1,720,959 research outputs found
Power scaling of high power lasersystems
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The Non Uniform Adaptive Angular Spectrum Method and its Application to Neural Network Assisted Coherent Beam Combining
Full text linkIncreasing the number of laser beams that can be coherently combined requires accurate and fast algorithms for compensating phase and alignment errors. The paper proposes to use a Fully Connected Artificial Neural Network (FCANN) to correct the beam positioning perturbations by evaluating the beam shifts and tilts from two images taken at slightly different locations. Then, since it is practically impossible to have a large enough experimental dataset to train the neural network, this approach required developing an accurate and fast simulation method to evaluate the beam propagation in arbitrary directions, overcoming the limitations occurring when the computation must be repeated a large number of times. The numerical approach is a variant of the Angular Spectrum (AS) method, called Non Uniform ADaptive Angular Spectrum (NUADAS) method, which relies on the combination of non-uniform and adaptive Fourier transform algorithms to allow the computation of an arbitrary field distribution in a plane that is shifted and tilted with respect to the source. The parallel implementation of the NUADAS method is discussed and the numerical and experimental validations are presented. Then, an FCANN is trained using the synthetic dataset generated with the NUADAS method and the results are discussed, demonstrating the viability of the proposed approach not only for coherent beam combing, but also in other beam alignment applications
Power scaling of laser diode modules using high-power DBR chips
Full text linkA family of laser diode modules emitting hundreds of watt and based on intrinsically wavelength stabilized narrow linewidth high-power Distributed Bragg Reflector (DBR) chips has been manufactured and fully characterized. The module layout exploits a proprietary architecture to combine through spatial and wavelength multiplexing several highly manufacturable chips that integrate a grating and therefore do not require additional external stabilization devices to allow dense wavelength multiplexing. Power levels going from 200W to 400W in a 135 micron core fiber have been achieved using two to four wavelengths. The narrow spectral emission of each chip makes the modules suitable not only for direct-diode material processing, but also for laser pumping
Compact high-brightness and highly manufacturable blue laser modules
Full text linkBlue laser diode sources have already proved to be an effective alternative for material processing, especially of high reflective materials, such as copper; now the challenge is to increase their power while improving brightness and reducing the cost-per-watt. The paper presents the development of a family of blue laser modules that, making use of the same platform and assembly lines of similar 9xx nm modules, can achieve an unprecedented combination of power, brightness, compactness and cost reduction. These modules rely on a proprietary architecture to combine a plurality of chips through spatial and polarization multiplexing, obtaining up to 100W of output power in a 100 μm fiber. Preliminary experimental results for module making use of spatial multiplexing report 35W output power in a 50 μm fiber
Preliminary investigation of radiation dose sensors based on aluminum-doped silicate optical fibers
Full text linkThe paper reports on the first demonstration of in-situ, real-time dosimetry realized with an enhanced back-scattering optical fiber and a high-resolution optical back-scattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular the difficult evaluation of not only the actual x-ray dose that is accumulated on the target volume, but also the distribution profile of the ionizing radiation beam. The experiments have been conducted by evaluating the radiation-induced spectral shift of the Rayleigh back-scattering along the fiber under test during x-ray exposure, in a radiation chamber. The sensing region is a section of aluminum-doped silicate fiber, that overcomes the poor sensitivity to radiation of standard, germanium-doped, silicate fibers for telecom applications. The preliminary results show that it is possible to remotely track the x-ray dose at high dose rates (700 Gy/min) and at rates closer to therapeutic values (22 Gy/min). A linear relationship between accumulated dose and spectral shift has been found. This research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling and remote interrogation
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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