Wavelength-Dependent Nonlinear Optical Absorption and Broadband Optical Limiting in Au-Fe₂O₃-rGO Nanocomposites

Broadband optical limiting and wavelength-dependent nonlinear absorption studies of Au-Fe2O3-(15, 25, 40 wt %)rGO (reduced graphene oxide) nanocomposites were investigated using the Z-scan technique and excited with femtosecond (700–900 nm, 80 MHz, 150 fs) laser pulses. A reduction in the graphene perfect (La) domain and ID/IG ratio observed in the Raman data and the appearance of a Au 4f and Fe 2p singlet along with a shift in the C 1s state toward higher energy in the XPS data, peak broadening in the XRD data, and different mass residues left out with respect to content of rGO in the TG-DTA data strongly indicated the incorporation of Au-Fe2O3 nanostructures on solar exfoliated reduced graphene oxide. Selected aread electron diffraction data ascertained the presence of Au and Fe2O3 as a composite, and transmission electron microscopy (TEM) data revealed that the nano-octahedra Au-Fe2O3 turned themselves into nanospindles during incorporation of rGO. Ground state absorption spectra illustrated a pure and composite system possessing a broad absorption in the UV–visible spectral region which suffered band structure alteration with respect to its morphology. All the samples exhibited reverse saturable absorption (RSA) and broadband optical limiting action. The RSA has been attributed to the presence of a two-photon absorption (2PA) process. As wavelength increased, the 2PA coefficient also increased and was found to be varying in the order of Au-Fe2O3-rGO > Au-Fe2O3 > rGO. The higher 2PA coefficient (16.0 × 10–10 m/W) and lower onset-optical limiting threshold (22.01 μJ/cm2) of Au-Fe2O3-(15 wt %)rGO is attributed to the higher loading content of Au-Fe2O3, extent of conjugation due to reduction, higher ID/IG ratio and 1D (nanospindle) structure. Our results suggest that the Au-Fe2O3-(15 wt %)rGO nanocomposite is promising for broadband optical limiting applications to protect sensitive detectors (including human eyes) from high-power, near-infrared, ultrafast, laser-pulse-induced damage.