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13 Aug 2012

Volume 101, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages)

Judson D. Ryckman and S. M. Weiss
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A “low-deformation mirror” micro-oscillator with ultra-low optical and mechanical losses

E. Serra, A. Borrielli, F. S. Cataliotti, F. Marin, F. Marino, A. Pontin, G. A. Prodi, and M. Bonaldi

Appl. Phys. Lett. 101, 071101 (2012); http://dx.doi.org/10.1063/1.4745510 (4 pages) | Cited 2 times

Online Publication Date: 13 August 2012

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We report on the mechanical losses measured in a “low-deformation mirror” micro-oscillator designed to reduce as much as possible the strain in the coating layer and the resulting energy dissipation. The deposition of the highly reflective coating layer has been fully integrated in the micro-machining process. We measured at cryogenic temperature a mechanical quality factor up to 105 and an optical finesse of about 4×104, and simulations show that the device can manage input powers of a few mW at 4.2 K. These features make the device very promising for quantum optics experiments.
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85.60.Bt Optoelectronic device characterization, design, and modeling
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
84.30.Ng Oscillators, pulse generators, and function generators

Observation of the continuous transformation of a four level laser into a two level system

J. D. Hewitt, J. D. Readle, and J. G. Eden

Appl. Phys. Lett. 101, 071102 (2012); http://dx.doi.org/10.1063/1.4745511 (4 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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A longstanding and fundamental question of laser and maser physics concerns the energy separation (Δϵ) required between the pumped and lasing states of a three (or four) level system. We observe a four level laser gradually transform into a two level (nonlasing) system by photoassociating Cs-Ar thermal atomic pairs and monitoring subsequent stimulated emission on the 6p2P3/2 → 6s2S1/2 (D2) transition of Cs at 852.1 nm. Laser excitation spectra demonstrate that the value of Δϵ below which the system rapidly assumes the form of a two level structure and lasing ceases is ∼ 0.7kT which corresponds to a Boltzmann factor (exp[−Δϵ/kT]) of 0.5.
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82.30.Nr Association, addition, insertion, cluster formation
82.50.-m Photochemistry
32.80.Xx Level crossing and optical pumping

Optical limiting studies of ZnO nanotops and its polymer nanocomposite films

P. C. Haripadmam, M. K. Kavitha, Honey John, Bindu Krishnan, and Pramod Gopinath

Appl. Phys. Lett. 101, 071103 (2012); http://dx.doi.org/10.1063/1.4745605 (5 pages) | Cited 2 times

Online Publication Date: 13 August 2012

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In the present work, we have investigated the optical limiting property of zinc oxide (ZnO) nanotop colloids and nanocomposite films of polymer-ZnO nanotops, using Z-scan technique. ZnO nanotops are prepared using two different capping agents. Films of polymethyl methacrylate-ZnO nanotop composite are fabricated for two concentrations of ZnO using spin coating technique. On exposing the nanocolloids to a pulsed nanosecond laser, the two photon absorption coefficient is enhanced with increase in applied fluence and particle size. The efficiency of limiting is found to be enhanced for the composite films, opening a way towards optoelectronic device fabrication.
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78.67.Sc Nanoaggregates; nanocomposites
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.70.Dd Colloids
FREE

Low mode volume slotted photonic crystal single nanobeam cavity

Judson D. Ryckman and S. M. Weiss

Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages) | Cited 3 times

Online Publication Date: 13 August 2012

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We present and experimentally demonstrate a slotted photonic crystal single nanobeam cavity in silicon. The slot geometry is exploited to achieve ultra-small effective mode volumes, ∼0.025(λ/n)3, more than an order of magnitude smaller than traditional nanobeam cavities. A continuous slot and a tapered photonic crystal design are implemented to achieve experimental quality factors near 104. This device structure offers a unique platform for achieving enhanced light-matter interactions and could be used to benefit a variety of applications including non-linear optics, cavity quantum electro-dynamics, sensing, optical modulation, and nano-optomechanics.
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42.70.Qs Photonic bandgap materials
42.82.-m Integrated optics

In-situ photoluminescence monitoring of GaN in plasma exposure

Miao-Gen Chen, Keiji Nakamura, Yoshitaka Nakano, Sen-Jiang Yu, and Hideo Sugai

Appl. Phys. Lett. 101, 071105 (2012); http://dx.doi.org/10.1063/1.4745917 (4 pages)

