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Rare-earth-doped gallium lanthanum sulphide glasses for mid-infrared fibre lasers
No full textGallium lanthanum sulphide (GLS) glass was investigated as a potential host material for rare-earth (RE) doped mid-infrared fibre lasers. Glasses were fabricated from gallium sulphide and lanthanum sulphide powders by melt quenching and drawn into fibres using the rod-in-tube technique. Typical values for the attenuation in the loss minimum around 4 µm are a few dB/m. The quality of the fibre is currently limited by impurities such as transitions metals, silicon, and aluminium, imperfections at the core/clad interface, and the tendency to crystallisation. Absorption, fluorescence, and lifetime measurements were performed for eleven RE ions for wavelengths ranging from the visible to the mid-infrared with a focus on mid-infrared transitions. The results of the measurements were used to study the multiphonon decay in GLS glass and to obtain important laser parameters such as the absorption and emission cross sections, branching ratios, and quantum efficiencies from the Judd-Ofelt theory, the Füchtbauer-Ladenburg equation, and the McCumber theory. Twenty-one transitions with peak emission wavelengths longer than 2 µm were identified, seven of which have not been reported in a glass before. Some transitions overlap with the fundamental absorption bands of environmentally important gases such as the 3.4 µm (methane and other hydrocarbons) and 4.7 µm (carbon monoxide) praseodymium transitions and the 4.3 µm (carbon dioxide) dysprosium transitions, whereas the 3.8 µm thulium and the 3.9 µm holmium transitions coincide with an atmospheric transmission window. Co-doping schemes such as thulium/terbium, praseodymium/ytterbium, praseodymium/erbium, and dysprosium/erbium which offer more favourable absorption bands for diode laser pumping were investigated with respect to ion-ion energy transfer. Excited-state absorption (ESA) measurements in erbium and thulium doped GLS glasses revealed transitions from excited RE energy levels to levels at energies relative to the ground state which are larger than the energy bandgap of the glass (~ 2.6 eV). Transitions from the RE ions to the conduction band of the glass, as they have been reported in RE doped crystals, could not be found. The results support the model of isolated ions with shielded 4f levels and rule out ESA from RE ions to the conduction band of the glass as a potential loss mechanism for RE lasers in GLS glass. Lasing was demonstrated in neodymium doped GLS glass and glass fibre at 1.08 µm, representing the first reported laser action in a RE doped chalcogenide bulk glass and glass fibre, respectively. The strong thermal lensing in the bulk glass rules out the use of GLS glass as a bulk laser material. The effect was eliminated by using a fibre geometry showing the advantages and necessity of GLS glass fibre
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Full text linkGamma-Ray Astronomy with MAGIC above 25 GeV
No full textThe MAGIC telescopes are 17m diameter
Cherenkov telescopes, located on the Canarian island
La Palma (Spain), with an optimal view on the
Northern sky. It is nowadays the only ground-based
instrument able to measure high-energy °-rays below
100 GeV. A recent upgrade of the trigger system
allows to extend the sensitivity down to 25 GeV, which
resulted in the detection of pulsed emission from the
Crab pulsar. The construction of the second telescope
MAGIC-II has been completed and commissioning is
in its final phase phase. We review some recent experimental
results obtained with the single telescope
MAGIC-I
Gallium lanthanum sulphide glasses for mid infrared fibre applications
No full textGallium lanthanum sulphide glasses (GLS) are a very promising material for mid-infrared optical fibre applications. The wide transmission window of ~0.6-6µm makes it suitable for passive MIR transmission for such applications as power delivery, and remote sensing. Its low phonon energy makes it a suitable host material for rare-earth doping for use in MIR active devices; the first laser action demonstrated in chalcogenide glasses and fibre was in Nd3+ doped GLS fibres. Presented is an analysis of the impurity content of GLS glasses, which currently limits the optical performance of this material, and the latest results on single mode fibres drawn from purified precursors
2.8µm emission of Er-doped CaF<sub>2</sub> planar waveguides fabricated by molecular beam epitaxy
No full textWe report the fabrication of erbium doped calcium fluoride thin film optical waveguides by molecular beam epitaxy and the luminescence study of the 2.8µm emission from a guide with an erbium concentration of 13 at. % under pumping at 980nm
Fabrication and spectroscopy of erbium doped gallium lanthanum sulphide glass fibres for mid-infrared laser applications
No full textGallium lanthanum sulphide based glasses are proposed as high quality hosts for rare-earth doped, mid-infrared fibre lasers, that would offer compact and rugged sources for gas sensing, atmospheric transmission, and medical applications. The infrared emission spectroscopy of erbium doped glasses and fibres shows the potential of this glass host for the above applications. Mid-infrared transitions at 2.0, 2.75, 3.6, and 4.5µm have been detected and characterised
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
Spectroscopic data of the 1.8, 2.9 and 4.3µm transitions in dysprosium-doped Ga:La:S glass
No full textInfrared emission at 1.8, 2.9, and 4.3 µm is measured in dysprosium-doped gallium lanthanum sulfide (Ga:La:S) glass excited at 815 nm. Emission cross sections were calculated by Judd-Ofelt analysis, the Füchtbauer-Ladtenburg equation, and the theory of McCumber. The sigma tau value for the 4.3-µm transition is ~4000 times larger in the Ga:La:S glass than in a dysprosium-doped LiYF4 crystal, which has lased on this transition. The large sigma tau value and the recently reported ability of Ga:La:S glass to be fabricated into fiber form show the potential for an efficient, low-threshold mid-infrared fiber laser. The fluorescence peak at 4.3 µm coincides with the fundamental absorption of atmospheric carbon dioxide, making the glass a potential laser source for gas-sensing applications
Properties of dysprosium doped GaLaS fibre amplifiers operating at 1.3µm
No full textIn light of the recent progress on the fabrication of GaLaS fibres we have modelled the performance of dysprosium doped GaLaS fibre amplifiers operating at 1.3µm. Based on experimental data, we find the incorporation of a co-dopant (terbium) in the fibre core significantly shortens the optimum amplifier length from >30m to ~3m. Such a device may be practical given the fibre losses currently achieved in GaLaS fibres
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