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

Fe 2 O 3 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 Fe 2 O 3 nanomaterials, oxygen vacancy defects were introduced in the process of preparing the Fe 2 O 3 nanomaterials in this paper. By characterizing the nonlinear optical properties of the prepared Fe 2 O 3 nanomaterials with different surface oxygen vacancy concentrations, we found that Fe 2 O 3 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 Fe 2 O 3 nanomaterials. Furthermore, the ultrafast carrier dynamics of Fe 2 O 3 materials with varying concentrations of oxygen vacancies were investigated using femtosecond-resolved transient absorption (TA) spectroscopy, elucidating the microscopic mechanism. Finally, we inserted Fe 2 O 3 -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. • Two Fe 2 O 3 materials with abundant oxygen vacancies were prepared. • Impact of oxygen vacancy concentration on their nonlinear optical properties was investigated. • Both samples possessed the ultrafast optical response. • Various mode-locking operations were achieved in the near-infrared band.