Defect engineering of Y2Ti2O5S2 two-dimensional material for broadband ultrafast lasers

In this paper, a novel broadband two-dimensional material was investigated and applied in ultrafast solid-state lasers. For comparison, Y₂Ti₂O₅S₂-SSR and Y₂Ti₂O₅S₂-Mg were synthesized by solid-state reaction (SSR) method and Mg-doped flux approach respectively. Based on the calculation of first principles, the bandgap width of Y₂Ti₂O₅S₂-Mg (YTOS-Mg) was greatly reduced by introducing S–Mg–S layer defects. Microstructural characterization confirmed morphological changes in YTOS-Mg. Nonlinear optical response experiment further demonstrated YTOS-Mg possessed a lower saturation intensity and higher modulation depth than Y₂Ti₂O₅S₂-SSR (YTOS-SSR), which are two significant indicators for optical modulators in laser resonator. The YTOS-Mg was first fabricated as saturable absorber and applied in all-solid-state lasers. Q-switched mode-locking lasers with minimum pulse widths 149 ps and 1.4 ns were generated in 1 μm and 2 μm region. The experimental results indicate the YTOS-Mg is a novel broadband saturable absorber. It exhibits significant potential for applications in ultrafast lasers generation.