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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Light-emission properties of quantum dots embedded in a photonic double-heterostructure nanocavity

Wolfgang C. Stumpf, Masayuki Fujita, Makoto Yamaguchi, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 90, 231101 (2007); http://dx.doi.org/10.1063/1.2746059 (3 pages) | Cited 17 times

Online Publication Date: 4 June 2007

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The authors report on the investigation of the light-emission properties of quantum dots in a photonic double-heterostructure nanocavity. The emission spectrum clearly allows the identification of the cavity and waveguide band edge modes. The frequency and polarization characteristics are in good agreement with three-dimensional finite-difference time-domain calculations. Resonant waveguide band edge mode excitation is demonstrated to reduce the background intensity that does not originate from the cavity and consequently cavity mode properties become evident. Finally, the Q value is estimated and discussed.
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78.67.Hc Quantum dots
78.55.-m Photoluminescence, properties and materials
42.79.Gn Optical waveguides and couplers

Self-phase modulation in photonic-crystal-slab line-defect waveguides

Hisaya Oda, Kuon Inoue, Yu Tanaka, Naoki Ikeda, Yoshimasa Sugimoto, Hiroshi Ishikawa, and Kiyoshi Asakawa

Appl. Phys. Lett. 90, 231102 (2007); http://dx.doi.org/10.1063/1.2746068 (3 pages) | Cited 17 times

Online Publication Date: 4 June 2007

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The authors observed self-phase modulation in spectral domain at 1.50 μm in AlxGa1−xAs-based photonic-crystal-slab line-defect waveguides. Adopting a sample with x = 0.18 has enabled the authors to avoid two-photon absorption, causing undesirable free-carrier-induced refractive-index change. Variation of the observed spectrum with input pulse peak power is well reproduced by theoretical simulation. They find that a 1.6 ps light pulse of 2.5 pJ suffices for causing a phase shift of π in a 1 mm long sample owing to tight light confinement and nonlinear refractive index n2 due to instantaneous optical Kerr effect is (3.8±1.2)×10−13 cm2/W. A possibility of developing ultrafast all-optical switch due to n2 is discussed
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.65.Pc Optical bistability, multistability, and switching, including local field effects

AlGaN based tunable hyperspectral detector

N. Tripathi, J. R. Grandusky, V. Jindal, F. Shahedipour-Sandvik, and L. D. Bell

Appl. Phys. Lett. 90, 231103 (2007); http://dx.doi.org/10.1063/1.2746069 (3 pages) | Cited 4 times

Online Publication Date: 4 June 2007

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The application of III-nitrides to the development of a tunable hyperspectral detector is reported. The device consists of a triangular step barrier provided by a heterostructure of AlN/AlxGa1−xN/GaN. The structure is carefully designed to avoid relaxation of strained layers to prevent further introduction of defects and cracking due to the large tensile strain between different layers of the device. This structure is envisioned for tunable detection of ultraviolet through infrared wavelengths. The particular device structure reported here is expected to span detection energies from ∼ 1 to 2 eV and from 3.4 to  5.4 eV. The adjustable height of the triangular barrier with applied bias voltage provides tunability of the detected wavelength. The results from a first generation device are reported.
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42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Investigation of group delay, loss, and disorder in a photonic crystal waveguide by low-coherence reflectometry

Sylvain Combrié, Nguyen-Vi-Quynh Tran, Evelin Weidner, Alfredo De Rossi, Simone Cassette, Philippe Hamel, Yves Jaouën, Renaud Gabet, and Anne Talneau

Appl. Phys. Lett. 90, 231104 (2007); http://dx.doi.org/10.1063/1.2746080 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2007

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The authors propose highly resolved optical low-coherence reflectometry for investigating low-loss photonic crystal slab waveguides. This technique allows a fast, reliable, and straightforward measurement of the group delay and propagation losses for both TE and TM polarizations. The agreement with theory is very good. These measurements reveal effects related to structural disorder. The versatility and deep physical insight of this measurement technique will play a key role in the study of slow-light devices such as photonic crystal waveguides.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
07.60.Hv Refractometers and reflectometers

