1,721,041 research outputs found
Diode-side-pumped channel waveguide laser
No full textFundamental-mode channel waveguide lasers, while offering high pump and signal intensities and excellent pump-signal mode overlap, usually require a fundamental-mode pump source, thus limiting the diode pump power that can be launched into the waveguide to typically less than 1 W, thereby also setting limitations on the achievable output power. Here we demonstrate laser emission from a highly Yb3+-doped, tapered channel waveguide in KGdxLu1-x(WO4)2 by diode side pumping with a high-power, multi-mode diode bar via a passive planar waveguide, offering the potential for significantly increased output powers. We have chosen KGdxLu1-x(WO4)2:Yb3+ for its large pump-absorption cross-section at 981 nm. Multi-layer growth of lattice-matched layers [1] with various compositions is applied to design the refractive-index contrast and active properties of the laser device (Fig. 1). A 1.7 to 0.6-µm-high, horizontally tapered waveguide structure is etched into the 5mm-long KGd0.447Lu0.078Yb0.475(WO4)2 active layer [2] to allow for efficient pump absorption under side pumping in its 50-µm-wide waveguide section and simultaneously ensure single-mode laser emission via its 5-µm-narrow waveguide section. The pump power is delivered from the side through a 5 to 2.5-µm-high passive KGd0.114Lu0.116Y0.77(WO4)2 slab waveguide overgrown and surrounding the active tapered waveguide. The multi-mode, 30-W diode bar is mounted on a water-cooled chuck without active temperature control, resulting in a pump wavelength around 980 nm (Fig. 2a). The pump beam is modulated by a chopper with 2.9% duty cycle to reduce the thermal load. Mirrors are butt-coupled to the waveguide endfacets by use of a fluorinated oil, with reflection at 1040 nm of 99.8% and 90% at the wide and narrow active-waveguide end, respectively. No additional measures are taken to cool the sample. With this first, non-optimized device a maximum output power of 10 mW (Fig. 2a) when pumped with a cold diode (operating close to the absorption peak) and laser wavelength of 1038nm (Fig. 2b) are detected. Relaxation oscillations and the mode profile of laser emission with satellite spots, indicating a non-ideal taper structure, are recorded (Fig. 2c)
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
99-fs Nd:glass laser mode-locked with carbon nanotube saturable absorber mirror
No full textMode-locked operation of Nd:silicate glass with both single-walled carbon nanotubes (SWCNT-SAM) and semiconductor saturable absorber mirrors (SESAM) has been investigated. SWCNT-SAM mode-locking has been optimized in Nd-doped bulk lasers for the first time, yielding 99-fs pulses at 1070 nm. Using a SESAM for comparison pulses as short as 87 fs and a tuning range of 30 nm was achieved. Related to the applied 200-mW single-mode laser diode as pump source the lasers were characterized by high efficiency and low threshold. The optimized low-power pump setup yielded a remarkable slope efficiency of 46.5% in the cw regime
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
Generation of 40ns laser pulses by a diode-pumped passively Q-switched Tm-Ho:YLF laser
No full textWe demonstrate for the first time generation of short pulses from a repetitively passively Q-switched Ho-laser that is diode-pumped near 800 nm by codoping with Tm-ions. The laser material used is the well-known fluoride crystal Tm,Ho:LiYF4 and polycrystalline Cr:ZnSe was employed as a saturable absorber. The maximum peak power achieved was ~640 W and the emission wavelength was ~2050 nm
Energy scaling of a carbon nanotube saturable absorber mode-locked femtosecond bulk laser
No full textWe report successful energy scaling of a room-temperature femtosecond Cr4+: forsterite laser by using a single-walled carbon nanotube saturable absorber (SWCNT-SA). By incorporating a q-preserving multipass cavity, a repetition rate of 4.51 MHz was realized, and the oscillator produced 121 fs, 10 nJ pulses at 1247 nm, with an average output power of 46 mW. To the best of our knowledge, the peak power of 84 kW is the highest generated to date from a SWCNT-SA mode-locked oscillator. Furthermore, energy scaling of a femtosecond multipass-cavity laser, mode-locked using a SWCNT-SA, is demonstrated for the first time. (c) 2012 Optical Society of Ameri
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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