Ultraviolet laser induces color centers in ytterbium-doped silica glasses

Ytterbium-doped silica fiber (YDF) has important applications in material processing and scientific research. The photodarkening (PD) effect, which originates from the formation of color centers, can decrease the laser output power over 1,000 h by about 10% and will seriously restrict the power stability of the fiber laser. However, the nature of the PD color centers has not been adequately elucidated until now.

In a recent study, a team from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences has made a systematic study of PD color centers in YDF. Related work was published in the Journal of Non-Crystalline Solids.

In their experiment, a series of YDF core glasses were irradiated with a 193 nm ArF excimer laser for different durations. The species of the UV laser-induced color centers were identified by radiation-induced absorption (RIA), in-situ photoluminescence (PL), and continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopic techniques.

They found that the oxygen hole center and the Yb₂⁺ ion pairs were primarily responsible for the UV laser radiation-induced darkening, and their formation was highly dependent on the charge balance between the Yb₃⁺ ion and its ligand.

The study also showed that for the Yb₃⁺/Al₃⁺ co-doped silica glass, the Yb₃⁺ ions were surrounded by electronegative [AlO_4/2] and electroneutral [SiO_4/2]⁰ groups, and the electronegative [AlO_4/2] group favored the formation of the Yb₂⁺ and Al-OHC pairs.