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1 Mar 2008

Volume 103, Issue 5, Articles (05xxxx)

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A study on bending direction of sheet metal in laser forming

Yongjun Shi, Yancong Liu, Zhenqiang Yao, and Hong Shen

J. Appl. Phys. 103, 053101 (2008); http://dx.doi.org/10.1063/1.2887995 (6 pages)

Online Publication Date: 3 March 2008

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Concave laser forming and convex forming are all required for the complicated curved surface plate forming. Concave laser forming can be readily obtained by temperature gradient mechanism, while convex forming may be achieved based on buckling mechanism. To achieve precise control of bending direction of plate, buckling critical condition is analyzed when the buckling mechanism plays a dominant role, and a judgment criterion of working conditions of buckling mechanism, Fbuckling value, is derived. To verify the validity of the Fbuckling value, the experiments and numerical simulations are carried out. The results suggest that the bending direction of the plate can be exactly judged according to the Fbuckling value. In addition, the effects of the heating location and starting point on the bending direction are discussed, which provide further insight into the convex forming process and is helpful for the parameter selection of future process planning.
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46.32.+x Static buckling and instability
46.35.+z Viscoelasticity, plasticity, viscoplasticity
81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains
79.20.Ds Laser-beam impact phenomena

Polarization selection with stacked hole array metamaterial

M. Beruete, M. Navarro-Cía, M. Sorolla, and I. Campillo

J. Appl. Phys. 103, 053102 (2008); http://dx.doi.org/10.1063/1.2841471 (4 pages) | Cited 11 times

Online Publication Date: 4 March 2008

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Polarization rotation or selection appears in materials with optical activity, or those with Faraday effect, or in liquid crystals. In this letter we present a structure, with an analogous response, using stacked extraordinary transmission subwavelength hole arrays modified to be nearly self-complementary. This produces a polarization selector because of the negative index of refraction for one of its linearly polarized eigenwaves. Simulation results and experiments at millimeter wavelengths confirm these features. Applications in miniaturized devices are envisioned as well as the possibility to scale to optical wavelengths.
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42.70.-a Optical materials
78.20.Ek Optical activity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ls Magneto-optical effects

Single mode photonic quantum ring laser fabricated in hyperboloid drum shape

Junho Yoon, Sung-Jae An, O’Dae Kwon, and Ja Kang Ku

J. Appl. Phys. 103, 053103 (2008); http://dx.doi.org/10.1063/1.2841418 (6 pages) | Cited 1 time

Online Publication Date: 5 March 2008

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From three dimensional whispering gallery cavities of GaAs photonic quantum ring fabricated in hyperboloid drum shape by chemically assisted ion beam etching with the central active region diameter of 0.9 μm, we have observed single mode lasing near 838 nm with a record low injection threshold of 300 nA (Jth = 47.1 A/cm2) in continuous wave operation at room temperature. This indicates that the quantum ring lasing phenomena associated with the three dimensional whispering gallery modes continue to persist, even at the submicron range overcoming the conventional two dimensional whispering gallery mode limit.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

High-resolution observations of an amorphous layer and subsurface damage formed by femtosecond laser irradiation of silicon

T. H. R. Crawford, J. Yamanaka, G. A. Botton, and H. K. Haugen

J. Appl. Phys. 103, 053104 (2008); http://dx.doi.org/10.1063/1.2885111 (7 pages) | Cited 11 times

Online Publication Date: 6 March 2008

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Using transmission electron microscopy (TEM), we observed the micro- and nanostructures of silicon after irradiation by ∼ 150 fs duration pulses centered at 800 nm wavelength. Specimens irradiated with a single pulse of 11 J/cm2 fluence and with five pulses, each with a fluence of 1.3 J/cm2, exhibited various structures which included amorphous phases. The amorphous phases were pure silicon, as was revealed by high-resolution TEM imaging, nanobeam diffraction patterns, high-angle annular dark-field images, conventional diffraction images, and energy-dispersive x-ray spectra. Irradiation with a single pulse of 1.5 J/cm2 produced neither amorphous material nor lattice defects. Single-pulse irradiation at a fluence of 33 J/cm2 and irradiation by four pulses at 11 J/cm2 led to substantial subsurface damage around the center of the laser spot. It is concluded that multiple-pulse irradiation produces crystallographic damage more readily than a single pulse.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.47.Fg Semiconductor surfaces
68.35.bj Amorphous semiconductors, glasses
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Focusing surface plasmons via changing the incident angle

Humeyra Caglayan, Irfan Bulu, and Ekmel Ozbay

J. Appl. Phys. 103, 053105 (2008); http://dx.doi.org/10.1063/1.2844552 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2008

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We report a circular metallic aperture with a subwavelength circular slit in the microwave regime, in which we experimentally demonstrate that this aperture can excite and focus surface plasmons. Under normal illumination, there is no focusing of the surface plasmons. However, by changing the incident angle, it is possible to focus surface plasmons. We showed that under a 20° illumination angle surface plasmons focus at 4 cm away from the center on the surface of the aperture.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Do the grain boundaries of β-In2S3 thin films have a role in sub-band-gap photosensitivity to 632.8 nm?

