1,720,966 research outputs found
Second-order optical nonlinearity induced in high-index bismuthate glass by thermal poling
No full textSecond-order optical nonlinearity was induced in Bi content was increased from 6.25 mol% to 25.0 mol%. The formation of the nonlinearity was found to depend critically on poling temperature and time, sample thickness and glass-electrode contact
Second-order nonlinearity profile in thermally poled twin-hole fibre
No full textThe second-order nonlinearity profile in thermally poled twin-hole fibre was characterized by second-harmonic scanning optical microscopy. The technique enabled us to optimize the poling parameters in order to obtain overlap between non-linear region and core
Dissolution of embedded gold nanoparticles in sol-gel glass film
No full textMaterials with metallic nanoparticles are widely investigated in order to fabricate plasmonic devices, for which the control of the material properties is required. A simple way to control the metal surface plasmon resonance in selected regions of the material is to dissolve the embedded metallic nanoparticles by means of d.c. electric field. Dissolution of embedded silver and copper nanoparticles has been demonstrated recently through poling-assisted bleaching of Ag-doped and Cu-doped nanocomposite glasses, respectively. The next challenge is the dissolution of other metallic nanoparticles, such as gold, which are more difficult to ionize. Here, we demonstrate the dissolution of gold nanoparticles (15 nm in diameter) by d.c. electric field thanks to a novel material design in which the nanoparticles were embedded in a high resistivity sol-gel film on top of a soda-lime-silicate glass substrate with a higher conductivity compared to the film. The role of the film resistivity is made obvious by studying two different film compositions. This result brings about the possibility to use other metallic nanoparticles for tailoring the region of transparency of glasses and opens perspectives for the fabrication of new plasmonic devices
Origin and enhancement of the second-order non-linear optical susceptibility induced in bismuth borate glasses by thermal poling
No full textThe second-order non-linear optical susceptibility of thermally poled glasses, χ(2), should be enhanced in proportion to the intrinsic third-order susceptibility χ(3), for a given frozen-in electric field (i.e. χ(2) = 3Edcχ(3)). In order to test this prediction, bismuth-borate (Bi2O3–ZnO–B2O3) glasses, for which χ(3) increased with increasing Bi2O3 content, were thermally poled and the second-order non-linear coefficient was determined. Poling conditions and current dynamics turned out to be very different from those in silica. Poling temperatures had to be relatively close to glass transition temperatures and the glass–electrode contact had to be intimate in order to induce the non-linearity which was located in a near-surface layer at the anode side. A poling mechanism was proposed which relied on proton migration, took into account ion injection and glass ionization, and was able to explain most of the experimental results. The χ(2) values increased with increasing χ(3) as predicted but did not exceed 0.7 pm/V. By comparison with silica, it was inferred that the dielectric breakdown strength Eb was lower in bismuth borate and decreased with increasing Bi2O3 content. This latter result demonstrated the importance to select glass compositions on the basis of both χ(3) and Eb for the purpose of enhancing χ(2)
2pm/V in poled Bismuth-Zinc-Borate high index glass
Full text linkThermal poling freezes an intense static electric field (Edc) in glass resulting in a permanent second-order nonlinearity via a rectification process: χ(2) = 3χ(3)Edc. The low third-order nonlinearity limits the χ(2) of silica glass to 0.7 pm/V. Hence, poling of high χ(3) glasses offers an attractive route towards glass based integrated electro-optical modulators and frequency converters for which χ(2) of the order of 5 pm/V or higher would be desirabl
All-fibre frequency conversion in long periodically poled silica fibres
No full textEfficient all-fibre frequency doubling of 1.5 µm pulsed fibre laser has been demonstrated. 3.6 mW of second-harmonic light in fundamental mode was produced by quasi-phase-matching in a 11.5 cm long periodically poled germanosilicate fibre. The χ(2)-grating was fabricated by continuous periodic-UV-erasure
The problem of achieving high second-order nonlinearities in glasses: The role of electric conductivity in poling of high index glasses
No full textEfficient thermal poling of electronically conducting glass is prevented by the inherent difficulty to record a large electrostatic field within such glasses. To overcome this limitation, a waveguide/substrate configuration has been proposed, in which the glass for poling was deposited as a film of appropriate thickness on a substrate chosen for its higher ionic conductivity. Owing to this configuration, the poling voltage drops entirely across the glass film, allowing high electrostatic field to be recorded in spite of the high electronic conductivity of the glass. The proposed method was demonstrated here in the case of bismuth-zinc-borate glasses, which possess high potential for poling because of their high intrinsic χ(3). A four-fold enhancement of χ(2) compared to bulk glass, from ~ 0.5 to ~ 2 pm/V, is demonstrated. It is also shown that the χ(2) values obtained are the highest sustainable by the glass limited by the onset of nonlinear conductivity. The waveguide/substrate configuration intrinsically allows obtaining perfect overlap of the poling induced second-order nonlinearity with the guiding region of the waveguide. An equivalent RC-circuit model describing the poled glass reveals that the value of the poling-induced second-order nonlinearity is strongly dependent on the ratio β between ionic and electronic conductivity. The most promising glass systems for poling are found to be the ones displaying the highest product χ(3)β. This work is performed on bismuth-zinc-borate heavy metal oxide glasses but the waveguide/substrate configuration proposed here is likely to be equally successful in enhancing the second-order nonlinearity in high χ(3) electronic conducting glasses such as for example telluride and chalcogenide glasses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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