1,720,967 research outputs found
Time resolved and site-selective spectroscopy of thulium- doped into germano- and alumino-silicate optical fibres and preforms
No full textOptical properties of thulium ions doped in varying concentrations into germano- and alumino-silicate glass fibres and their preforms are studied. Absorption and fluorescence spectra are shown to vary little with thulium concentrations up to 12000 ppm. but vary drastically with germanium or aluminium codopant. Resonant fluorescence studies of Tm3+ show correlations in the movements of the Stark levels of the ground state, indicating systematic correlations between the ion site and Stark level position. An upper limit of 10 /cm for the homogeneous line width of thulium in alumino-silicate glass is established at 9 K. The lifetimes of the 1G4 and 3F4 levels are studied and are related to codopant influence and cross-relaxation which are linked to fibre drawing and Tm3+- concentration. A significant lifetime shortening is observed on drawing preform to fibre. A model is presented for non-exponential decay of the 3F4 level. Three- and four-level rate equations have been successfully used to simulate the observed rise of the 3F4 fluorescence and decay of the 1D2 fluorescence, excited resonantly and by up-conversion processes, respectively. These models yield both the excitation pump rate and cross-relaxation rates
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
Fabrication and characterisation of reverse proton exchange optical waveguides in Neodymium doped lithium niobate crystals
No full textIn this work, the complete fabrication process which combines Proton Exchange (PE) and Reverse Proton Exchange (RPE) in Neodymium doped LiNbO3 channel waveguides is reported. To produce the PE-RPE channel waveguides the fabrication of dielectric SiO2 masks had to be implemented. For this propose, we adopted a technique based on the Ion Plating Plasma Assisted Deposition of SiO2 followed by the standard ultraviolet photolithographic patterning. On the other hand, we determined the main optical and spectroscopic properties of Nd3+ ions in the channel waveguides including the study of the lifetime as function as the polarisation
Correlation between compositional and refractive index profiles in LiNbO3 : Zn diffused optical waveguides
No full textWaveguides fabrication in Z- and X-cut LiNbO3 crystals by vapor zinc diffusion has been studied by secondary ion mass spectrometry and optical measurements. Compositional analysis of diffused substrates shows the formation of a Zn rich superficial layer, followed by a deeper region with decreasing Zn concentration. A subsequent thermal annealing process has been performed to let zinc ions further diffuse into the substrates. The composition profiles have been correlated with the refractive index profiles, reconstructed by optical reflectivity measurements. The results and the nature of the detected layers are discussed and correlated with previous x-ray studies obtained in the same samples
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dual-polarization-pump CW laser operation in Nd3+:LiNbO3 channel waveguides fabricated by reverse proton exchange
No full textIn this work, continuous-wave laser action at 1084.5 nm at room temperature in LiNbO3:Nd3+ channel waveguides, fabricated by reverse proton exchange (RPE), is reported. The sample was pumped at k = 808 nm in either s or p-polarized configurations, TE and TM-pumping schemes, being the laser emission p-polarized at all power levels. The laser characteristics, as function of the pumping scheme (TE or TM), have been obtained. In both cases, the laser emission was stable, without any reduction in the output power even under continuous pump operation at maximum power at room temperature, indicating high resistance to photorefractive damage
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