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Fabrication of structured GLS-Se glass preforms for fibre drawing
No full textGallium lanthanum sulfide (GLS) with the addition of selenium (Se) glasses, have been proven as a reliable medium to transmit light in the range from the visible to the longwave infrared (LWIR). This family of chalcogenide glasses offer a broad transparency window depending on the composition. Their optical, mechanical and thermal properties have been exploited in their bulk form. Increasing interest in chalcogenide photonics research includes sensing for the civil, medical and military areas, as the molecular fingerprint region is within the GLS-Se glass transmission window. These application areas exploit the GLS-Se characteristics in an optical fibre geometry. The aim of this work was to explore the feasibility of obtaining glass rods and structured preforms from GLS-Se glass that could be drawn into optical fibres. For this, the extrusion process is explored by emphasizing the need to maintain the desirable glass characteristics throughout the entire process, from the glass melting to the fibre drawing. For this purpose, each step was studied and defined to maximise the exploitation of the equipment and the materials involved. For the first time it is shown that GLS-Se glasses can be extruded with a minimum alteration of their optical, thermal and mechanical properties. The amorphous phase was maintained, and corroborated by refractive index measurements, Raman spectroscopy and XRD. Several challenges were arisen during this work, using each of them to fully complete and develop a methodology to be able to obtain optical fibres. Further work might include reducing the losses of the optical fibres using this process
Manufacturing of GLS-Se glass rods and structured preforms by extrusion for optical fiber drawing for the IR region
No full textChalcogenide glasses are amorphous solid materials formed from chalcogen elements bonding with metals to form typically in binary or tertiary compounds. One family of chalcogenide glasses, based on gallium and lanthanum sulphides, possesses properties important for the infrared (IR) window transmissions and IR applications; these include thermal stability, high solubility of rare earth ions, low phonon energy and high laser damage threshold. Efforts have been made to produce new chalcogenide glasses that can extend the IR transmission window further into the IR. Work has led to the successful melting of a selenium-modified gallium lanthanum sulphide (GLS-Se) glass that can transmit up to 15 μm, however these glasses have, to date, only been demonstrated in bulk glass form. We aim to develop processes for the fabrication of chalcogenide optical fiber to exploit the properties of chalcogenide glasses. Several potential applications include sensing for the civil, medical, and military areas, as these materials offer transmission over much of the molecular fingerprint region (2 to 25 μm). The aim of our work is to understand and control the thermal properties and stability of GLS-Se glasses without compromising their optical properties, in order to produce transparent glass rods and demonstrate the feasibility in fabrication for structured optical preforms by extrusion, as the first step to achieve optical fiber from GLS-Se glass.</p
Fabrication of structured GLS-Se glass preforms by extrusion for fibre drawing
No full textChalcogenide glasses due to their low phonon energy and high ion solubility, make them an ideal candidate for active and passive fibres for infrared applications. Co-extrusion process for structured preform fabrication is explored
Chalcogenide optical fibres based on gallium lanthanum sulphide-Se for passive and active applications
No full textChalcogenide optical fibres contain mixtures of chalcogen elements (i.e. S, Se and Te) bonded covalently to other metallic elements that facilitate a stable glass formation. Our work in particular focuses on chalcogenide glasses containing a high proportion of lanthanum, that is gallium lanthanum sulphide glasses (GLS). These glasses due to their nature are characterized by a range of desirable properties such as chemical durability, host for rare-earth (RE) ions, low thermal expansion, high laser damage threshold, density and refractive index and a good transparency in the infrared (IR) region. Characteristics that are beneficial for active and passive applications such as sensors or high-energy IR laser power delivery, as examples. To increase the IR transmission window of GLS glasses a new family of chalcogenides have been developed, incremental additions of Se to the GLS glasses have proved their value to improve the transmission spectrum from visible to Long Wavelength Infrared (LWIR) range up to 15μm, depending on the composition. The strong thermal and mechanical characteristics of GLS-Se glasses compared to GLS have also shown that they can suit the production of optical elements, such as optical fibres that require certain thermal and mechanical stability for fibre drawing to avoid crystallization and breakages. [1-5] Theoretical minimum loss predictions in GLS based optical fibres have shown up to 0.5 dB km-1 at 3.5 μm, used in thermal imaging, unfortunately we are still far from that value but big efforts are being made to improve the production of optical fibres as shown in Fig. 1 by obtaining novel processes and more pure raw materials. [6] Chalcogenide RE doped glasses have demonstrated laser action, showing that they are suitable for active applications such as optical amplifiers and lasers [7]. The aim of this research is to join the well-known properties of chalcogenides glasses for the IR region with the development of a novel process to obtain functional passive and active optical fibres and prove the reliability as a host for RE ions, future work will include laser demonstration
GLS-Se optical fibre from extruded glass structured preforms and rods for the IR region
No full textDepending on composition, chalcogenide glasses have been proven as a reliable medium to transmit light in the range from the visible to the long-wave infrared (LWIR), specialty glasses based on gallium lanthanum sulfide (GLS) with a selenium (Se) addition. This family of glasses offers a broad transparency window depending on the composition. Their optical, mechanical, and thermal properties have been exploited in their bulk form. In this paper, we demonstrate the fabrication of optical fibres from extruded structured (core-clad) preforms and rods, with an emphasis on maintaining the intrinsic characteristics of the glass and exploiting the optical fibre geometry for light delivery
Chalcogenide materials: Novel compositions and new applications
No full textIn this talk, we describe our recent work on selenium modified Ga:La:S glasses. The addition of Se improves the infrared transmission sufficiently to capture enough of the 8-12 micron window to allow thermal imaging, while at the same time, allowing sufficient visible transmission for object recognition using conventional image capturing. The addition of Se has other implications, increasing the optical nonlinearity, providing longer fluorescent lifetimes when doped with rare earth ions and expanding the transmission window in the important 3-5 micron region. Ga:La:S glasses are superior to commercially available chalcogenides based on alloys of Ga and/or As with S, Se and/or Te. They offer significantly higher alkaline resistance, greater mechanical strength and over 300ºC higher working temperature (Tg > 500ºC). All of these new features suggest Ga:La:S-Se may be a material suitable for the next generation of mid-IR sources through supercontinuum or rare earth doping
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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