1,720,964 research outputs found
Quantum efficiency measurements in oxygen-containing gallium lanthanum sulphide glasses and fibers doped with Pr<sup>3+</sup>
No full textThe quantum efficiency of Pr3+ emission at 1.3µm from the 1G4 - 3H5 transition is measured in Gallium Lanthanum Sulphide (GLS) glass containing varying quantities of lanthanum oxide. The variation of quantum efficiency with host composition is described, and the variation of quantum efficiency with pump wavelength in oxide-containing hosts is compared to a model of the effect of the addition of oxygen on the spectroscopy of the Pr ion. Oxide-containing GLS glasses can show quantum efficiencies of up to 84% of that of pure GLS, while retaining considerably better thermal and glass-forming properties. No degradation of quantum efficiency is seen when GLS glass is pulled into fiber form
Multiphonon decay rates in chalcogenide glasses
No full textThe optical properties of rare earth doped chalcogenide glasses have received a considerable amount of interest in recent years, primarily because of their very low multiphonon decay rates when compared with other glass hosts. In this paper we compare the measured multiphonon decay rates for rare earth doped gallium lanthanum sulphide (GaLaS) glass with results obtained previously and find significant discrepancies. Our results indicate that the multiphonon decay rate across energy gaps in the range 2000-3500/cm is considerably lower than previously calculated and we provide a more accurate set of parameters to describe this process in rare earth doped chalcogenide glasses. These results have significant implications for active devices applications operating in the important 3-5µm wavelength range, where the multiphonon decay rate appears almost an order of magnitude lower than previously estimated
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Halide-modified Ga-La sulfide glasses with improved fibre-drawing and optical properties for Pr<sup>3+</sup>-doped fibre amplifiers at 1.3µm
No full textWe report Cs halide-modified Ga-La sulfide glasses, a new class of chalcohalide glasses with improved fiber-drawing and optical properties suitable for Pr3+-doped fiber amplifiers at 1.3µm. Cs halide-modified Ga-La sulfide glasses retain the essential characteristics of low phonon-energy and good rare-earth solubility of pure Ga-La sulfide glasses. However, they transmit further into the UV/visible region of the spectrum, and can meet the need of high thermal stability for fiber fabrication
Infrared emission and ion-ion interactions in thulium and terbium doped gallium lanthanum sulphide glass
No full textInfrared emission at 0.7, 0.8, 1.2, 1.5, 1.8, 2.3, 3.8, and 4.8µm is measured in thulium (Tm3+) and terbium (Tb3+) doped gallium lanthanum sulphide (GLS) glass. Emission cross sections are calculated from the absorption and emission spectra using Judd-Ofelt analysis, the Füchtbauer-Ladenburg equation, and the theory of McCumber. Fluorescence and lifetime measurements confirm energy transfer from Tm3+ to Tb3+ ions and reveal a number of new cross-relaxation/upconversion processes between Tm3+ ions involving the 3F2,3 and 3H5 levels that can only be observed in low phonon energy materials. These processes indicate that the most efficient pump wavelength for the 1.2µm and 3.8µm transitions is 0.7µm. The Tm3+ fluorescence at 3.8µm coincides with an atmospheric transmission window and the Tb3+ fluorescence at 4.8µm overlaps with the fundamental absorption of carbon monoxide, making the glass a potential fibre laser source for remote sensing and gas sensing applications
Variations on the Author
Get PDF“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
Spectroscopy and quantum efficiency of halide-modified gallium-lanthanum sulphide glasses doped with praseodymium
No full textThe production of competitive fibre amplifiers in the 1.3µm region requires both good quantum efficiency in the lasing ion and the capability to produce low-loss fibers. Alkali metal halide substituted gallium lanthanum sulphide (GLS) doped with Pr3+ may provide a route to both. We describe measurements of the optical spectroscopy and radiative quantum efficiency (RQE) of Pr3+ emission at 1.3µm from the 1G4 - 3H5 transition in GLS glass containing CsCl, CsI and RbCl. The results indicate that CsCl-containing GLS glasses. which have better thermal and glass-forming properties than pure GLS, can show quantum efficiencies of up to ~80% of that of pure GLS and thus are good candidates for 1.3µm fiber amplifiers
Optical measurement of narrow band rare-earth 4f levels with energies greater than the bandgap of the host
No full textExcited-state absorption spectra of erbium and thulium doped gallium lanthanum sulphide glasses reveal transitions whose final 4f states do not appear in the ground state absorption spectra due to resonance with the fundamental absorption of the glass host. The results give direct evidence for the model of isolated rare earth ions with highly shielded 4f levels showing no noticeable interaction with the host material despite resonance. Only the energy splitting of the 4f levels is relevant for energy transfer processes between rare-earth ions and the host material whereas the absolute energetic position is unimportant
Visible upconversion in rare-earth doped gallium lanthanum sulphide based glasses
No full textChalcogenide glasses are usually known for their good infrared and poor visible transparency which limit their applications to passive and active devices in the infrared wavelength region. Gallium lanthanum sulphide glasses, however, show visible transparency down to 500nm. The low phonon energy of the glass increases the radiative quantum efficiency of rare-earth energy levels compared to commonly used fluorozirconate glasses and provides long-lived intermediate levels for efficient two-step excitation to visible energy levels. Green and red upconversion emission has been observed in Pr3+, Nd3+, Ho3+, and Er3+ doped glasses under Ti:sapphire pumping in wavelengths regions where diode laser sources are easily available. Lifetime measurements reveal the excitation process is either excited-state absorption or upconversion caused by ion-ion interactions. Modification of the glass with lanthanum oxide or caesium chloride improves the visible transparency and shifts the UV absorption edge to 450nm and 400nm, respectively, and also improves the fibre drawing of these glasses
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