1,720,966 research outputs found
7.7mJ pulses from a large core Yb-doped cladding pumped Q-switched fibre laser
No full textWe investigate Q-switching of a cladding-pumped ytterbium-doped fibre laser with a 60µm core diameter. We reached 7.7mJ pulse energy at 500Hz repetition rate, and 10W output power at high repetition rates in a highly multi-moded beam
Pulsed fibre laser and amplifier systems
No full textTremendous progress has been made over recent years in the development of high-power fibre laser systems. Gone are the days when fibre lasers were perceived as an irrelevant curiosity offering interesting performance features but always at a power level that seemed inadequate for all but a few niche applications. Improvements in high-power, high-brightness multi-mode pump lasers, coupled with the development of cladding-pumped laser technology, have changed that view. It is now widely appreciated that the excellent heat dissipation characteristics of fibre along with the high efficiencies (often greater than 80%), actually make fibre lasers a front runner for many high power laser applications and in particular those that require the generation of high average power continuous-wave radiation. Average power levels of 110W have already been reported for a fibre laser and there is significant potential for scaling the power levels still higher. Whilst such arguments have proved compelling from the continuous wave laser perspective the suitability of fibre based systems for pulsed laser and amplifier systems is less obvious. In a conventional single-mode fibre light is confined within a mode with a characteristic diameter of order 5-10µm. This limits the energy storage of the medium and compromises laser operation for applications, such as Q-switching, which critically depend on this. Furthermore, fibres are inherently nonlinear and the tight mode confinement limits the pulse peak powers that can be reliably generated, or transmitted, through the system. Fortunately however it is possible to reduce the impact of such limitations by using advanced large mode-area single-mode fibre designs, or by going to multi-mode cores which offer even larger mode-areas. The key to successfully using the later is to manage the mode-selection and mode-coupling issues that naturally arise in order to ensure good spatial mode-quality output. Using such an approach it is possible to increase by more than two orders of magnitude the pulse energies attainable from both fibre laser, and seeded MOPA systems. For example we recently achieved ~8mJ pulses from a Q-switched fiber laser thereby opening up the possibility of using such sources for applications such as LIDAR that were previously considered incompatible with the pulse energies achievable with fibre technology. Moreover using techniques such as fibre based chirped pulse amplification it is possible to construct femtosecond pulse sources operating at several hundred pJ pulse energies and at multi-watt average power levels. Such sources are suited to a range of applications ranging from scientific research through to materials processing. In this presentation we review the latest advances in pulsed fibre laser and amplifier systems operating from the nanosecond to femtosecond regime. We discuss a number of the key application areas for such technology and conclude by making predictions for future research directions and ultimate performance limits
Jacketed air-clad cladding pumped ytterbium-doped fibre laser with wide tuning range
No full textA tunable cladding-pumped ytterbium-doped fibre laser is presented. An air-clad inner cladding supported by a micro-structured silica mesh inside a silica jacket is used. A measured inner-cladding NA of 0.4 to 0.5 enables efficient pump launch into a 36 µm-diameter inner cladding. The small inner cladding area enables tuning from 1010 to 1120 n
Widely tunable high-power diode-pumped double-clad Yb<sup>3+</sup>-doped fiber laser
No full textWe present 10W output power, 70% slope efficiency, 70nm tuning range, and/or 976nm emission from different double-clad ytterbium-doped fiber lasers end-pumped by a beam-shaped 915nm diode bar
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
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