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  • 1.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Lashgari, K.
    Edvardsson, Sverker
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Westin, G.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Atomically designed precursors in optical fiber amplifiers: The thermal stability of the heteroimetallic ErAl_3(OPri)_12 in a solution-coated silica soot2005In: Journal of Applied Physics, ISSN 0021-8979, Vol. 97, no 11, p. 113104-Article in journal (Refereed)
  • 2.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Comment on:"Photodarkeningin Yb-doped aluminosilicate fiber induced by 488nm irradiation"2007In: Optical Letter, ISSN 0146-9592, Vol. 33, no 11, p. 1216.-Article in journal (Refereed)
    Abstract [en]

    We present some strong evidence against the assignment of an ytterbium-related oxygen deficiency center (ODC) near 230 nm in Yb-doped aluminosilicate glass in the Letter by Yoo

  • 3.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Divalent Ytterbium in Ytterbium Doped Aluminosilicate Glass - Aspects on Photodarkening in Fiber Lasers2007In: 2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), VOLS 1-5, New York: IEEE conference proceedings, 2007, p. 1902-1903Conference paper (Refereed)
    Abstract [en]

    We show that divalent ytterbium ions are present in ytterbium doped aluminosilicate glass. The presence of Yb^2+-ions may influence the formation of induced color centers in ytterbium doped fiber lasers leading to reduced performance.

  • 4.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Materials optimization for ytterbium-doped high power fiber lasers2008In: 2008 CONFERENCE ON LASERS AND ELECTRO-OPTICS & QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE, VOLS 1-9, New York: IEEE conference proceedings, 2008, p. 232-233Conference paper (Refereed)
    Abstract [en]

    In this paper we will present paths to reduce the extent of photodarkening in ytterbium. doped fiber lasers based on the aluminosilicate glass matrix. This will enable higher powers and longer operating lifetimes.

  • 5.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Preventing Photodarkening in Ytterbium-Doped High Power Fiber Lasers; Correlation to the UV-Transparency of the Core Glass2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 2, p. 1260-1268Article in journal (Refereed)
    Abstract [en]

     

    Photodarkening experiments are performed on ytterbium-doped silicate glass

    samples. A strong charge-transfer (CT) absorption band near 230nm in

    aluminosilicate glass is found to be correlated to the mechanism of induced

    color center formation. Excitation into the CT-absorption band generates

    similar color centers as observed in ytterbium-doped fiber lasers under

    915nm high power diode pumping. The position of the CT-absorption band is

    compositional dependent and is shifted to shorter wavelengths in ytterbium

    doped phosphosilicate glass. Very low levels of photodarkening is observed

    for the ytterbium doped phosphosilicate glass composition under 915nm high

    power diode pumping. Possible excitation routes to reach the CT-absorption

    band under 915nm pumping are discussed.

     

  • 6.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. Acreo FiberLab, Sweden.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Reduction of photodarkening in Yb/Al-doped fiber lasers2008In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2008, p. U269-U276Conference paper (Refereed)
    Abstract [en]

    A strong charge-transfer band at UV-wavelengths is found to play a major role for the observed induced optical losses (photodarkening) in ytterbium doped high-power fiber lasers. This is correlated to the valence stability of the ytterbium ion in the silicate glass matrix, which we believe is the origin of photodarkening. We have performed UV-irradiation experiments on ytterbium-doped preform samples and accelerated photodarkening experiments on Yb-doped fibers, by using 915nm high power diodes. Our results show that photodarkening can be reduced, to low levels, either by preparing the preform glass in a reducing atmosphere or by hydrogen loading the fiber in a pressure chamber at room temperature.

  • 7.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Strong UV absorption and visible luminescence in ytterbium-doped aluminosilicate glass under UV excitation2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 22, p. 3352-3354Article in journal (Refereed)
    Abstract [en]

    A broad visible luminescence band and characteristic IR luminescence of Yb3+ ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f�d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d�4f emission from Yb2+ ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers.

  • 8.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edvardsson, Sverker
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Lashgari, K.
    Uppsala University.
    Westin, G.
    Uppsala University.
    A structural investigation of a synthesized precursor for fiber optical applications; the heterobimetallic ErNb_2(OPr^i)_132006In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 29, no 4, p. 386-391Article in journal (Refereed)
    Abstract [en]

    A structural investigation of a synthesized precursor in a silica glass matrix is performed. Silica soot samples are doped with the heterobimetallic precursor ErNb2(OPri)13 by using a conventional solution doping technique and heat treatments to different temperatures. The precursor has also been introduced into a silica fiber preform by using the modified chemical vapor deposition technique. Analyses are made by using ultraviolet–visible–near infrared absorption spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and powder X-ray diffraction. It is concluded that an immiscible system of ErNbO4 crystallites and Nb2O5 is formed in the silica soot samples at high temperatures. Colloidal particles of ErNbO4 are also formed in the silica glass fiber preform showing interesting features.

  • 9.
    Engholm, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Vanin, E
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Characterization of Erbiuim Crystallites Embedded in Silica GlassManuscript (Other (popular science, discussion, etc.))
  • 10. Lashgari, K
    et al.
    Kritikos, M
    Engholm, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norin, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edvardsson, Sverker
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Westin, G
    Sol-gel preparation of Er-doped planar and fibre wave-guides using heterometallic2006In: SPIE conference, San Diego (2006)., 2006Conference paper (Other academic)
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