1,720,957 research outputs found
High power single-frequency continuous-wave Nd:YVO<sub>4</sub> master-oscillator power amplifier
No full textWe report a highly-efficient, high-power, single-frequency Nd:YVO4 master-oscillator power-amplifier with near-diffraction-limited output beam quality. A diode-pumped Nd:YVO4
ring laser incorporating a passive method for suppressing
axial-mode-hopping was employed as the master-oscillator, and was
amplified by a three-stage diode-end-pumped Nd:YVO4
amplifier, yielding 79 W of output with an extraction efficiency of 29%.
The overall power gain was 15 dB for an input power from the
master-oscillator of 2.4 W, and the M2 parameter was less
than 1.5 at the maximum power. The prospects for a further increase of
power and brightness via this approach are considered
Influence of gain-guiding on beam quality in a thermally aberrated end-pumped Nd:YVO<sub>4 </sub>amplifier
No full textBeam quality degradation caused by aberrated thermal lensing in an end-pumped Nd:YVO4 amplifier is found to be offset by the effect of gain-guiding. Significantly improved beam quality is observed in unsaturated, high gain conditions
High power, long pulse duration, single-frequency Nd:YVO<sub>4</sub> master-oscillator power-amplifier
No full textAn efficient single-frequency Nd:YVO4 master-oscillator power-amplifier is described. Gated pulses from a CW diode-pumped ring laser were amplified by three Nd:YVO4 amplifiers. Pulses of 1mJ energy; 2kW peak power and 1µs duration were obtained at a repetition frequency of 10kHz. Analogue shaping of the input pulses was used to control the output pulse shape and thus extend the useful range of pulse widths from the ~100ns to the ~µs regime. A simple mathematical expression was used to model the results which provided reasonable agreement with the experimental work. This system offers a promising pump source for a quasi-CW singly-resonant optical parametric oscillators
High average power end-pumped Nd:YVO<sub>4</sub> master oscillator power amplifier
No full textWe demonstrate 94 W average power from an all-solid-state fibre-coupled diode end-pumped Nd:YVO4 master oscillator and multi-stage power amplifier
Simple technique for measuring the energy-transfer-upconversion parameter in solid-state laser materials
Get PDFScaling the output power from solid-state lasers to higher power levels, whilst maintaining high efficiency and good beam quality is a challenging task. The chief difficulty is heat generation and its deleterious effects on laser performance. The main origin of heat generation is often considered to be quantum defect heating. However, many solid-state laser media also suffer from the problem of energy-transfer-upconversion, which can lead to a dramatic reduction in the effective upper laser level lifetime and a large increase in the fractional heat loading unless appropriate measures are taken. Thus, an accurate knowledge of the upconversion parameter and the impact of upconversion on laser performance is very important for power scaling of solid-state lasers, particularly when operating in pulsed (Q-switched) mode. The standard method for determining upconversion parameters, based on measurements of fluorescence decay times, can be quite time consuming and requires very careful attention to detail in the experimental set-up and pumping conditions if it is to yield accurate values
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
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