Ultrafast carrier dynamics and nonlinear absorption mechanisms in ZnO/MgO multilayered thin film

ZnO/MgO multilayered composite thin films have been prepared by spin coating method. XPS analysis verified the chemical states of Zn, Mg, and O, as well as the effective incorporation of MgO within the ZnO matrix. The linear optical studies revealed absorption features and emission pathways associated with the multilayer structure, while femtosecond, third-order nonlinear optical measurements demonstrated a pronounced reverse saturable absorption response. Femtosecond transient absorption spectroscopy was employed to probe the carrier dynamics, providing insights into ultrafast excitation, carrier trapping, and relaxation mechanisms. The optical limiting threshold (OLT) observed under femtosecond excitation indicates that the MgO/ZnO multilayer thin film exhibits excellent limiting performance. The interaction of the composite materials at the nanoscale has resulted in the superior nonlinear optical absorption (two-photon absorption) coefficient of 244.741 cm/GW as well as the limiting behavior highlighting its potential as an efficient optical limiter for ultrafast photonic applications.