Abstract
The formation and bleaching of color centers during annealing of pre-darkened ytterbium-doped silica fibers is modeled by three-electron bond (TEB) = Si<O(2):∙Yb absorption centers. The nature of a center and underlying mechanism for its annealing in formation, shift and dissociation of chemical bonds is described in terms of a Markov statistical model with state change set by Bose-Einstein phonon statistics. The center hold one terminal and four active states with activation energies for transitions among these found to match bond energies of molecular oxygen in ionic character bonds of 1 and 1½ bond order. Experimentally observed in- and decrease in absorption during ramp and isothermal annealing of pre-darkened ytterbium co-doped silica fibers are hereby matched by a set of = Si<O(2):∙Yb centers.
Highlights
The long term stability of amplifiers and lasers is critically influenced by photodarkening (PD) with time dependent broadband loss centered at visible wavelengths and a long tail extending into the near infrared
Al-P 0.08 A|A|Y 0.210 In Table 1 the average ionic character of the three-electron bond (TEB) within a tetrahedral or octahedral unit is given by the geometric average of the individual links. This is a consequence of the two states for each TEB which leads to formation of resonant spin paired TEB↓ to TEB↑ bonds for Yb|P, Yb|Al or Yb|Yb edge connections while the TEB to Si
It is proposed that the PD color centers are due to a σ-bond (“1”) in parallel to a three electron bond (TEB) to Yb as “1+TEB” formed on = Si
Summary
The long term stability of amplifiers and lasers is critically influenced by photodarkening (PD) with time dependent broadband loss centered at visible wavelengths and a long tail extending into the near infrared. In [3] Yb/Al co-doped preform material show 220 nm (5.63 eV) absorption and excitation by 488 nm light which leads to broadband PD loss as well as increased 220 nm absorption This result is in [3] explained by Yb ions preferably occupying oxygen-surrounding voids created by Al with tetrahedral or octahedral coordination. To distinguish the different mechanisms involved in the PD process it appears advantageous to analyze the bleaching of pre-darkened fibers by annealing as the relaxation reaction hereby only relies on fiber temperature. This opens for the possibility to directly relate observed change in absorption with activation energy. This model gives good match to the annealing data from [11,12,13] for a distributed set of CC sites of individual TEB polarization
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
