Enhanced Nonlinear Saturable Absorption of MoS₂/Graphene Nanocomposite Films

Abstract

MoS2/graphene nanocomposite films are fabricated by vacuum filtering with liquid-phase exfoliated MoS2/graphene suspension. The nanocomposite films are characterized by Raman spectroscopy, UV–vis spectroscopy, and atomic force microscopy, indicating the optical films with a large scale and high optical homogeneity. The enhanced saturable absorption of MoS2/graphene nanocomposite films compared with pristine MoS2 film and graphene film is investigated using an open-aperture Z-scan technique with a femtosecond laser at 800 nm. The nonlinear absorption coefficient of MoS2/graphene nanocomposite film is ∼ −1217.8 cm/GW, which is larger than that of MoS2 film (∼ −136.1 cm/GW) and graphene film (∼ −961.6 cm/GW) at the same condition. The imaginary part of the third-order nonlinear optical susceptibility of the nanocomposite film can reach Imχ(3) ∼ 10–9 esu with a figure of merit ∼10–14 esu cm, low saturable intensity (∼157.0 GW/cm2), and high modulation length (∼32%). A coupling model is considered in order to understand the nonlinear absorption properties of MoS2/graphene nanocomposite films, which suggest the enhancement can be attributed to charge transfer between MoS2 and graphene. The results pave the way for the design of nonlinear optical properties with two-dimensional materials for good performance of optical switches or mode lockers based on saturable absorbers.