186,550 research outputs found
Spectroscopy of yttria-alumina-silica glass doped with thulium and erbium
No full textYttria-alumina-silica (YAS) glasses doped with Er3+ and Tm3+ have been examined spectroscopically for their prospect as fibre amplifier gain media for optical telecommunication systems. Absorption and emission spectra, as well as emission lifetime measurements and Judd-Ofelt calculations are reported. Tm3+:YAS glass has a emission bandwidth of 122nm around 1470nm, making it promising for S+ band amplification
Spectroscopy of Tm<sup>3+</sup>-doped yttrium-aluminosilicate glass
No full textResearch into Tm3+-doped glasses as gain media for optical amplifiers in the telecommunications S-band has been focused on glasses with low phonon energy like tellurite and fluoride glasses, because the high phonon energy of silicate glasses precludes emission around 1470nm. Glasses in the Y2O3 - Al2O3 - SiO2 (YAS) system have, despite their silica content, a maximum phonon energy of about 950cm-1, as well as good transparency and thermal stability. We report preliminary spectroscopy on Tm3+:YAS glass which highlights their potential as S-band amplifier gain media
Konradus Jander. Oratorum et rhetor um graecorum fragmenta nuper reperta
No full textPuech Aimé. Konradus Jander. Oratorum et rhetor um graecorum fragmenta nuper reperta. In: Revue des Études Grecques, tome 27, fascicule 123-124,1914. p. 343
Efficient Er:YAG lased pumped in-band by an Er/Yb fibre laser
No full textSolid-state lasers operating in the eye-safe wavelength regime around ~1.5-2.1 µm regime have numerous applications. In many of these applications the requirement for high- power is also accompanied by the need for high efficiency and good beam quality, which are often difficult to achieve in conventional solid-state lasers due to the detrimental effects of thermal loading. Recently, there has been dramatic progress in scaling output power from cladding-pumped Er/Yb and Tm doped silica fibre lasers operating in the 1.53-1.62 µm and 1.85-2.1 µm regime respectively. Fibre lasers offer the attraction of relatively simple thermal management and hence a high degree of immunity to thermal effects, but suffer from the drawback that, in pulsed mode, energies are limited by amplified spontaneous emission and by damage to the fibre end facets. An alternative approach which circumvents this problem is to use employ a hybrid laser approach where the cladding-pumped fibre laser is used to 'in-band' pump a bulk solid-state laser. This has the attraction of very low quantum defect heating in the bulk crystal and hence relatively weak thermal effects. In recent work, efficient operation of Er:YAG [1] and Ho:YAG [2] lasers, end-pumped by cladding-pumped Er/Yb and Tm fibre lasers respectively, has been demonstrated. cont'
High power Er:YAG laser at 1646nm pumped by an Er/Yb fibre laser
No full textSolid-state lasers operating in the eye-safe wavelength regime around ~1.5-2.1 µm regime have numerous applications. For many applications, the requirement for high power is accompanied by the need for high efficiency and good beam quality, which are difficult to achieve in conventional solid- state lasers because of thermal effects. Fibre lasers are less affected by thermal effects, but pulse energies are limited by amplified spontaneous emission and by damage to the fibre end facets. An alternative approach which circumvents this problem is to use a hybrid laser where a fibre laser is used to 'in-band' pump a bulk solid-state laser. In this paper we describe an Er:YAG laser pumped by a tunable, cladding-pumped Er/Yb fibre laser and discuss factors affecting the laser performance. Five crystals with Er-concentrations in the range 0.25% to 4 at% and with crystal lengths selected for ~95% absorption of the pump light at 1532nm were used, and the laser performance was investigated for a range of output coupler transmissions (2-30%) at 1646nm. In preliminary experiments we have achieved a maximum output power of 4W at 1646nm for 11W of absorbed pump power corresponding to an efficiency of 36%, using a crystal with 0.5 at% Er-concentration and an output coupler transmission of 10%. Our experiments have revealed that the cw efficiency decreases quite markedly for higher Er-concentrations. The origin this behaviour is the subject of further investigation and our findings will be presented. The prospects for further increase in output power and efficiency will also be discussed
High power and ultra efficient operation of 1645 nm Er:YAG laser pumped by a 100W tunable Er/Yb fiber laser
No full textAn Er:YAG laser, end-pumped by a cladding-pumped 100W tunable Er,Yb fiber laser, has yielded 60W of continuous-wave output at 1645nm at room-temperature for 82W of incident pump power at 1532nm. The corresponding slope efficiency was 80.7%
Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics
No full textTransparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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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