Online Publication Date: 13 August 2012

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We have investigated in-situ photoluminescence properties of GaN surfaces exposed to Ar plasma. With increasing plasma exposure time, both intensities of near-band-edge (NBE) peak and yellow band luminescence (YL) significantly decrease, whereas that of blue band luminescence (BL) is seen to gradually increase. Additionally, the YL/NBE intensity ratio is almost invariant, but the BL/NBE intensity ratio increases dramatically with increasing the plasma exposure time. The results suggest that the increase in the BL intensity is probably due to the plasma-induced damage accumulation and the in-situ monitoring of the BL/NBE intensity ratio can be used to observe the plasma-induced damage.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
52.77.Dq Plasma-based ion implantation and deposition
71.20.Nr Semiconductor compounds

Optical microdiscus resonators by flattening microspheres

Ganapathy Senthil Murugan, James S. Wilkinson, and Michalis N. Zervas

Appl. Phys. Lett. 101, 071106 (2012); http://dx.doi.org/10.1063/1.4746256 (4 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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A “soften-and-squash” fabrication technique has been demonstrated to controllably deform optical microspheres and form microdiscus resonators with improved surface quality. The characteristic shape of the microdiscus results in superior mode control, and the annealing involved in the fabrication process leads to quality factors (Q) exceeding 105, which is about two orders of magnitude higher than the initial microspheres.
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42.79.-e Optical elements, devices, and systems
07.10.Cm Micromechanical devices and systems

Experimental demonstration of an active phase randomization and monitor module for quantum key distribution

Shi-Hai Sun and Lin-Mei Liang

Appl. Phys. Lett. 101, 071107 (2012); http://dx.doi.org/10.1063/1.4746402 (5 pages)

Online Publication Date: 13 August 2012

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Phase randomization is a very important assumption in the BB84 quantum key distribution (QKD) system with weak coherent source; otherwise, eavesdropper may spy the final key. In this Letter, a stable and monitored active phase randomization scheme for the one-way and two-way QKD system is proposed and demonstrated in experiments. Furthermore, our scheme gives an easy way for Alice to monitor the degree of randomization in experiments. Therefore, we expect our scheme to become a standard part in future QKD systems due to its secure significance and feasibility.
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03.67.Dd Quantum cryptography and communication security
02.50.Cw Probability theory

Excitation of a high-Q subradiant resonance mode in mirrored single-gap asymmetric split ring resonator terahertz metamaterials

Ibraheem Al-Naib, Ranjan Singh, Carsten Rockstuhl, Falk Lederer, Sebastien Delprat, David Rocheleau, Mohamed Chaker, Tsuneyuki Ozaki, and Roberto Morandotti

Appl. Phys. Lett. 101, 071108 (2012); http://dx.doi.org/10.1063/1.4745790 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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We propose a mirrored arrangement of asymmetric single split ring resonators (ASRs) that dramatically enhances the quality factor of the inductive-capacitive resonance. In a regular non-mirrored arrangement, the surface current modes are all oriented in phase. Hence, light scattered by individual ASRs interferes constructively. In contrast, the proposed configuration sustains surface currents that are oppositely oriented for neighboring ASRs, in turn leading to the cancellation of the net dipole moment accompanied by destructive interference of the scattered fields. The proposed arrangement holds promise to suppress radiation losses in terahertz, microwave and infrared plasmonic metamaterials.
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42.70.-a Optical materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Enhancement of spontaneous emission in three-dimensional low refractive-index photonic crystals with designed defects

Zongsong Gan, Baohua Jia, Jing-Feng Liu, Xue-Hua Wang, and Min Gu

Appl. Phys. Lett. 101, 071109 (2012); http://dx.doi.org/10.1063/1.4745923 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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In this work, we demonstrate that low refractive-index three-dimensional photonics crystals with a planar defect, fabricated with the direct laser writing method, can be used to effectively enhance the spontaneous emission (SE) of semiconductor quantum dots (QDs). To achieve this, we develop a controllable and reliable method to integrate quantum dots into the defect-embedded photonic crystals (PCs). Although the overlapping of different direction stop gaps in low refractive-index defect-free three-dimensional photonic crystals imposes a challenge to realize spontaneous emission enhancement at the band edge wavelength, we achieve a 15% enhancement of the spontaneous emission by introducing a tailored planar defect.
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78.67.Hc Quantum dots
42.70.Qs Photonic bandgap materials
61.72.-y Defects and impurities in crystals; microstructure
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.45.+h Stimulated emission

