1,720,989 research outputs found
Advanced solid-state lasers 2019: Focus issue introduction
No full textThis joint issue of Optics Express and Optical Materials Express features 17 state-of the art articles written by authors who participated in the international conference Advanced Solid-State Lasers held in Vienna, Austria, from September 29 to October 3, 2019. This introduction provides a summary of these articles that cover numerous areas of solid-state lasers from materials research to sources and from design to experimental demonstration
Generation of 15-nJ pulses from a highly efficient, low-cost multipass-cavity Cr[superscript 3+]:LiCAF laser
No full textWe describe the generation of enhanced pulse energies using a multipass-cavity (MPC) Cr[superscript3] +:LiCAF laser, pumped by inexpensive, single spatial mode laser diodes. A semiconductor saturable absorber was used for stable mode-locked operation. The MPC reduced the pulse repetition rate to the ~10 MHz level, scaling pulse energies and intensities. With only 540 mW of absorbed pump power, 98 fs pulses with energies of 9.9 nJ and peak powers of ~101 kW, corresponding to 95 mW of average power at a repetition rate of 9.58 MHz, were generated. By increasing the intracavity negative dispersion, 310 fs pulses with energies of 15.2 nJ and peak powers of ~49 kW, corresponding to 160 mW of average power at 10.51 MHz repletion rate, were also generated. These results demonstrate that low-cost MPC Cr[superscript 3+]-doped colquiriite lasers can generate pulse energies and intensities comparable to more expensive Ti:sapphire lasers
Comparative Spectroscopic Investigation of Tm3+:Tellurite Glasses for 2-μm Lasing Applications
No full textWe performed a comparative spectroscopic analysis on three novel Tm3+:tellurite-based glasses with the following compositions Tm2O3:TeO2-ZnO (TeZnTm), Tm2O3:TeO2-Nb2O5 (TeNbTm), and Tm3+:TeO2-K2O-Nb2O5 (TeNbKTm), primarily for 2-μm laser applications. Tellurite glasses were prepared at different doping concentrations in order to investigate the effect of Tm3+ ion concentration as well as host composition on the stimulated emission cross sections and the luminescence quantum efficiencies. By performing Judd–Ofelt analysis, we determined the average radiative lifetimes of the 3H4 level to be 2.55 ± 0.07 ms, 2.76 ± 0.03 ms and 2.57 ± 0.20 ms for the TeZnTm, TeNbTm and TeNbKTm samples, respectively. We clearly observed the effect of the cross-relaxation, which becomes significant at higher Tm2O3 concentrations, leading to the quenching of 1460-nm emission and enhancement of 1860-nm emission. Furthermore, with increasing Tm2O3 concentrations, we observed a decrease in the fluorescence lifetimes as a result of the onset of non-radiative decay. For the 3H4 level, the highest obtained quantum efficiency was 32% for the samples with the lowest Tm2O3 ion concentration. For the 1860-nm emission band, the average emission cross section was determined to measure around 6.33 ± 0.34 × 10−21 cm2, revealing the potential of thulium-doped tellurite gain media for 2-μm laser applications in bulk and fiber configurations
Compact and efficient femtosecond lasers
No full textThe development of femtosecond (fs) lasers has continued rapidly since the demonstration of fs Ti:Sapphire systems in 1989. Recent research has yielded lasers which offer greatly enhanced performance in all areas. In this document we describe the development of femtosecond lasers with electrical to optical efficiency > 14%, pulse repetition frequencies > 4GHz and compact and stable cavities. We further outline the use of such lasers for the generation of high power visible femtosecond pulses and their application within systems environments for ultrahigh speed data communications, ultrafast optical switching and optical analogue to digital conversion. We also describe progress in the development of femtosecond lasers based on both active and passive semiconductor quantum dot components.</p
Enhanced gain bandwidth of Tm3+ and Er3+ doped tellurite glasses for broadband optical amplifier
No full textIn this work, (90-x-y)TeO2-10GeO(2)-(x)Tm2O3-(y)Er2O3 composition of germano-tellurite glasses were synthesized by traditional melting and quenching technique and the spectroscopic properties of synthesized glasses were investigated. The values of Judd-Ofelt (JO) intensity parameters (Omega(t)(t = 2, 4,6)), spontaneous transition probabilities (A), branching ratios (beta) and radiative lifetimes (tau(R)) were obtained by using the Judd-Ofelt (JO) theory and absorption spectra. The stimulated emission cross-sections of TG:Tm and TG:Er glasses in 1.47 mu m and 1.53 mu m wavelength regions were calculated by Fiichtbauer-Ladenburg formula and McCumber theory, respectively. The gain bandwidth-cross section product of TGTm0.5 and TGEr1 glasses was found to be 445.76 x 10(-28) cm(3) and 849 x 10(-28) cm(3), respectively. The fluorescence lifetime measurements were done for the F-3(4) and I-4(13/2) levels to compare with the radiative lifetimes. These results suggest that the TG:Tm and TG:Er studied glasses can potentially possess wider gain bandwidth for S-band amplifier and broadband optical amplifier WDM at 1.53 mu m, respectively
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
Generation of sub-150-fs, 100 nJ pulses from a low-cost cavity-dumped Cr:LiSAF laser
No full textWe report a low-cost, cavity dumped Cr:LiSAF laser, generating 135-fs pulses at 825 nm, with 105 nJ pulse energies and ∼0.78 MW of peak power at 10 kHz, using only 600 mW of pump power
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
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