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.