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Effective mitigation of photodarkening in Yb-doped lasers based on Al-silicate using UV/visible light

: Piccoli, Riccardo; Robin, Thierry; Méchin, David; Brand, Thomas; Klotzbach, Udo; Taccheo, Stefano


Ramachandran, S. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Fiber Lasers XI. Technology, Systems, and Applications : 3 - 6 February 2014, San Francisco, California, United States
Bellingham, WA: SPIE, 2014 (SPIE Proceedings 8961)
ISBN: 978-0-8194-9874-8
Paper 896121
Conference "Fiber Lasers - Technology, Systems, and Applications" <11, 2014, San Francisco/Calif.>
Conference Paper
Fraunhofer IWS ()
optical fiber; photobleaching; photodarkening; Yb-fibre laser

In this work we discuss the impact of visible light radiation on photodarkening generation in 1070-nm Yb-doped fiber lasers. Simultaneous photodarkening and photobleaching effects induced by 976 nm and 405 nm or 550 nm radiations respectively were investigated. We observed a significant photobleaching effect due to 405 nm radiation but not a complete recovery. A strong absorption of the 405 nm radiation by the excited ions (Excited-State Absorption) was also observed and found as a main limiting factor for the bleaching performance together with observation of photodarkening losses induced by ground-state absorption. To proper define the optimum bleaching wavelength we report, for the first time to the best of our knowledge, the Excited-State Absorption cross section in the visible range. The reported experiments allow to individuate the main parameters defining the optimum bleaching wavelength. In a final experiment, using optimized 550-nm wavelength bleaching radiation, we were able to operate a laser at 93% of its pristine power level compensating a power drop of about 45% in absence of bleaching. The method we present is an effective yet simple way to run laser using standard Al-silicate fibers with doping level over 1026 ions/m3 and high inversion.