generated millimeter waves are obtained from a terminal connected to the metallic traveling waveguide. The configuration is made with a LiNbO3 commercial phase modulator. The generated signals have square-law characteristics between the output and the input power. Experimentally obtained results show that the probable candidate of this physical mechanism is difference frequency generation in nonlinear optical materials. © 2003 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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