Transient property of optically pumped organic film of different fluorescence lifetimes

Takeshi Fukuda, Tomoko Okada, Bin Wei, Musubu Ichikawa, and Yoshio Taniguchi

Appl. Phys. Lett. 90, 231105 (2007); http://dx.doi.org/10.1063/1.2746083 (3 pages) | Cited 3 times

Online Publication Date: 4 June 2007

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The authors have investigated the direct relationship between the fluorescence lifetime (FL) and the transient photoluminescence (PL) response of organic materials to examine the applicability of organic light-emitting diodes as light sources for optical communications. Transient PL responses of organic materials with different FLs were measured as a frequency dependence of PL intensity pumped by a modulated violet laser diode. The authors have revealed that the cutoff frequency of PL intensity is significantly related to FL of an organic film. The −3 dB cutoff frequency of 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DSB) has reached about 160 MHz, which is much higher than that of other organic materials. This is because the FL of DSB is shortest among all the organic materials used in this study.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices

Enhancement of ultraviolet lasing from Ag-coated highly disordered ZnO films by surface-plasmon resonance

A. P. Abiyasa, S. F. Yu, S. P. Lau, Eunice S. P. Leong, and H. Y. Yang

Appl. Phys. Lett. 90, 231106 (2007); http://dx.doi.org/10.1063/1.2746940 (3 pages) | Cited 17 times

Online Publication Date: 4 June 2007

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Large improvement in random lasing action at ultraviolet wavelength has been achieved from highly disordered ZnO films with Ag coating. The lasing threshold can be reduced by two times and slope efficiency can be increased by 5.5 times. The improvement is due to the presence of Ag coating, which enhances the surface coupling of lasing emission from the ZnO films by surface-plasmon resonance and reduces the scattering loss experienced by the random cavity modes. Furthermore, the enhancement of lasing efficiency is dependent on the Ag coating’s surface roughness, which can be controlled through the surface morphology of ZnO films.
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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

Conversion of circularly polarized light into linearly polarized light in anisotropic phase gratings using photo-cross-linkable polymer liquid crystals

Hiroshi Ono, Manabu Nakamura, and Nobuhiro Kawatsuki

Appl. Phys. Lett. 90, 231107 (2007); http://dx.doi.org/10.1063/1.2746938 (3 pages) | Cited 7 times

Online Publication Date: 5 June 2007

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The polarization state of the diffraction light from the polarization holographic grating on varying the polarization conditions of the writing beams has been investigated on the basis of Jones theory. The authors found that the polarization holographic grating, which was fabricated by irradiating the two writing beams with around 0.2 of polarization ellipticity, could convert circularly polarized light into linearly polarized light, and the anisotropic phase grating under above-mentioned condition was really fabricated using the photo-cross-linkable polymer liquid crystal. This function, not observed in the conventional polarization gratings, should be widely applied as highly functionalized optical devices.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals

Very high quantum efficiency in type-II InAs/GaSb superlattice photodiode with cutoff of 12 μm

Binh-Minh Nguyen, Darin Hoffman, Yajun Wei, Pierre-Yves Delaunay, Andrew Hood, and Manijeh Razeghi

Appl. Phys. Lett. 90, 231108 (2007); http://dx.doi.org/10.1063/1.2746943 (3 pages) | Cited 30 times

Online Publication Date: 5 June 2007

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The authors report the dependence of the quantum efficiency on device thickness of type-II InAs/GaSb superlattice photodetectors with a cutoff wavelength around 12 μm. The quantum efficiency and responsivity show a clear delineation in comparison to the device thickness. An external single-pass quantum efficiency of 54% is obtained for a 12 μm cutoff wavelength photodiodes with a π-region thickness of 6.0 μm. The R0A value is kept stable for the range of structure thicknesses allowing for a specific detectivity (2.2×1011 cm math/W).
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Spectrally narrow emission from organic films under continuous-wave excitation