Micromachining along a curve: Femtosecond laser micromachining of curved profiles in diamond and silicon using accelerating beams

A. Mathis, F. Courvoisier, L. Froehly, L. Furfaro, M. Jacquot, P. A. Lacourt, and J. M. Dudley

Appl. Phys. Lett. 101, 071110 (2012); http://dx.doi.org/10.1063/1.4745925 (3 pages) | Cited 6 times

Online Publication Date: 14 August 2012

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We report femtosecond laser micromachining of micron-size curved structures using tailored accelerating beams. We report surface curvatures as small as 70 μm in both diamond and silicon, which demonstrates the wide applicability of the technique to materials that are optically transparent or opaque at the pump laser wavelength. We also report the machining of curved trenches in silicon. Our results are consistent with an ablation-threshold model based on calculated local beam intensity, and we also observe asymmetric debris deposition which is interpreted in terms of the optical properties of the incident accelerating beam.
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78.47.J- Ultrafast spectroscopy (<1 psec)
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)
42.62.Cf Industrial applications
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.20.Wk Machining, milling

Gallium free type II InAs/InAsxSb1-x superlattice photodetectors

T. Schuler-Sandy, S. Myers, B. Klein, N. Gautam, P. Ahirwar, Z.-B. Tian, T. Rotter, G. Balakrishnan, E. Plis, and S. Krishna

Appl. Phys. Lett. 101, 071111 (2012); http://dx.doi.org/10.1063/1.4745926 (3 pages)

Online Publication Date: 14 August 2012

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We report on a mid-wave infrared (λ50% cut-off ∼5.4 μm at 77 K) Ga-free Type II InAs/InAsxSb1-x (x = 0.65) superlattice detector Radiometric measurements reveal a quantum efficiency of 20% (λ = 4 μm, 77 K) with a dark current density of 2.1 × 10−4 A/cm2 (−10 mV) with spectral response observable up to 210 K. Although the Shockley-Read-Hall lifetime is expected to be longer for Ga-free superlattices, the dark current density is larger than that of conventional InAs/GaSb superlattice detectors. This is attributed to increased probability of carrier tunneling due to reduced valence and conduction band-offsets in InAs/InAsSb SL system.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

A passively mode-locked quantum-dot laser operating over a broad temperature range

J. K. Mee, M. T. Crowley, N. Patel, D. Murrell, R. Raghunathan, A. Aboketaf, A. Elshaari, S. F. Preble, P. Ampadu, and L. F. Lester

Appl. Phys. Lett. 101, 071112 (2012); http://dx.doi.org/10.1063/1.4746266 (4 pages)

Online Publication Date: 14 August 2012

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Broad temperature operation is demonstrated from 20 to 110 °C in a 5-GHz monolithic two-section InAs/GaAs quantum dot passively mode-locked laser with an optimized absorber to gain section length ratio of 0.11. Stable pulses of less than 19 ps full-width-half-maximum are measured over this entire temperature range. For a grounded absorber, mode-locking from the ground-state occurred over the range 20–92 °C, dual-mode lasing involving both ground and excited states from 93 to 98 °C and exclusively from the excited-state from 99 to 110 °C. The observed broad temperature operation agrees with theoretical analysis based on measured gain and absorption data that predicted improved temperature performance for a short absorber. The results are promising for the development of temperature-insensitive pulsed sources for uncooled applications such as data multiplexing and optical clocking.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Čerenkov difference frequency generation in a two-dimensional nonlinear photonic crystal

C. D. Chen, X. P. Hu, Y. L. Xu, P. Xu, G. Zhao, and S. N. Zhu

Appl. Phys. Lett. 101, 071113 (2012); http://dx.doi.org/10.1063/1.4746408 (4 pages) | Cited 2 times

