Enhanced broadband optical limiting and switching of nonlinear absorption in functionalized solar exfoliated reduced graphene oxide–Ag-Fe2O3 nanocomposites

Abstract

Wavelength dependent nonlinear absorption (NLA) studies of Ag-Fe2O3–reduced graphene oxide (rGO) hybrids were performed using high-repetition rate (80 MHz), femtosecond (150 fs), and near-infrared (NIR) (700-900 nm) laser pulses. Tunable nonlinear absorption properties and broadband optical limiting performance of the pure and Ag-Fe2O3–(15, 25, and 40 wt. %) rGO nanocomposites were achieved by varying the parameters such as composition, defect states, and morphology. Detailed Z-scan experiments revealed that the NLA coefficient increases with an increase in the excitation wavelength. A switching behavior in the NLA mechanism for Ag-Fe2O3 and Ag-Fe2O3–(15 wt. %)rGO from saturable absorption (700 nm) to reverse saturable absorption (800 nm and 900 nm) was witnessed, while rGO and Ag-Fe2O3–(25 wt. % and 40 wt. %)rGO exhibited reverse saturable absorption, which is ascribed to be the 2-photon absorption (2PA) process. The origin of 2PA involves the electronic states of irregular conjugate carbon bonds based on sp2 domains of rGO for 700 nm and 800 nm excitations and surface plasmon resonance of Ag metals for 900 nm excitations. Ag-Fe2O3–(25 wt. %)rGO hybrid possesses a stronger NLA coefficient and a lower onset optical limiting threshold at all the wavelengths studied and, therefore, can be considered as a favorable candidate for broadband ultrafast optical limiters toward protection from NIR ultrashort pulse laser damages.