Hajime Nakanotani, Chihaya Adachi, Sadayuki Watanabe, and Ryuzi Katoh

Appl. Phys. Lett. 90, 231109 (2007); http://dx.doi.org/10.1063/1.2746958 (3 pages) | Cited 9 times

Online Publication Date: 5 June 2007

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The authors observed a narrow emission from a 500-nm-thick codeposited organic thin film, 6 wt % 4,4′-bis[(N-carbazole)styryl]-biphenyl (BSB-Cz) doped into a 4,4′-bis(N-carbazole)-biphenyl host, under continuous-wave excitation. Although they observed no clear threshold characteristics on the spectral narrowing, they found that the emission centered at a wavelength of λASE = 462 nm, corresponding to the zero to one transition of BSB-Cz, has a transverse electric mode with a narrow full width at half maximum of λFWHM = 3.4 nm, indicating the occurrence of amplified spontaneous emission. No excited state absorptions of singlet and triplet excited states of BSB-Cz are confirmed around λASE, leading to large net gain for the light amplification.
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78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics

Continuous wave and passively Q-switched laser performance of a Nd-doped mixed crystal Nd:Lu0.5Gd0.5VO4

Haohai Yu, Huaijin Zhang, Zhengping Wang, Jiyang Wang, Yonggui Yu, Zongshu Shao, Minhua Jiang, and Xingyu Zhang

Appl. Phys. Lett. 90, 231110 (2007); http://dx.doi.org/10.1063/1.2747186 (3 pages) | Cited 21 times

Online Publication Date: 5 June 2007

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The authors reported continuous wave (cw) and passively Q-switched laser performances of Nd:Lu0.5Gd0.5VO4 crystal at 1.06 μm. cw output power of 6.65 W was obtained under the incident pump power of 13.75 W with slop efficiency of 51%. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 6.2 ns, 192.5 μJ, and 31.06 kW, respectively, with Cr4+ doped yttrium aluminum garnet crystals as the saturable absorbers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

16.5 μm quantum cascade detector using miniband transport

Fabrizio R. Giorgetta, Esther Baumann, Marcel Graf, Lassaad Ajili, Nicolas Hoyler, Marcella Giovannini, Jérôme Faist, Daniel Hofstetter, Peter Krötz, and Guido Sonnabend

Appl. Phys. Lett. 90, 231111 (2007); http://dx.doi.org/10.1063/1.2743955 (3 pages) | Cited 15 times

Online Publication Date: 6 June 2007

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The authors report on an InP based photovoltaic quantum cascade detector operating at 16.5 μm and using miniband-based vertical transport. This concept allowed the construction of a longitudinal optical phonon extraction stair with two rungs without touching on a high device resistance. At 10 K, they observed a responsivity of 1.72 mA/W and a Johnson noise limited detectivity of 2.2×109 Jones. Altogether, this design resulted in detection at temperatures of up to 90 K with a lower bandwidth limit of 200 MHz imposed by the measurement setup.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes

Optical response of artificial opals oriented along the ΓX direction

J. F. Galisteo-López, M. Galli, A. Balestreri, L. C. Andreani, and C. López

Appl. Phys. Lett. 90, 231112 (2007); http://dx.doi.org/10.1063/1.2746936 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2007

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The optical response of artificial opals in the surroundings of the [100] crystallographic direction has been measured by means of microreflectance and transmittance spectroscopies. The results indicate that for such sample orientation, the optical properties are determined entirely by low dispersion bands responsible for out-of-plane diffraction. This is corroborated by phase-sensitive spectroscopy which shows strong anomalies in the measured phase above the onset of diffraction. Such anomalies translate into group velocity values of ±c/20, evidencing slow and superluminal light propagation. These findings could be relevant in developing future routes for enhanced light-matter interaction.
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42.70.-a Optical materials

