Surface oxygen vacancies in amorphous Fe2O3 tailored nonlinear optical properties for ultrafast photonics

Fe₂O₃ nanomaterials, as one of the transition metal oxides (TMOs) materials, have garnered attention in ultrafast photonics due to their robust third-order nonlinearity, rapid carrier recovery time, high stability, broad absorption bandwidth and straightforward preparation methods. In order to further enhance the performance of Fe₂O₃ nanomaterials, oxygen vacancy defects were introduced in the process of preparing the Fe₂O₃ nanomaterials in this paper. By characterizing the nonlinear optical properties of the prepared Fe₂O₃ nanomaterials with different surface oxygen vacancy concentrations, we found that Fe₂O₃ nanomaterials with larger oxygen vacancy content have a deeper modulation depth and the larger third-order nonlinear coefficient. It also indicated that the incorporation of oxygen vacancy defects can significantly enhance the nonlinear optical properties of Fe₂O₃ nanomaterials. Furthermore, the ultrafast carrier dynamics of Fe₂O₃ materials with varying concentrations of oxygen vacancies were investigated using femtosecond-resolved transient absorption (TA) spectroscopy, elucidating the microscopic mechanism. Finally, we inserted Fe₂O₃-based saturable absorbers into Yb- and Er-doped fiber lasers. Noise-like mode-locking operation and multi-pulse mode-locking operation are realized at 1 μm in the Yb-doped fiber laser. Besides, the conventional soliton mode-locking operations with different central wavelengths are realized within 1.5 μm band in an Er-doped fiber laser.