Reversible photo-darkening and resonant photobleaching of Ytterbium-doped silica fiber at in-core 977-nm and 543-nm irradiation

• Published in: Laser physics letters 2007-10, Vol.4 (10), p.734-739
• Main Authors: Guzman Chávez, A.D., Kir'yanov, A.V., Barmenkov, Yu.O., Il'ichev, N.N.
• Format: Article
• Language: English
• Subjects: photo-bleaching; photo-darkening; Yb2; Yb3; Ytterbium fiber
• ISSN: 1612-2011; 1612-202X
• DOI: 10.1002/lapl.200710053

We report experimental results showing novel features in photo‐darkening and photo‐bleaching of a heavily‐doped Ytterbium silica fiber exposed to in‐core 977‐nm and 543‐nm irradiation. It is shown that pumping of the fiber at the resonant 977‐nm wavelength leads to an increase of absorption in the spectrally wide range (400–1000 nm, photo‐darkening) and a simultaneous decrease of the resonant (Yb3+) absorption coefficient near ∼ 1 μm (resonant photo‐bleaching). Such a character of the Ytterbium fiber spectra transformations allows us to propose that they are a signature of the 977‐nm light‐induced Yb3+ → Yb2+ conversion process, with the spectrally wide absorption, or photo‐darkening, to arise owing to the Yb2+ centers formation and the resonant photo‐bleaching to stem from the corresponding decrease of Yb3+ ions concentration. It is as well demonstrated that an exposure of the Ytterbium fiber, where the aforementioned transformations have occurred, to the 543‐nm light results in a partial return of the initial fiber properties – bleaching of the spectrally wide excess loss in the visible and increasing of the resonant 977‐nm (Yb3+) absorption peak. Therefore, we reveal a reverse process, Yb2+ →Yb3+, possibly taking place in the last case. (© 2007 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)