Sampling of broadband terahertz pulses with thick electro-optic crystals

Tobias Kampfrath, Jan Nötzold, and Martin Wolf

Appl. Phys. Lett. 90, 231113 (2007); http://dx.doi.org/10.1063/1.2746939 (3 pages) | Cited 11 times

Online Publication Date: 7 June 2007

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The authors show by experiment and theory that thick electro-optic crystals are suitable media for sampling electromagnetic radiation from 0.3 to 50 THz with 10 fs visible laser pulses. For example, the detection of frequencies above 10 THz with a 250 μm thick, ⟨110⟩-oriented ZnTe crystal is as efficient as that with a 10 μm thin crystal. This surprising behavior and a much flatter detector response arise because phase-matching oscillations are greatly smeared out by the broad spectrum of the sampling pulse and the crystal dispersion.
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78.20.Jq Electro-optical effects
78.66.Hf II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Photonic crystal Mach-Zehnder interferometer based on self-collimation

Deyin Zhao, Jie Zhang, Peijun Yao, Xunya Jiang, and Xiyao Chen

Appl. Phys. Lett. 90, 231114 (2007); http://dx.doi.org/10.1063/1.2746942 (3 pages) | Cited 27 times

Online Publication Date: 7 June 2007

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The authors design a photonic crystal Mach-Zehnder interferometer by utilizing the self-collimated beams and the bending and splitting mechanisms of line defects. Using this interferometer, they investigate the phase shift of the reflected and transmitted self-collimated beams over the line defects. In addition, on the basis of the intensity-asymmetric unidirectional-output design, they demonstrate that such interferometers can function as an intensity detector or an ultrafast optical switch when the material of photonic crystal is nonlinear.
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42.70.Qs Photonic bandgap materials
07.60.Ly Interferometers
42.15.Eq Optical system design

High current density GaN/CsBr heterojunction photocathode with improved photoyield

Zhi Liu, Yun Sun, Piero Pianetta, Juan R. Maldonado, R. F. W. Pease, and Scott Schuetter

Appl. Phys. Lett. 90, 231115 (2007); http://dx.doi.org/10.1063/1.2746959 (3 pages) | Cited 4 times

Online Publication Date: 7 June 2007

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A four fold improvement in photoyield has been observed in GaN films coated with CsBr films (CsBr/GaN) relative to CsBr/Cr photocathodes reported in previous studies. A model is presented involving photoemission from intraband states in the CsBr film and direct electron injection through the CsBr film from the GaN substrate. The lifetime of the films at high current density >90 A/cm2 is limited by the temperature rise in the GaN films caused by the high photon absorption at 257 nm. The lifetime can be improved by utilizing a cooled substrate or a high thermal conductivity substrate under the GaN films.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Mid-infrared AlxIn1−xSb light-emitting diodes

M. K. Haigh, G. R. Nash, S. J. Smith, L. Buckle, M. T. Emeny, and T. Ashley

Appl. Phys. Lett. 90, 231116 (2007); http://dx.doi.org/10.1063/1.2745256 (3 pages) | Cited 11 times

Online Publication Date: 11 June 2007

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The properties of AlxIn1−xSb light-emitting diodes (LEDs) have been investigated as a function of aluminum concentrations between 0% and 8.8%. By varying the aluminum concentration it is possible to tailor the peak emission wavelength to match the characteristic absorption of CO2, CO, CH4, NO, and NO2, making these diodes suitable for use in infrared gas sensing applications. The total emitted power and internal quantum efficiency were found to have maxima of 27 mW/cm2 and 4.2%, respectively, at a composition of 2.5%, where the peak emission was found to be 5.3 μm, making LEDs of this composition particularly suited to the detection of NO.
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85.60.Jb Light-emitting devices

Polarization-dependent beam switch based on an M-plane GaN/AlN distributed Bragg reflector

D. M. Schaadt, O. Brandt, Sandip Ghosh, T. Flissikowski, U. Jahn, and H. T. Grahn

Appl. Phys. Lett. 90, 231117 (2007); http://dx.doi.org/10.1063/1.2747189 (3 pages) | Cited 4 times

