1,721,074 research outputs found
Power Scaling of Mid-Infrared and Two-Micron Laser Sources
No full textOne of the most efficient methods for generating laser light in the 3–5 µm mid-infrared wavelength band involves the use of an optical parametric oscillator (OPO) to convert an incident pump photon into two longer-wavelength photons. By using a pump laser at a wavelength around 2 µm, both of the output photons from the OPO can be in the 3–5 µm band, greatly improving the conversion efficiency. Due to the nonlinear nature of the conversion process, a high-peak-power pump laser is essential for overcoming the large OPO threshold intensity, with pulsed lasers and amplifiers based on Ho:YAG being particularly attractive for such operation due to a natural emission peak at 2090 nm (where the absorption losses of OPO crystals are generally much lower than for shorter wavelengths) and a large energy storage capability. Ho:YAG sources are often pumped by continuous-wave thulium-doped fibre lasers in order to target the 1907 nm absorption line of the Ho:YAG crystals. However, all three stages (thulium fibre, Ho:YAG and OPO) suffer from a variety of intrinsic challenges that limit their operation at high average power levels, which have been investigated here.A novel dopant distribution profile has been explored within the core region of a cladding-pumped thulium fibre laser in order to permit much longer device lengths to be utilised and greatly improve the thermal management at high power levels, without being hampered by the onset of long-wavelength parasitic lasing before 1907 nm emission can be achieved. Up to 131 W of continuous-wave 1907 nm output is demonstrated from a single 6-metre-long section of nested-ring thulium-doped fibre, with the potential for adapting the nested-ring design to target other wavelengths that are limited by parasitic lasing also being examined. A high power master-oscillator power-amplifier Ho:YAG source has been developed using a 23.7 W, 36 ns Q-switched Ho:YAG seed laser which is injected into a two-stage amplifier system. Two 160 W all-fibre 1907 nm thulium pump sources were developed to single-end-pump the two amplifier crystals and greatly reduce the system complexity in comparison to alternative 1907 nm pump sources, generating up to 85 W of 2.1 µm output. The power scaling of radially polarised light at 2.1 µm has also been explored using Ho:YAG sources, including a 33.7 W double-pass thin-slab amplifier where the onset of depolarisation has been particularly targeted for mitigation. A 20.6 W radially polarised laser has also been demonstrated which uses an intra-cavity laser-written S-waveplate device to allow the simultaneous generation of radial polarisation and cavity Q-switching with up to 0.5 mJ pulse energy and a 210 ns pulse duration. Lastly, the potential advantages of using a highly-elliptical pump beam in a mid-infrared OPO are explored, initially by pumping the OPO directly with the 23.7 W Q-switched Ho:YAG seed laser, generating up to 3.7 W of mid-infrared output power for a 13:1 aspect ratio pump spot. The opportunity for further OPO power scaling when pumped with the 85 W MOPA output is also considered
Dataset to support the paper '33 W radially polarized emission from a double-pass Ho:YAG thin-slab amplifier'
No full textDataset for '33 W radially polarized emission from a double-pass Ho:YAG thin-slab amplifier' in Journal of the Optical Society of America B.
This dataset contains the data used in the generation of Figures 2 and 4 in the manuscript.
The figures are as follows:
Fig. 2. Output power curve for the radially polarized Ho:YAG seed laser. Inset, top-left: emission spectrum at 13.2 W. Inset, bottom-right: near-field ring-shaped pump beam profile.
Fig. 4. Output power curve for the Ho:YAG thin-slab amplifier with a 13.2 W seed input. Inset, top-left: simulated variation in pump and seed beam areas along the length of the crystal. Inset, bottom-right: amplifier gain versus absorbed pump.</span
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Nested-ring doping for highly efficient 1907 nm short-wavelength cladding-pumped thulium fiber lasers
No full textCladding-pumped Tm-doped fiber lasers operating below 1950 nm have difficulty matching the high-efficiency, power-scalable output that can be achieved at longer wavelengths. This challenge arises due to the strong three-level behavior at short wavelengths and strong competition from higher-gain long wavelength emission. In this Letter, we demonstrate a nested-ring fiber design in which a highly doped Tm ring is embedded within a larger undoped core. The fiber is specifically tailored for highly efficient and high power short-wavelength operation (<1950 nm). The nested-ring Tm fiber laser has generated 62 W of single-mode 1907 nm output with up to 65% (70%) slope efficiency with respect to launched (absorbed)pumppower.</p
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