1,720,959 research outputs found
High gain Nd:YLF amplifier end-pumped by a beam-shaped broad-stripe diode laser
No full textThe output from a 1W broad-stripe diode, reshaped by a two-mirror beam-shaper, is used to end-pump a Nd:YLF amplifier. In a double-pass configuration a small-signal gain of 240 has been obtained
High-power quasi-cw laser pulses via high-gain diode-pumped bulk amplifiers
No full textBy pulse-slicing from a cw laser output and then providing high gain amplification, one can obtain quasi-cw pulses at powers well in excess of those available from cw lasers. The use of this is demonstrated with a cw, additive-pulse-mode-locked Nd:YLF laser. Mode-locked pulse trains with an envelope of ~10µsec duration and repetition rate of 2kHz are amplified in a x20 gain, double-pass Nd:YLF bulk amplifier pumped by a 4W diode. Amplified power levels allow efficient single-pass frequency doubling in LBO followed by efficient synchronous pumping of an LBO optical parametric oscillator
Energy-transfer upconversion and thermal lensing in high-power end-pumped Nd:YLF laser crystals
Full text linkThermal lensing in an end-pumped Nd:YLF rod, under lasing and non-lasing conditions, has been investigated. Under lasing conditions a weak thermal lens, with dioptric power varying linearly with pump power, was observed. Under non-lasing conditions where higher inversion densities are involved, hence relevant to Q-switched operation or operation as an amplifier, a much stronger thermal lens was measured, whose power increased non-linearly with pump power. This difference has been attributed to the increased heat deposition due to the subsequent multiphonon decay following various interionic upconversion processes, which increase strongly under non-lasing conditions, and is further exacerbated by the unfavourable temperature dependencies of heat conductivity and rate of change of refractive index with temperature. A strategy for reducing upconversion and its associated thermal loading, without degrading laser performance, is discussed
Synchronous pumping of an optical parametric oscillator using an amplified quasi-cw pump envelope
No full textPulse-slicing from a cw laser output followed by high gain amplification can produce quasi-cw pulses at power levels well in excess of those available from large frame cw lasers. Mode-locked pulse trains with an envelope of 10µs duration and at 2kHz repetition rate are amplified by a factor of 20 to give 5 Watts of envelope average power. These power levels allow efficient single-pass frequency doubling and subsequent pumping of a lithium triborate optical parametric oscillator
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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