543 research outputs found
An investigation of novel materials for active optical devices
No full textThe potential of a number of doped materials as amplifiers for optical communication has been assessed. This work focuses on transparent glass-ceramics as novel hybrid materials of glasses and crystals. Glass-ceramics comprising of LaF3 crystals in an aluminosilicate glass matrix, doped with Er3+, Pr3+ and Tm3+ have been prepared and characterized. Spectroscopy of these glass-ceramics is focused on the distribution of the dopant ions between the crystals and the residual glass. A novel method to calculate the ion distribution, based on fluorescence lifetime measurements, is developed and applied to both Er3+ and Pr3+ doped glass-ceramics. In the case of Er3+, less than 5% of the ions segregate into the crystals. In contrast to that, up to 50% of the Pr3+ ions are found in the crystals. It is shown that virtually complete segregation of the Pr3+ ions into the crystals is necessary for efficient amplifier operation. Glasses in the yttria-alumina-silica system are prepared and characterized with a view both as a host material for rare earth and transition metal ions, and as a precursor glass for transparent glass-ceramics with YAG nanocrystals. Subsolidus crystallisation studies identify a glass composition promising for YAG glass-ceramics, but also highlight the problem of surface crystallisation. Thulium doped YAS glass is identified as a potential gain medium for a S-band amplifier, because the fluorescence band at 1.47µm has a width of 125nm with an estimated quantum efficiency of 20%. Spectroscopy on Er3+-doped YAS glass shows that the glass can accommodate 26000ppm Er3+ without clustering. The prospect of a Cr4+:YAG glass-ceramic fibre amplifier is discussed
Distopias anacrônicas: tensões construtivas entre imagem digital e artesanal
No full textOs processos de construção de imagens que tomam o cruzamento como estratégia artística abarcam grande parte da produção atual em artes visuais. Neste artigo são abordadas as produções recentes de Flavya Mutran e Jander Rama, cujas práticas transitam entre o anacronismo dos processos de produção de imagens manuais frente à visão distópica em relação aos avanços das imagens numerizadas. O trânsito destas produções entre a gravura, o desenho ou a fotografia levantam questões sobre as tensões e deslocamentos do sujeito na arte contemporânea, provocadas pelo embate entre novas e velhas tecnologias
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
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
Processos artísticos do pós-humano em Fritz Kahn e Jander Rama
No full textA figura do pós-humano aparece intensamente nas produções de ficção científica em diversas mídias. Aqui, se pretende analisar como esse processo atinge as artes visuais, focando em trabalhos de Fritz Kahn e Jander Rama. A inovação técnica trouxe recursos estéticos diferenciados para a produção artística. Assim, a reflexão sobre a tecnicidade da cultura permeia as artes visuais no próprio fazer artístico, lançando também as propostas estéticas que configuram a visualidade desse corpo pós-humano
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
A Survey on the Use of the Multi-agent Paradigm in Coordination of Connected and Autonomous Vehicles
No full textIn this paper we present our work of searching, filtering and selecting relevant papers about the exploitation of the multi-agent paradigm in self-driving vehicles, along with the results of our survey
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
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