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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The third harmonic generation of light (266 nm) is enhanced, sensitively depending on the time delay between a pair of pulses split from a single 800 nm femtosecond laser pulse, when they are focused and collided in air. This finding offers a convenient and widely applicable technique to detect temporal and spatial overlapping of two femtosecond pulses. This technique has several advantages over the conventional sum frequency generation method using nonlinear optical crystals, since it obviates the need for expensive crystals, free from phase matching, and elimination of temporal walk off. By applying it to "a holographic encoding system using an interference femtosecond laser pulse," a periodic fringe spacing is minimized to ∼430 nm by extending the colliding angle between two-pulse beams up to ∼160 °C. © 2002 American Institute of Physics.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion implantation induced dc electrical conductivity changes in polycrystalline WO3 thin films was examined. Helium, argon, and tungsten ions were implanted under the following conditions: helium at 90 keV, argon at 360 keV, and tungsten at 300 keV. The fluence range studied was from 1×1017 to 3×1017 cm−2 for helium and argon, and from 5×1014 to 5×1015 cm−2 for tungsten. The 300 K conductivities after implantation at a 1×1017 cm−2 fluence increased from ∼10−5 to ∼10−1 S cm−1 for helium implantation and to ∼102 S cm−1 for argon implantation. Also, implantation induced a broad optical absorption feature at ∼1000 nm and a negative thermopower coefficient indicating n-type conduction. The implanted samples exhibited low conductivity activation energies, which were consistent with degenerate conduction. Tungsten implantation induced conductivities were higher than those resulting from either helium or argon implantation as a conductivity of ∼102 S cm−1 was obtained at a 5×1015 cm−2 fluence. These conductivity changes are correlated to the displacements per atom resulting from the various ion implantations. Several mechanisms are responsible for the observed donor species increase: (1) in the proton case the implanted species becomes a donor, (2) in the helium and argon cases a charged oxygen vacancy may be formed by the nuclear collisions that occur during implantation, and (3) in the tungsten case the subsequent oxidation of the implanted tungsten results in the formation of a donor species. © 1998 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It was reported [H. Hosono et al., Appl. Phys. Lett. 65, 1632 (1994)] that nanometer-sized crystalline (nc) Ge colloid particles were formed by implantation of protons into 0.1 GeO2–0.9 SiO2 glasses at room temperature. The depth profiles of Ge colloids and the density of Si–OH or Ge–OH created by the implantation were measured and compared with those of energy deposition in order to examine the formation mechanism of Ge colloids by proton implantation. The depth region of nc-Ge particles was found to correspond to the overlapped region between the OH distribution and the peak of electronic energy deposition. Transmission electron microscopic observation revealed that the size of Ge colloid particles created by proton implantation was close to that of GeO2-rich particles occurring in the substrate glasses. These results indicate that GeO2-rich particles are converted into Ge particles by a combined effect of the electronic excitation and the chemical reaction of implanted protons. A mechanism was proposed consisting of displacement of bridging oxygen into interstitials by electronic excitation and subsequent trapping of the oxygen interstitials by a formation of OH groups. © 1997 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fast proton conducting glasses have been obtained in Mg(PO3)2 glasses by implantation of protons at 120 keV to a fluence of 1×1018 cm−2. The dc conductivity and the activation energy of the conduction in the implanted glasses are 5×10−4 s cm−1 at room temperature and 0.18 eV, respectively. No fast proton conduction was observed for H+-implanted SiO2 and Ca(PO3)2 glasses. Infrared absorption spectra revealed that implanted protons are present in the form of X–OH (X=Si or P) in SiO2 and Ca(PO3)2 glasses implanted with H+ ions to 1×1018 cm−2, but exist as POH groups and molecular water H2O in Mg(PO3)2 glasses. A quantitative discussion on the proton conductivity led to the conclusion that the coexistence of acidic groups such as POH and molecular water H2O is a structural requirement for the emergence of fast proton conduction in oxide glasses. The formation of H2O in Mg(PO3)2 was understood by considering its thermodynamic stability over SiO2 and Ca(PO3)2 glasses. © 1997 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1357-1363 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanometer-sized crystalline Ge colloid particles in 9SiO2–1GeO2 glasses were formed by implantation of protons at 1.5 MeV without post-thermal annealing. Although oxygen-deficient type point defects associated with Ge ions were primarily formed to fluences (approximately-less-than)1×1017 cm−2, the formation of Ge fine crystalline particles was observed for fluences (approximately-greater-than)5×1017 cm−2. No formation of Ge colloids and the Ge-related point defects were noted for implantation of 1.5 MeV He+ to a fluence of 1×1018 cm−2. The depth of Ge colloid formation layers was 22–26 μm from the implanted surface. This depth region agreed well with the peak region of electronic energy deposition. Ge–OH groups were formed preferentially over Si–OH groups upon implantation of protons and the decay curve upon isochronal annealing was close to that of the optical absorption at ∼3 eV, which was attributed to nanometer-sized Ge. A red photoluminescence peaking at ∼1.9 eV was observed for all the implanted substrates. A tentative formation mechanism of Ge colloids in these glasses was proposed. © 1996 American Institute of Physics.
