Improved third-order optical nonlinearity and optical limiting behaviour of (nanospindle and nanosphere) zinc ferrite decorated reduced graphene oxide under continuous and ultrafast laser excitation

Abstract

Nanohybrids consisting of uniform nanospheres and nanospindles of zinc ferrite attached to reduced graphene oxide were prepared by hydrothermal reaction. Zinc ferrite decorated reduced graphene oxide exhibited enhanced nonlinear absorption, refraction and optical limiting (OL) action under continuous wave (532 nm, 50 mW) and ultrafast (800 nm, 150 fs) excitation. The enhancement can possibly be attributed to the synergistic effect stemming from the observed reverse saturable absorption and self-defocusing in the material. The role of defects in improving the nonlinear optical (NLO) performance of ZnFe₂O₄–rGO was explained with the aid of Raman spectroscopy and ground state absorption studies. Using fs and cw excitation, the estimated nonlinear absorption coefficient [γ_3PA(fs) = 4.0 × 10⁻¹² m W⁻¹, β_(cw) = 6.5 × 10⁻⁵ m W⁻¹], nonlinear refractive index [n_2(fs) = 4.2 × 10⁻¹⁸ m² W⁻¹, n_2(cw) = 4.7 × 10⁻¹² m² W⁻¹] and third order nonlinear optical (NLO) susceptibility [χ ⁽³⁾ _(fs) = 1.9 × 10⁻¹⁵ esu, χ ⁽³⁾ _(cw) = 4.2 × 10⁻⁶ esu] of nanospindle ZnFe₂O₄–rGO were found to be higher than those of its other counter parts. The estimated NLO parameters were found to be higher than those of other known OL materials such as functionalized hydrogen exfoliated graphene, CdO. Thus zinc ferrite decorated rGO nanostructures with proficient NLO coefficients have potential scope for utilizing them as smart materials for OL applications.