-graphene oxide for ultrafast third-order nonlinear optical response

Third-order nonlinear optical absorption of light by materials is weak due to its perturbative nature, although a strong nonlinear response is crucial to applications in optical limiting and switching. A complex few-layer VSe₂/graphene oxide (GO) hybrid with strong interlayer coupling was prepared by a facile hydrothermal method. In this strongly coupled VSe₂/GO, we demonstrate experimentally and theoretically a strong ultrafast excited-state absorption (ESA) that is in stark contrast to the saturable absorption of semi-metallic VSe₂ and a weak two photon absorption of GO. Due to the extremely efficient charge transfer at ultrafast time scales between VSe₂ and GO, we observed the enhancement in the third-order nonlinear optical absorption by orders of magnitude compared to VSe₂ that shows saturable absorption and one order of magnitude compared to GO. Spectroscopic evidence of our study indicates that the optical signatures of VSe₂ and GO are modified in the hybrid, displaying direct coupling of both domains. To explain the results, we develop a rate-equation and numerically simulate the results. Using the strong ESA of our hybrid materials, we fabricate liquid cell-based high-performance optical limiters with important device parameters better than benchmark optical limiters.