1,720,962 research outputs found
Wavelength-flexible thulium-doped fiber laser employing a digital micro-mirror device tuning element
No full textWe demonstrate a cladding-pumped thulium-doped fiber laser using a digital micromirror device based wavelength selection element. Tunability over 121nm was achieved with up to 8.4W of output power as well as multi-wavelength operatio
Phase-conjugate self-organized coherent beam combination
No full textRecently, the improvement of diode pumping in solid state lasers and the development of double clad fiber lasers have allowed to maintain excellent laser beam quality with single mode fibers. However, the fiber output power if often limited below a power damage threshold. Coherent laser beam combining (CLBC) brings a solution to these limitations by identifying the most efficient architectures and allowing for excellent spectral and spatial quality. This knowledge will become critical for the design of the next generation high-power lasers and is of major interest to many industrial, environmental, defence and scientific applications. The purpose of this book is to present the more recent concepts of coherent beam combining by the world leaders in the field. After a general presentation of laser beam combining and associated challenges, the book will review functionalities and techniques in details with an emphasis on practical implementations. Thus both scientific and engineering aspects are addressed
Monolithic 272W high efficiency Tm-doped nested-ring fibre laser
No full textThulium fibre lasers represent an important system in applications such as medical treatments, materials processing, remote sensing, non-linear frequency conversion, LIDAR, and defence applications [1]. High-power thulium lasers are mainly based on 790 nm cladding pumping schemes, which allow exploitation of a two-for-one cross-relaxation process with theoretical efficiency up to 80 %. However, power scaling beyond 150 W, in general, requires utilisation of LMA fibres, which suffer from lower efficiencies [2]. The nested-ring fibre was proposed to investigate the power-scaling potential of a novel non-uniform Tm doping profile employed across a small core diameter without pedestal. The confinement of Tm
3+ doping to a thin ring towards the outer edge of the fibre core reduces the spatial overlap between the propagating mode and the doped region. This allows efficient operation at the shorter wavelengths without the onset of parasitic lasing at longer wavelengths. Crucially, this design also reduces pump absorption per unit length, while still maintaining a high Tm
3+ doping concentration within the doped region of the core (4 wt. %), to allow efficient exploitation of the two-for-one cross-relaxation process. This reduces the thermal load density of the fibre, allowing for a greater power extraction before thermally-induced failure [3].</p
Nested-ring Tm-doped high-power widely tunable fiber laser
No full textA structured thulium-doped nested-ring active fiber was used to build a widely tunable high-power fiber laser. The nested-ring fiber allows high-power cladding pumping along with enhanced thermal management, improvement in the efficiency of the two-for-one process, and enabling single-mode operation. The straightforward tunable cavity design permits remote tuning while ensuring full enclosure of free-space optics and purification with nitrogen to mitigate the effects of water vapor absorption on the lasing process. Our study introduces a tunable Tm-fiber laser capable of emitting in the 1930 to 2090 nm range with a linewidth of 0.2 nm, delivering stable output power up to 70W.</p
Monolithic highly-efficient 272 W nested-ring structured-core thulium fibre laser at 1940 nm
No full textA novel, to the best of our knowledge, thulium-doped silica fiber with a non-uniform core doping profile has been utilized to demonstrate a high-power monolithic laser oscillator system. The fiber laser achieved a continuous-wave (CW) output power of 272W at 1940nm with slope efficiencies of 68% and 71% with respect to launched and absorbed pump power, respectively. This novel Tm fiber design enabled the generation of the highest reported output power from a single-mode, small core (<15µm diameter) non-pedestal fiber. Moreover, the slope efficiency achieved is the maximum reported to date for a single-mode thulium fiber laser operating at >100 W output power level.</p
High power fiber lasers with radially polarized output beams
No full textA scheme for directly exciting the radially-polarized TM01 mode in a fiber laser is reported. Preliminary results for cladding-pumped ytterbium-doped and thulium-doped fiber lasers are discussed along with prospects for scaling to high power levels
Ring-doped Tm fibres for high-efficiency cladding-pumped 1907 nm lasers
No full textA cladding-pumped Tm fibre is designed and fabricated with a ring-structured fibre core geometry, optimised for power-scalable, single-mode 1907 nm operation with 67.0% slope efficiency and demonstrated in an all-fibre laser oscillator configuration
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
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