Online Publication Date: 14 August 2012

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We present experimental realization of Čerenkov difference frequency generation (CDFG) in a 2-dimentional rectangular periodically poled LiTaO3. The backward reciprocal vector of the nonlinear photonic crystal accelerates the phase velocity of the nonlinear polarization wave so as to exceed the phase speed limit of achieving Čerenkov down-conversions in this normal dispersion medium. Some characteristics of CDFG, such as radiation angles, pumping power, and pulse temporal overlapping dependences were discussed. The experimental results matched well with theoretical predictions.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials

Broadband opto-mechanical phase shifter for photonic integrated circuits

Xiang Guo, Chang-Ling Zou, Xi-Feng Ren, Fang-Wen Sun, and Guang-Can Guo

Appl. Phys. Lett. 101, 071114 (2012); http://dx.doi.org/10.1063/1.4746761 (5 pages)

Online Publication Date: 14 August 2012

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A broadband opto-mechanical phase shifter for photonic integrated circuits is proposed and numerically investigated. The structure consists of a mode-carrying waveguide and a deformable non-mode-carrying nanostring, which are parallel with each other. Since the nanostring can be deflected by the optical gradient force between the waveguide and the nanostring, the effective refractive indices of the waveguide will be changed and a phase shift will be generated. The phase shift under different geometry sizes, launched powers and boundary conditions are calculated and the dynamical properties as well as the thermal noise’s effect are also discussed. It is demonstrated that a π phase shift can be realized with only about 0.64 mW launched power and 50 μm long nanostring. The proposed phase shifter may find potential usage in future investigation of photonic integrated circuits.
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42.82.-m Integrated optics
42.79.-e Optical elements, devices, and systems

Highly complex optical signal generation using electro-optical systems with non-linear, non-invertible transmission functions

José J. Suárez-Vargas, Bicky A. Márquez, and Jorge A. González

Appl. Phys. Lett. 101, 071115 (2012); http://dx.doi.org/10.1063/1.4747151 (4 pages)

Online Publication Date: 16 August 2012

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We present a scheme whereby a static non-linear, non-invertible transmission function performed by the electro-optic Mach-Zehnder modulator produces highly complex optical chaos. The scheme allows the deterministic transformation of low-dimensional band-limited chaotic signals into much higher-dimensional structures with broadband spectra and without using any delay elements or feedback. Standard benchmark tests show that all the considered complexity indices are highly increased due to this transformation in a controlled fashion. This mechanism allows the design of simple optoelectronic delayed oscillators with extremely complex chaotic output.
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42.79.Hp Optical processors, correlators, and modulators
42.87.-d Optical testing techniques
42.15.Eq Optical system design
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics

High-order harmonic generation at 4 MHz as a light source for time-of-flight photoemission spectroscopy

Cheng-Tien Chiang, Alexander Blättermann, Michael Huth, Jürgen Kirschner, and Wolf Widdra

Appl. Phys. Lett. 101, 071116 (2012); http://dx.doi.org/10.1063/1.4746264 (4 pages) | Cited 2 times

Online Publication Date: 16 August 2012

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We demonstrate high-order harmonic generation (HHG) at 4 MHz driven by a long-cavity femtosecond laser oscillator. The laser output is used directly in a tight focusing geometry, where the harmonics are generated from a gas jet with high backing pressure. The harmonic light source is applied to time-of-flight photoemission spectroscopy, and the characteristic electronic structure of Cu(111) is measured. Our results suggest a straightforward design of high-order harmonic generation at megahertz repetition rate and pave the way for applications in electron spectroscopy and microscopy.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
79.60.-i Photoemission and photoelectron spectra
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Design considerations for large-aperture single-mode oxide-confined vertical-cavity surface-emitting lasers

V. P. Kalosha, N. N. Ledentsov, and D. Bimberg

Appl. Phys. Lett. 101, 071117 (2012); http://dx.doi.org/10.1063/1.4746422 (4 pages)

Online Publication Date: 16 August 2012

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The output modal content of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) crucially depends upon the thickness of the low-index oxide aperture, its position with respect to the standing waves of the transverse-longitudinal modes and the separation from the cavity. Three-dimensional cold-cavity optical modes of typical AlGaAs/GaAs VCSELs at 850 nm were simulated to study these dependencies quantitatively taking into account the field diffraction and the material dispersion. Modification of one or two periods of the distributed Bragg reflector by positioning the thin oxidized aperture layers in the mode nodes allows single-mode regime to extend to the aperture diameters as large as 10 μm.
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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
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The “quasi-stable” lipid shelled microbubble in response to consecutive ultrasound pulses

