1,720,977 research outputs found
Efficient second-harmonic generation through cascaded optically poled fibers
No full textWe report the experimental demonstration of efficient second-harmonic generation by splicing optically poled fiber segments. A device made from five segments each 20 cm-long exhibits, at a fundamental average power of 4.2 mW, a maximum increase of 5.5 in the conversion efficiency with respect to a single 20 cm poled fiber, corresponding to a conversion efficiency of 5.4%. For any considered fundamental power, the conversion efficiency at the output of a five-segment device is larger than the efficiency of a single poled fiber having the same length
Spatial beam self-cleaning dynamics in Erbium-Ytterbium (Er-Yb) codoped multimode fiber
No full textWe demonstrate self-induced high beam quality recovery in Er-Yb codoped multimode active fiber with parabolic refractive index profile of the core. Nonlinear beam cleanup is accompanied by Raman and parametric instability sideband generation
Glass Fiber Poling by an Extended Cavity Microchip Laser
Get PDFWe experimentally prove that glass fibers are efficiently optically poled when inserted in the extended cavity of a microchip laser. Methodical second harmonic measurements confirm the good quality of the poling
Survey of second harmonic generation in commercial germanium-doped fibers
No full textSeeded optical poling is a promising and simple method to write an effective quadratic coefficient in silica optical fibers doped with germanium. We considered commercial solid core fibers since these fibers could allow for a wide adoption of optical poling. For each fiber, we optimized the poling process and analyzed the second harmonic conversion efficiencies in relation with the fiber chemical composition as obtained resorting to energy -dispersive X-ray spectroscopy. Our comprehensive investigation shows that segments of fibers spanning 20 cm, featuring a germanium content of around 6%, can effectively convert 30 mW of 1064 nm light with efficiencies hovering around 1%. (c) 2023 Optica Publishing Grou
Second Harmonic Generation in Spliced Poled Fibers
No full textOptical poling is a very simple technique for inducing a quadratic nonlinearity in germanium-doped silica fibers [1], [2]. By injecting into the fiber fundamental frequency (FF) pulses together with a low power second harmonic (SH) seed, a multi-photon quantum interference process naturally generates a quadratic nonlinearity whose period satisfies the quasi-phase matching (QPM) condition. The nonlinear grating writing process takes a few hours before showing a saturation of the SH conversion efficiency, which is always lower than the best values achievable by resorting to thermal poling [3]. Also, the maximum length of the poled region exhibits saturation, and this hampers the SH generation [4]
Direct Gaussian to high-order Laguerre-Gauss beam shaping in GRIN multimode fiber
No full textWe report our observation of direct transformation of a Gaussian-like laser beam, initially injected into the cladding of a graded-index multimode fiber, into a high-order Laguerre-Gauss mode within the fiber core
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
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