Intercalating-induced second-harmonic generation in centrosymmetric multilayer graphene

Second-harmonic generation (SHG) is a nonlinear optical process, where two incident photons coherently combine into one photon with double the energy, which is important for laser frequency conversion. Graphene has huge potential in various on-chip optical applications including laser sources, waveguide structures, and detection-sensitive units. However, efficient SHG is commonly present in systems with broken inversion symmetry but absent from centrosymmetric structures such as graphene. The study of graphene SHG signal has gradually become a hot research topic. In our work, H2SO4-intercalation tunable method was developed to tune the lattice distortion of multilayer graphene and lead to charge transfer from graphene layers to H2SO4 molecules. Thus, noncentrosymmetric electric dipoles can be acquired and enhance SHG response. Furthermore, the change of SHG is reversible after deintercalation, because the lattice distortion can be restored. Our research on the intercalating-induced SHG effect may lead to a better design of graphene-based nonlinear optical devices in the future.