D. H. Thomas, M Butler, T. Anderson, M. Emmer, H. Vos, M. Borden, E. Stride, N. de Jong, and V. Sboros

Appl. Phys. Lett. 101, 071601 (2012); http://dx.doi.org/10.1063/1.4746258 (4 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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Controlled microbubble stability upon exposure to consecutive ultrasound exposures is important for increased sensitivity in contrast enhanced ultrasound diagnostics and manipulation for localised drug release. An ultra high-speed camera operating at 13 × 106 frames per second is used to show that a physical instability in the encapsulating lipid shell can be promoted by ultrasound, causing loss of shell material that depends on the characteristics of the microbubble motion. This leads to well characterized disruption, and microbubbles follow an irreversible trajectory through the resonance peak, causing the evolution of specific microbubble spectral signatures.
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87.50.yg Biophysical mechanisms of interaction
87.63.D- Ultrasonography
87.64.M- Optical microscopy
87.85.-d Biomedical engineering
43.35.Wa Biological effects of ultrasound, ultrasonic tomography
47.55.dd Bubble dynamics

Role of entrapped vapor bubbles during microdroplet evaporation

Shawn A. Putnam, Larry W. Byrd, Alejandro M. Briones, Michael S. Hanchak, Jamie S. Ervin, and John G. Jones

Appl. Phys. Lett. 101, 071602 (2012); http://dx.doi.org/10.1063/1.4745009 (4 pages)

Online Publication Date: 17 August 2012

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On superheated surfaces, the air bubble trapped during impingement grows into a larger vapor bubble and oscillates at the frequency predicted for thermally induced capillary waves. In some cases, the entrapped vapor bubble penetrates the droplet interface, leaving a micron-sized coffee-ring pattern of pure fluid. Vapor bubble entrapment, however, does not influence the evaporation rate. This is also true on laser heated surfaces, where a laser can thermally excite capillary waves and induce bubble oscillations over a broad range of frequencies, suggesting that exciting perturbations in a pinned droplets interface is not an effective avenue for enhancing evaporative heat transfer.
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47.55.dr Interactions with surfaces
47.80.Jk Flow visualization and imaging
68.03.Fg Evaporation and condensation of liquids
47.35.Pq Capillary waves
47.54.De Experimental aspects
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An oscillation-free actuation of fluidic lens for optical beam control

Yiin-Kuen Fuh (傅尹坤), Wei-Chi Huang (黃維麒), Ying-Sheng Lee (李瀛生), and Shyong Lee (李雄)

Appl. Phys. Lett. 101, 071901 (2012); http://dx.doi.org/10.1063/1.4745771 (3 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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We demonstrate an oscillation-free implementation of an optical beam control device with reconfigurable fluidic lens. In the activation state, the incident light passing through the interfacing medium (water or air) is diverged by the deformed plano-concave fluidic lens, resulting in a dark state. In the non-activation state, the elastic membrane recovers to its original state of the flat interface—this has the effect of transmitting the incident light and opening the switch. We also demonstrated a white-light switch with tunable response times ranging from 50 ms to 200 ms. The actuation mechanism has tremendous potential in light shutters, variable optical attenuators, and displays.
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42.79.Bh Lenses, prisms and mirrors
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Epitaxial growth and metal-insulator transition of vanadium oxide thin films with controllable phases

Y. D. Ji, T. S. Pan, Z. Bi, W. Z. Liang, Y. Zhang, H. Z. Zeng, Q. Y. Wen, H. W. Zhang, C. L. Chen, Q. X. Jia, and Y. Lin

Appl. Phys. Lett. 101, 071902 (2012); http://dx.doi.org/10.1063/1.4745843 (5 pages) | Cited 3 times

Online Publication Date: 13 August 2012

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Vanadium oxide thin films with well controlled phases such as rhombohedra V2O3 and monoclinic VO2 were synthesized on Al2O3 (0001) substrates by optimizing the processing parameters of a polymer assisted deposition technique. X-ray diffraction and high-resolution transmission electron microscopy studies revealed that both V2O3 and VO2 films can be well controlled with good epitaxial quality. The temperature dependency of electrical resistivity demonstrated sharp metal-insulator transitions (MITs) for V2O3 and VO2 films. The crystallinity and the strains in the films are believed to play critical roles in determining the MIT properties.
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68.55.at Other materials
71.30.+h Metal-insulator transitions and other electronic transitions