Online Publication Date: 7 June 2007

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The authors demonstrate a two-color distributed Bragg reflector (DBR) consisting of 20 periods of alternating [1math00]-oriented (M-plane) AlN and GaN layers grown on LiAlO2 by molecular-beam epitaxy. Due to the birefringent nature of GaN and AlN, the wavelength region of the stop band depends on the polarization state of the incoming light beam (parallel or perpendicular) with respect to the c axis of the wurtzite crystal structure. In the wavelength range, where the transmittance for one polarization direction and the reflectance for the orthogonal polarization direction are both high, the DBR can be used as a beam switch or polarization filter.
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42.82.Gw Other integrated-optical elements and systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers

Integration of optical waveguides and microfluidic channels both fabricated by femtosecond laser irradiation

Roberto Osellame, Valeria Maselli, Rebeca Martinez Vazquez, Roberta Ramponi, and Giulio Cerullo

Appl. Phys. Lett. 90, 231118 (2007); http://dx.doi.org/10.1063/1.2747194 (3 pages) | Cited 40 times

Online Publication Date: 7 June 2007

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A femtosecond laser is used to fabricate both microfluidic channels and high quality optical waveguides, intersecting each other on a single glass substrate. Fluorescence in fluids filling the microfluidic channels has been selectively excited in several points by coupling light in the optical waveguides. Waveguide-microchannel integration opens several prospects for in situ sensing in lab-on-a-chip devices.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.86.+b Optical workshop techniques
42.62.-b Laser applications

Temperature dependencies of annealing behaviors of GaInNAsSb/GaNAs quantum wells for long wavelength dilute-nitride lasers

Hopil P. Bae, Seth R. Bank, Homan B. Yuen, Tomas Sarmiento, Evan R. Pickett, Mark A. Wistey, and James S. Harris

Appl. Phys. Lett. 90, 231119 (2007); http://dx.doi.org/10.1063/1.2746944 (3 pages) | Cited 2 times

Online Publication Date: 11 June 2007

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The photoluminescence (PL) spectra of GaInNAs(Sb)/GaNAs quantum well samples emitting around 1.5 μm, annealed at different temperatures and for different durations, were compared. Two distinct processes with widely different temperature dependencies are identified: PL intensity improvement at the beginning of annealing and PL intensity degradation when overannealed. The degradation process has a much steeper temperature dependence than the improvement process, so lower-temperature, longer-duration annealings result in both a higher photoluminescence intensity and a broader process window than higher-temperature, shorter-duration annealings. The lowest threshold of 1.55 GaInNAs(Sb) lasers up to now was obtained exclusively with short, hot annealings, this finding offers another method of further improving dilute-nitride laser performance. Similar trends are found for different compositions and thicknesses of GaInNAs(Sb).
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.67.De Quantum wells
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.72.Cc Kinetics of defect formation and annealing
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Correlation of spectral luminescence with threading dislocations in green-light-emitting InGaN quantum wells

J. C. Brooksby, J. Mei, and F. A. Ponce

Appl. Phys. Lett. 90, 231901 (2007); http://dx.doi.org/10.1063/1.2746062 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2007

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A direct correlation has been established between the spatial variation of spectral luminescence and the distribution of threading dislocations in a green-light-emitting InGaN quantum well structure grown on a sapphire substrate. Transmission electron microscopy and monochromatic cathodoluminescence images, taken from the same region, indicate that the nature of the quantum well emission is influenced by the microstructure of the underlying GaN. The microstructure is defined by threading dislocations that reflect a columnar structure with low-angle grain boundaries. A strong correlation is observed between this microstructure and the peak and low-energy portion of the quantum well luminescence, with threading dislocations as boundaries between bright and darker regions. The high-energy portion of the luminescence is localized and is generally complementary to the rest of the spectrum.
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78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
61.72.Mm Grain and twin boundaries
61.72.S- Impurities in crystals