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fine-pitched micrograting structures were holographically encoded in amorphous (a-) SiO2 thin films on silicon wafers by colliding a pair of focused pulses split from a single, mode-locked Ti: sapphire, femtosecond laser. A method enhancing the third-harmonic generation resulting from the nonlinearity of air adjusted the optical paths of the two pulses. Surface-relief-type gratings were formed on SiO2 glasses due to laser ablation when the laser power exceeded more than 0.3 mJ/pulse, while shallow grating structures were imprinted on a-SiO2 thin films by volume compaction (∼3%) when the irradiation power was reduced to ∼50 μJ/pulse. The postirradiation deepening of the valley of the grating structure was possible with chemical etching. The minimal spacing of 430 nm was encoded using the 800 nm laser. © 2001 American Institute of Physics.
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  • 7
    ISSN: 1436-2813
    Keywords: Key Words: renin-producing adrenal tumor ; extrarenal renin-producing tumor ; plasma renin activity ; immunohistochemical staining for renin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 1137-1139 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Refractive-index-modulated volume-type gratings were holographically encoded inside pure SiO2 glass plates by a single chirped (0.5–5 ps duration) laser pulse generated from a mode-locked Ti:sapphire laser (wavelength ∼800 nm, emission pulse duration ∼100 fs). Scanning-electron- and confocal-optical-microscopic observations revealed that microgratings were formed inside the sample at a depth of ∼5 mm from the top surface. Also, inside the SiO2 glass, three-dimensional periodic arrays of the grating and crossed-grating structures were fabricated. The present technique is a fast method that is applicable not only for encoding volume-type gratings inside all nonphotosensitive transparent dielectric materials, but also for fabricating optical devices such as distributed-feedback lasers and multilayered memories. © 2002 American Institute of Physics.
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  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two cross-superposed holographic gratings were encoded on silica glass by femtosecond laser pulses (wavelength ∼800 nm). A variety of periodic nanostructures from a one-dimensional wire array to two-dimensional arrays of holes or islands were formed by changing the energy density and the incidence angle of the irradiation laser beams. The smallest dimensions were a width of ∼15 nm for wires and a diameter of ∼20 nm for holes. Laser-driven microexplosions occurring within the microcylindrical-lens array created by the first laser pulse are suggested as a mechanism for the formation of these structures. Only two pulses are required to encode these periodic structures, which are applicable to emerging nanostructured devices such as photonic crystals and quantum dot or wire arrays. © 2001 American Institute of Physics.
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An ultraviolet light-emitting diode (LED) operating at room temperature was realized using a p–n heterojunction composed of transparent conductive oxides, p-SrCu2O2 and n-ZnO. Multilayered films prepared by a pulsed-laser deposition technique were processed by conventional photolithography with the aid of reactive ion etching to fabricate the LED device. A rather sharp emission band centered at 382 nm was generated when a forward bias voltage exceeding the turn-on voltage of 3 V was applied to the junction. The emission may be attributed to a transition associated with the electron–hole plasma of ZnO. © 2000 American Institute of Physics.
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