Abstract
Hydrogen annealing is an effective way to improve the figure of merit (FOM) of Ti:sapphire laser crystal. In this work, hydrogen annealing experiment is conducted on Ti:sapphire crystal samples with different doping concentrations, and the theoretical computation is applied to analyze the mechanism of hydrogen annealing. The experimental results show that, the annealing effects are different with the Ti doping concentrations and the polarized directions of the samples. To explain the experimental phenomenon, three kinds of Ti defect models may exist in Ti:sapphire crystal during hydrogen annealing are constructed, and their electronic and optical properties are computed. The H-Ti3+ model indicates the substitutional Ti3+ is possible to be reduced to Ti2+ and result in the decrease in α490. The H-3Ti4+-VAl3- model reveals a H atom can reduce the 3Ti4+-VAl3- defect effectively and turns it into a Ti defect similar to substitutional Ti3+, which brings increase in α490. The H-Ti3+-3Ti4+-VAl3- model shows the reduction reaction occur to the Ti4+ which face contact with Ti3+. The change of Ti3+-Ti4+ ion pair to Ti3+-Ti3+ ion pair brings the enhancement in main absorption band and suppresses the infrared residual absorption. This study is the first attempt to investigate the mechanism of hydrogen annealing on Ti:sapphire crystal in micro-level, which contributes to a deeper understanding of the annealing process and provides guidance for improving hydrogen annealing effect.
Published Version
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