Plasmon-induced near-infrared electrochromism based on transparent conducting nanoparticles: Approximate performance limits

S.-Y. Li, G. A. Niklasson, and C. G. Granqvist

Appl. Phys. Lett. 101, 071903 (2012); http://dx.doi.org/10.1063/1.4739792 (3 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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Electrochromism can be induced in electrochemically post-treated nanoparticles of wide band gap transparent conductors. We model this recently observed phenomenon by effective medium theory applied to nanoparticles of In2O3:Sn, which are represented as a free-electron plasma with tin ions screened according to the random phase approximation corrected for electron exchange. This semi-quantitative theory is used to derive approximate performance limits showing that high luminous transmittance (e.g., 60%) can be combined with efficient absorption of solar energy and concomitant low solar transmittance (∼34%), thereby documenting that plasmonic electrochromism is of interest for energy efficient fenestration.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
72.80.Jc Other crystalline inorganic semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Thermoluminescence studies on γ-irradiated Mn:Li2B4O7 single crystals

S. Kar, S. Bairagi, C. Debnath, S. Verma, and K. S. Bartwal

Appl. Phys. Lett. 101, 071904 (2012); http://dx.doi.org/10.1063/1.4747147 (4 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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Manganese doped Li2B4O7 (LTB) crystals were grown by Czochralski technique and various kinetic parameter of thermoluminescence (TL) were measured. Crystals were irradiated with different γ-dose using Co60 source. Thermoluminescence curves were recorded at various heating rates. Trap depth and frequency factor were calculated. Fading of Mn: Li2B4O7 was found only ∼5%-6% in 6 months. Thermoluminescence intensity of Mn: Li2B4O7 was found highly sensitive to the mass of the material, and it varies abruptly with mass change of +/− 1 mg, irradiated with the same dose. Therefore, the accuracy in mass is important parameter for thermoluminescence dosimeter badge.
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78.60.Kn Thermoluminescence
81.10.Fq Growth from melts; zone melting and refining
81.40.Gh Other heat and thermomechanical treatments
61.80.Ed γ-ray effects
61.82.Ms Insulators

Laser irradiation-induced α to δ phase transformation in Bi2O3 ceramics and nanowires

M. Vila, C. Díaz-Guerra, and J. Piqueras

Appl. Phys. Lett. 101, 071905 (2012); http://dx.doi.org/10.1063/1.4747198 (4 pages) | Cited 1 time

Online Publication Date: 16 August 2012

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The α-Bi2O3 to δ-Bi2O3 phase transformation has been locally induced by laser irradiation in ceramic samples and single-crystal nanowires of this oxide. The threshold power densities necessary to induce this transformation, as well as the corresponding transformation kinetics and its temporal stability, have been investigated in both kinds of samples by micro-Raman spectroscopy. The appearance of the δ phase was also monitored by spatially resolved photoluminescence spectroscopy. An emission band peaked near 1.67 eV, not observed in α-Bi2O3, is tentatively attributed to δ-Bi2O3 near band gap transitions.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
78.67.Uh Nanowires
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
71.20.Nr Semiconductor compounds

Barocaloric effect in the magnetocaloric prototype Gd5Si2Ge2

Suheyla Yuce, Maria Barrio, Baris Emre, Enric Stern-Taulats, Antoni Planes, Josep-Lluís Tamarit, Yaroslav Mudryk, Karl A. Gschneidner, Jr., Vitalij K. Pecharsky, and Lluís Mañosa

Appl. Phys. Lett. 101, 071906 (2012); http://dx.doi.org/10.1063/1.4745920 (4 pages) | Cited 4 times

Online Publication Date: 16 August 2012

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We report on calorimetric measurements under hydrostatic pressure that enabled us to determine the barocaloric effect in Gd5Si2Ge2. The values for the entropy change for moderate pressures compare favourably to those corresponding to the magnetocaloric effect in this compound. Entropy data are complemented with direct measurements of the adiabatic pressure-induced temperature change.
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62.50.-p High-pressure effects in solids and liquids
65.40.gd Entropy
07.20.Fw Calorimeters
75.30.Sg Magnetocaloric effect, magnetic cooling
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