Layer rotation mechanism in the chiral smectic C phase

J. N. Jang, A. B. Davey, and W. A. Crossland

Appl. Phys. Lett. 90, 231902 (2007); http://dx.doi.org/10.1063/1.2746410 (3 pages)

Online Publication Date: 5 June 2007

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The authors propose a model for the layer rotation of the chiral smectic C (SmC*) phase, which is intended to give answers to some basic questions about smectic layer rotation. They have proposed that layer rotation is related to the electroclinic effect, by which an induced asymmetric population density of the director for each asymmetric ac cycle is induced. In our modeling, the driving force for the layer rotation is the deformation of the molecular coupling configuration and a volume change by the tilt cone rotation.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals

Separation of coherent and incoherent contributions to reflectance difference spectra

K. Schmidegg and P. Zeppenfeld

Appl. Phys. Lett. 90, 231903 (2007); http://dx.doi.org/10.1063/1.2746421 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2007

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The authors present a method for the analysis of azimuthal dependent reflectance difference spectroscopy data that enables a separation of coherent and incoherent contributions to reflectance difference spectra. The latter can originate from back side reflections of transparent films if their thickness is larger than the coherence length of the light. Furthermore, instrument artifacts can be suppressed and additional contributions with different optical eigenaxes can be identified.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

Effects of surface elasticity and residual surface tension on the natural frequency of microbeams

Gang-Feng Wang and Xi-Qiao Feng

Appl. Phys. Lett. 90, 231904 (2007); http://dx.doi.org/10.1063/1.2746950 (3 pages) | Cited 88 times

Online Publication Date: 5 June 2007

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Surface effects often play a significant role in the physical properties of micro- and nanosized materials and structures. In this letter, the authors presented a theoretical model directed towards investigation of the effects of both surface elasticity and residual surface tension on the natural frequency of microbeams. A thin surface layer was introduced on the upper and lower surfaces to rationalize the near-surface material properties that are different from the bulk material. An explicit solution is derived for the natural frequency of microbeams with surface effects. This study might be helpful for the design of microbeam-based sensors and some related measurement techniques.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Thermal energy exchange between carbon nanotube and air

Ming Hu, Sergei Shenogin, Pawel Keblinski, and Nachiket Raravikar

Appl. Phys. Lett. 90, 231905 (2007); http://dx.doi.org/10.1063/1.2746954 (3 pages) | Cited 10 times

Online Publication Date: 5 June 2007

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Using molecular dynamics simulations the authors impose a heat flux between single-walled carbon nanotubes and air to study thermal interfacial conductance. They estimate that the nanotube-air interfacial thermal conductance is about 0.1 MW/m2 K at room temperature and atmospheric pressure. The associated interfacial thermal resistance is equivalent to the resistance of 250 nm thick layer of air. They also show that the interfacial resistance is a strong function of the interaction parameters between air atoms and carbon nanotubes.
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73.40.-c Electronic transport in interface structures
68.35.Md Surface thermodynamics, surface energies

Femtosecond nonlinear optical properties of lead-germanium oxide amorphous films

Diego Rativa, Renato E. de Araujo, Cid B. de Araújo, Anderson S. L. Gomes, and Luciana R. P. Kassab

Appl. Phys. Lett. 90, 231906 (2007); http://dx.doi.org/10.1063/1.2747174 (3 pages) | Cited 13 times

Online Publication Date: 6 June 2007

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The nonlinear (NL) response of lead-germanium oxide amorphous films was investigated using a Ti:saphire laser delivering pulses of ≈ 150 fs at 800 nm. The Kerr shutter technique was employed to reveal the time response of the nonlinearity that is smaller than 150 fs. The sign and magnitude of the nonlinearity were obtained using a novel technique called thermally managed eclipse Z scan which allows the simultaneous characterization of cumulative and noncumulative NL effects. The NL refractive index of electronic origin, n2 ≈ 2×10−17 m2/W, and the NL absorption coefficient, α2 ≈ 3×103 cm/GW, were determined.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.-w Optical properties of specific thin films
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
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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