Length distributed measurement of temperature effects in Yb-doped fibers during pumping

We demonstrate a distributed measurement technique to observe temperature changes along pumped Yb-doped fibers. This technique is based on an array of fiber Bragg gratings acting as a temperature sensor line. The Bragg gratings are inscribed directly into the Yb-doped fiber core using high-intensity ultrashort laser pulses and an interferometric setup. We studied the temperature evolution in differently co-doped Yb fibers during optical pumping and identified different effects contributing to the observed temperature increase. We found that preloading of fibers with hydrogen supports the formation of Yb2+ during UV irradiation and has a large impact on fiber temperature during pumping. The proposed technique can be applied to investigate the homogeneity of pump absorption in active fibers and to support spatially resolved photodarkening measurements

Interregionalism's impact on regional integration in developing countries: the case of Mercosur

This article examines the impact of interregionalism on deepening regional integration processes in non-European Union (EU) regions, specifically the Southern Common Market (Mercosur). It considers whether ‘capacity-building’ functions of interregionalism are present in EU–Mercosur relations. It argues that although negotiations for an association agreement might have helped Mercosur survive periods of severe crisis in the past, the terms of the agreement under negotiation were not sufficiently attractive to encourage deeper integration in Mercosur. Moreover, interregionalism cannot be expected to compensate for low institutionalization, nor substitute for weak political willingness to deepen integration. Ultimately, Mercosur alone can decide how far it wants to take its regional integration

High-energy soliton pulse generation with a passively mode-locked Er/Yb-doped multifilament-core large-mode-area fiber laser

The generation of high-energy pulses from rare-earth-doped fiber lasers has been under intense investigation for the past few years. The pulse energy achievable in mode-locked fiber laser systems is limited by nonlinear effects occurring during propagation through the fiber, mainly Kerr-nonlinearity, avoid self-consistent pulse evolution inside a fiber laser resonator and hinder the pursuit of higher pulse energies from mode-locked fiber lasers. Hence, the employment of low-nonlinearity large-mode-area fibers (LMA) opens the possibility of energy scaling. This has been demonstrated recently by a femtosecond ytterbium-doped fiber laser operating in the anomalous net-cavity dispersion regime emitting a pulse energy as high as 16 nJ. More recently, single-mode operation for high energy amplification in the 1.5 mum wavelength region has been demonstrated based on a multifilament core fiber combining large area and high doping concentration