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Author: Rothhardt, M. × End date: 2022 × End date: 2014 × Start date: 2014 × DDC: 620 × Type: Text × Version: publishedVersion × WGL Institute: IPHT ×

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    Length distributed measurement of temperature effects in Yb-doped fibers during pumping
    (Bellingham : SPIE, 2014) Leich, M.; Fiebrandt, J.; Schwuchow, A.; Jetschke, S.; Unger, S.; Jäger, M.; Rothhardt, M.; Bartelt, H.
    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.
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    An electron beam profile instrument based on FBGs
    (Basel : MDPI AG, 2014) Sporea, D.; Stǎncǎlie, A.; Becherescu, N.; Becker, M.; Rothhardt, M.
    Along with the dose rate and the total irradiation dose measurements, the knowledge of the beam localization and the beam profile/energy distribution in the beam are parameters of interest for charged particle accelerator installations when they are used in scientific investigations, industrial applications or medical treatments. The transverse profile of the beam, its position, its centroid location, and its focus or flatness depend on the instrument operating conditions or on the beam exit setup. Proof-of-concept of a new type of charged particle beam diagnostics based on fiber Bragg gratings (FBGs) was demonstrated. Its operating principle relies on the measurement of the peak wavelength changes for an array of FBG sensors as function of the temperature following the exposure to an electron beam. Periodically, the sensor irradiation is stopped and the FBG are force cooled to a reference temperature with which the temperature influencing each sensor during beam exposure is compared. Commercially available FBGs, and FBGs written in radiation resistant optical fibers, were tested under electron beam irradiation in order to study their possible use in this application.