1,720,958 research outputs found
Laser performance and spectroscopic analysis of optically written channel waveguides in neodymium-doped gallium lanthanum sulphide glass
Full text linkWe present a spectroscopic analysis and laser characterization of optically written waveguides in neodymium-doped gallium lanthanum sulphide (Nd3+-Ga:La:S) chalcogenide glass. Uniform channel waveguides were fabricated in Nd3+-Ga:La:S by exposure to radiation from a focused uv-laser beam (λ = 244nm), producing a refractive index change Δ.n ~ +10-3. The observed laser performance and fluorescence decay were in good agreement with values calculated from a spectroscopic analysis of 85µs for the 4F3/2 lifetime and 5.9 x 10-20cm2 for the emission cross-section at 1075nm. Low threshold laser operation with emission at 1075nm and a slope efficiency of 17% is demonstrated. The active device is spatially single-mode and exhibits up to 8.6mW output power and propagation losses of <0.5 dB cm-1. Waveguide fabrication, photoinduced effects and optical characterization in terms of spectroscopy, laser performance and device attenuation are discussed
Gain measurements at 2.8µm and fluorescence spectroscopy in Er:LaF<sub>3</sub> waveguides fabricated by molecular beam epitaxy
No full textThe potential of MBE rare-earth-doped LaF3 thin films in the IR region has been previously reported by our group. Despite an unfavourable electron-phonon coupling which does not permit access to efficient transitions far above 3µm, LaF3 still offers the advantage of a very low phonon energy (~380 cm-1) and high transparency in the 2µm - 3µm range. Therefore it appears very attractive to fabricate a 2.8µm laser device based on this technology, with erbium as the doping ion, as the waveguide geometry should lead to a low-threshold, efficient, integrated device that operates continuously at room-temperature.Several erbium-doped LaF3 thin films were grown on (111) oriented CaF2 substrates with core depths in the 2µm range, both with or without CaF2 claddings. The design with a cladding gives a high NA of 0.7 and offers single mode properties and good vertical confinement at 2.8µm as shown in figure 1. Three samples of 19 mm length, with respective concentrations of 1.08, 5.1 and 8.9 at. %, were grown by this method for investigation
Development of channel waveguide lasers in Nd<sup>3+</sup>-doped chalcogenide (Ga:La:S) glass through photoinduced material modification
No full textWe report the development of a waveguide laser source in a neodymium-doped chalcogenide (Ga:La:S) glass. Channel waveguide structures were directly written via above band gap (λ=244 nm) illumination provided by a focused UV-laser beam with fluencies 1.5–150 J/cm2. Effects of photoinduced material modification in the form of surface compaction and photodensification were evident. Characterization revealed a low threshold waveguide laser with emission at 1075 nm and slope efficiency of 17%. The active device was spatially single mode and exhibited laser operation with 8.6 mW peak power and attenuation <0.5 dB cm–1
Low phonon energy Nd:LaF<sub>3</sub> channel waveguide lasers fabricated by molecular beam epitaxy
No full textWe report the first fabrication and laser operation of channel waveguides based on LaF3 planar thin films grown by molecular beam epitaxy. To our knowledge, this is the lowest phonon energy dielectric material to have shown guided-wave laser operation to date. A full characterization, in terms of spectroscopy, laser results, and propagation losses, is given for the planar thin films upon which the channel waveguides are based. Two channel-fabrication methods are then described, the first involves ion milling and the second takes the novel approach of using a photo-definable polymer overlay. Laser operation in Nd-doped samples is demonstrated at 1.06, 1.05, and 1.3 µm, and the potential for mid-infrared laser sources based on such guides is discussed
Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser
Full text linkHighly-efficient repetitive passive Q-switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by employing an external cavity configuration containing a Co2+:ZnS crystal as saturable absorber. Energies up to 60µJ in pulses of duration as short as 3.5ns (FWHM), corresponding to a peak power >10kW, have been generated, and the maximum slope efficiency with respect to absorbed pump power was 13%. Using a bulk diffraction grating in Littrow configuration to provide wavelength selective feedback, the passively Q-switched fiber laser was tuned over 31nm from 1532nm to 1563nm. The prospects for further improvement in performance will be discussed
Diode-pumped passively Q-switched tunable Er-Yb double-clad fibre laser
No full textReliable passive Q-switching of a cladding-pumped Er-Yb fibre laser at 1532-1563nm has been demonstrated using cobalt-doped ZnS crystal as saturable absorber. High peak powers >10kW were obtained for ~2.75W of absorbed pump power at 915nm
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
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