Giant femtosecond nonlinear optical response in bi-metallic GO nanocomposites for photonic applications

Graphene based 2D materials after suitable modification may results into materials with strong nonlinear optical (NLO) responses. Here, incorporation of Au, and Ag nanoparticles (NPs) in graphene oxide (GO) nanosheet (GO_Au_Ag) is carried out for restructuring of its electronic bands. Reshuffling in the electronic band-to-band transitions and their relaxation process is achieved resulting into achievement of high NLO response in GO_Au_Ag than those of pure GO nanosheets, graphene quantum dot (GQD), and nitrogen doped GQD (N-GQD), by fs Z-scan technique. GO, GQD, and N-GQD, shows only two-photon absorption (2PA), with two times larger absorption coefficient (β) in N-GQD than that of GO and GQD. Interestingly, GO_Au_Ag nanocomposite exhibits simultaneous 2PA and three-photon absorption (3PA) under the excitation of the fs laser pulses. In the presence of prolongated relaxation time and transfer of charge between GO and metal's state through excited state absorption (ESA), GO_Au_Ag showed a larger β value than N-GQD and the giant third order nonlinear susceptibility (χ ⁽³⁾) of ∼10⁻⁹ (esu). Furthermore, GO_Au_Ag sample shows the optical limiting threshold of only 4.6 μJ/cm², smaller than that of N-GQD.