R. Jayakrishnan, Teny Theresa John, C. Sudha Kartha, K. P. Vijayakumar, Deepti Jain, L. S. Sharath Chandra, and V. Ganesan

J. Appl. Phys. 103, 053106 (2008); http://dx.doi.org/10.1063/1.2841488 (6 pages) | Cited 4 times

Online Publication Date: 10 March 2008

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Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532 nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8 nm. Photoresponse to excitation wavelength of 632.8 nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.
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68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
81.15.Rs Spray coating techniques
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.Mm Grain and twin boundaries
73.50.Pz Photoconduction and photovoltaic effects

A multiplexed fiber Bragg grating sensor for simultaneous salinity and temperature measurement

Liqiu Men, Ping Lu, and Qiying Chen

J. Appl. Phys. 103, 053107 (2008); http://dx.doi.org/10.1063/1.2890156 (7 pages) | Cited 17 times

Online Publication Date: 11 March 2008

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An in-line one-fiber approach to realize simultaneous measurement of salinity and temperature is proposed. The sensor system, which consists of multiplexed polymer-coated fiber Bragg gratings, showed that the polyimide-coated grating responds to variations of both temperature and salinity, while the acrylate-coated grating is only sensitive to the environmental temperature. The experimental results indicated that the temperature sensitivity of the acrylate-coated grating in water was 0.0102 nm/°C for redshifted Bragg wavelength with increasing temperature, and the temperature and the salinity sensitivities of the polyimide-coated grating were 0.0094 nm/°C (redshifted) and 0.0165 nm/M (blueshifted), respectively, which are in excellent agreement with the theoretical analysis.
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42.81.Pa Sensors, gyros
42.79.Dj Gratings
82.80.-d Chemical analysis and related physical methods of analysis

Calculated temperature rise in midinfrared laser irradiated Hg0.72Cd0.28Te

Asta Katrine Storeboe, Trond Brudevoll, and Knut Stenersen

J. Appl. Phys. 103, 053108 (2008); http://dx.doi.org/10.1063/1.2890751 (9 pages) | Cited 3 times

Online Publication Date: 11 March 2008

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We present results from a numerical study on heating in a 10 μm thick layer of Hg0.72Cd0.28Te induced by 1 μs long laser pulses at photon energies close to the band gap of the material. A number of highly nonlinear mechanisms contribute to the heating, their relative importance being dependent on laser wavelength, instantaneous irradiance, and material temperature. Mechanisms studied include one- and two-photon absorptions across the band gap, intervalence band absorption between light- and heavy hole bands, electron-hole recombination, free-carrier absorption, excess carrier temperatures, and refractive index changes. The increase in band gap with temperature eventually terminates one-photon absorption from the valence to the conduction band, and further heating is driven by much weaker absorption processes. The varying band gap also introduces changes in electron- and light hole masses and thereby in the separation between the light- and heavy hole bands, thus strongly affecting intervalence band absorption. At the shortest laser wavelength of 3.8 μm, the simulations indicate that surface melting will occur at fluence levels in the range of 2–3 J/cm2, while more than 10 J/cm2 will be required for melting at wavelengths beyond 5 μm.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.dj Melting of specific substances

Excitonic and pair-related photoluminescence in ZnSe nanowires

Ankur Saxena, Suxia Yang, U. Philipose, and Harry E. Ruda

J. Appl. Phys. 103, 053109 (2008); http://dx.doi.org/10.1063/1.2885729 (7 pages) | Cited 7 times

Online Publication Date: 11 March 2008

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It has been established that deviations from stoichiometry during the growth of ZnSe crystals result in point defects, which influence its electronic properties. We report on detailed photoluminescence results and their systematic analysis for ZnSe nanowires. We studied photoluminescence from vapor-phase grown undoped ZnSe nanowires grown under excess Zn conditions, and in particular the dependence on excitation intensity. Luminescence spectra were characterized by strong near-band-edge luminescence with negligible deep-level emission. We observed excitonic emission at 2.794 eV related to the neutral donor at VSe. The binding energy of the exciton was found to be 7 meV, and that of the donor was 35 meV. Two donor-acceptor pair transitions at 2.714 and 2.686 eV were also observed, which can be related to the defect complexes of native defects with other native defects or with common unintentional shallow donors and acceptors. The ionization energies of both donors were 27 meV, whereas those of the acceptors were 102 and 139 meV, respectively.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
71.55.Gs II-VI semiconductors
73.22.Lp Collective excitations
71.15.Nc Total energy and cohesive energy calculations

Direct observations for the superprism effect in photonic crystals utilizing negative refraction

S. Y. Yang, J. Y. Wu, H. E. Horng, Chin-Yih Hong, and H. C. Yang

J. Appl. Phys. 103, 053110 (2008); http://dx.doi.org/10.1063/1.2890390 (4 pages) | Cited 1 time

Online Publication Date: 14 March 2008

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In this work, we experimentally explored the negative-refraction superprism effect in photonic crystals by investigating the frequency-dependent negative refractive index of photonic crystals at microwave frequencies from 8.2 to 8.4 GHz. By detecting the spatially distributed intensity of a transmitted microwave whose incident angle is well controlled, we determined the propagating path, the refractive angle, and the refractive index of the transmitted microwave. The highly dispersive relationship between the negative refractive index and the frequency of microwave observed indicates potential applicability of this method for being used in a microwave wavelength demultiplexer by utilizing the negative-refraction superprism effect in photonic crystals.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.25.Gy Edge and boundary effects; reflection and refraction
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