1,720,961 research outputs found
Spectral gain and cavity loss characterization of an optically-pumped external-cavity surface-emitting quantum well laser
No full textWe present the spectral gain and cavity loss characterisation of an optically-pumped external-cavity 1-µm surface-emitting InGaAs quantum well laser by observing the evolution of intracavity power and spontaneous emission following the uncovering of the cavity mode by an intra-cavity chopper. The smooth monotonic rise (fall) is characteristic of an external-cavity quantum well laser where the photon lifetime is approximately two orders of magnitude higher than the carrier lifetime
Wetting-layer-pumped continuous wave surface emitting quantum dot laser
No full textWe report a continuous wave 1 µm laser based on InAs Stranski-Krastanov quantum dots (SK-QD) which is optically pumped on a wetting layer absorption band at 915 nm. The slope efficiency of this laser relative to absorbed pump power was measured to be 56% with wetting layer pumping, 1.75 times larger than when pumped with 830 nm light absorbed into the barriers between the SK-QD layers. Compared to barrier pumping, wetting layer pumping benefits from a smaller quantum defect, with less heat deposited in the active region, at the expense of weaker pump absorption in the thin (~1 nm) wetting layer. When a 50 µm thick intracavity diamond heatspreader was contacted to the optically pumped gain structure, a 10-fold increase in output power, up to 2.25W, was obtained in the barrier pumped case. A much smaller 2-fold increase in power, to a maximum of 0.35 W, was seen for the wetting layer pumped case. The diamond heatspreader is more effective in removing heat from the active region, where it is deposited by barrier pumping, than from the substrate, which absorbs residual pump radiation in the barrier pumping case. A gain sample with a doubly periodic DBR to back reflect pump radiation, will allow the full potential of wetting layer pumping to be realised, both by increasing pump absorption due to the double pass through the active region, and by localising heat generation in the active region
Wetting-layer-pumped continuous-wave surface-emitting quantum-dot laser
No full textQuantum-dot vertical-external-cavity surface-emitting lasers (QD VECSELs) are of interest due to their large inhomogeneous gain spectrum and the potential for temperature insensitivity and low threshold. We report a QD VECSEL which is wetting-layer-pumped using a 915-nm diode laser, reducing the quantum defect compared to barrier pumping. A slope efficiency of 56% relative to absorbed pump power was measured from an unprocessed sample with a heat-sink temperature of -30 °C, 1.75× higher than when barrier pumped using an 830-nm pump diode
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
Photon-pair generation in photonic crystal fibre with a 1.5 GHz modelocked VECSEL
Full text linkFour-wave mixing (FWM) in optical fibre is a leading technique for generating high-quality photon pairs. We report the generation of photon pairs by spontaneous FWM in photonic crystal fibre pumped by a 1.5 GHz repetition-rate vertical-external-cavity surface-emitting laser (VECSEL). The photon pairs exhibit high countrates and a coincidence-to-accidental ratio of over 80. The VECSEL's high repetition-rate, high average power, tunability, and small footprint make this an attractive source for quantum key distribution and photonic quantum-state engineering
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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