Enhanced broadband nonlinear optical response of TiO2/CuO nanosheets via oxygen vacancy engineering

Cupric oxide (CuO), as a transition metal oxide (TMO) semiconductor, has attracted tremendous attention for various applications. In the present work, we synthesize the CuO nanosheets modified by TiO2 nanoparticles via a facile, non-toxic two-step method. Subsequently, the morphology and the structures of CuO and TiO2/CuO nanocomposites are investigated. By utilizing the common Z-scan technology, broadband nonlinear optical (NLO) properties of the as-prepared CuO nanosheets and TiO2/CuO nanocomposites are demonstrated, elucidating the enhancement on the NLO response via the TiO2 dopant, which is attributed to the more oxygen vacancies and the formed p-n junctions. Furthermore, CuO nanosheets and TiO2/CuO nanocomposites are implemented to the passively Q-switched bulk lasers operating in the near-infrared (NIR) region, generating broadband ultrastable pulses. Ultimately, TiO2/CuO nanocomposites were intergrated in a passive mode-locking bulk laser for the first time, achieving stable mode-locked pulses and verifying its ultrafast optical response potential. Our results illustrate the tremendous prospects of the CuO nanosheets modified by oxygen vacancy engineering as a broadband NLO material in ultrafast photonics field.