1,720,970 research outputs found
Near-infrared luminescence and single-mode laser emission from Nd<sup>3+</sup> doped compound glass and glass microsphere
No full textIn this letter, an Nd3+-doped compound fluorosilicate glass was successfully fabricated with the method of melt-quenching. Under the excitation of a 808 nm laser, enhanced near-infrared photoluminescence emission at the range from 1,065 to 1,140 nm was observed in the glass sample. To characterize its stability and resistance to environmental effects, transmission spectra at the range of NIR-MIR were measured under different environments, including humidity and temperature. In addition, the obtained fluorosilicate glass was also developed as a microsphere resonator by using CO2 laser heating method. When the diameter of the microsphere was controlled at 61.5 µm, coupling with a tapered fiber, single-multimode lasing in the wavelength range ~1,056–1,071 nm was achieved with a low lasing threshold of 1.5 mW. Compared to silica and phosphate glasses, this fluorosilicate glasses have lower phonon energy, which can reduce the probability of non-radiative transitions and improve the photoluminescence efficiency. Therefore, using it as the raw material, the developed microsphere resonator offers a high transition temperature and with a low lasing threshold, which are promising it for high performance sensing and detection applications
Effect of Tm<sup>3+</sup> concentration on the emission wavelength shift in Tm<sup>3+</sup>-doped silica microsphere lasers
No full textIn this work, a Tm3-doped solgel silica microsphere lasing at 2.0 μm is reported. Microspheres with different Tm3 concentrations are fabricated by overlaying different Tm3 concentration solgel solutions on the surface of a pure silica microsphere resonator and then annealing the sample with a CO2 laser. Based on a traditional fiber taper–microsphere coupling method, single and multimode microsphere lasing in the wavelength range 1.8–2.0 μm is observed if an 808 nm laser diode is used as a pump source. A relatively low threshold pumping power of 1.2 mW is achieved using this arrangement. This solgel method allows for an easy varying of the Tm3 doping concentration. The observed laser output shifts to longer wavelengths when the Tm3 doping concentration increases. This has been explained by the larger Tm absorption at shorter wavelengths. The ability to fabricate solgel co-doped silica glass microlasers represents a new generation of low threshold and compact infrared laser sources for use as miniaturized photonic components for a wide range of applications, including gas sensing and medical surgery.</p
Infrared-laser and upconversion luminescence in Ho<sup>3+</sup>-Yb<sup>3+</sup> codoped tellurite glass microsphere
No full textIn this letter, Ho3+-Yb3+ codoped tellurite glasses were fabricated using the melting-quenching method to produce optical microsphere cavities. A 980 nm excitation laser was coupled into the microsphere through a fiber taper, providing lasing at around 2.0 μm and upconversion luminescence in the visible (380-780 nm)
Tm<sup>3+</sup>-doped fluorotellurite glass microsphere resonator laser at 2.3 μm
No full textIn this Letter, we report lasing at 2.3 μm in Tm3+-single-doped and Tm3+=Ho3+-codoped fluorotellurite glass microsphere resonators. By employing a 793 nm diode laser as a pump and exploiting whispering gallery mode microresonators (WGMRs), dual-wavelength lasing at 1.9 and 2.3μm and triple-wavelength lasing at 1.9, 2.07, and 2.3μm are achieved in Tm3+-doped and Tm3+=Ho3+-codoped microspheres, respectively. The introduction of Ho3+ ions significantly reduces the lasing threshold of Tm3+ at 2.3 μm because of energy transfer.</p
3.9 µm emission in Nd<sup>3+</sup> sensitized Ho<sup>3+</sup> doped fluoroaluminate glasses
No full textHo3+ and Nd3+/Ho3+ doped fluoroaluminate glass samples were fabricated by the melt-quenching method and showed high transmittance and a wide transparency window. Under 808 nm pumping, emission at 3.9 µm, corresponding to the Ho: 5I5→5I6 transition, was observed. The presence of Nd3+ strongly enhances the Ho3+ emission. The emission and absorption cross-sections were calculated using the Judd-Ofelt, Füchtbauer-Ladenburg and McCumber theories and the energy transfer mechanism between Nd3+ and Ho3+ was analyzed. The most efficient 3.9 µm emission was obtained when the concentration ratio of Nd3+: Ho3+ is 1:2
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
