Cavity-enhanced large third-order optical nonlinearity in AuNRs/ITO/Au plasmonic nanostructures

A sandwich plasmonic nanostructure (AuNRs-ITO-Au) composed of randomdistributed gold nanorods (AuNRs) film, indium tin oxide (ITO) space layer, and gold thin film was prepared by using sputtering methods. Third-order optical nonlinearities were investigated by using the Z-scan technique under ultralow excitation laser powers. Fifteen times of third-order optical susceptibility (chi(3)) enhancement has been obtained in AuNRs/ITO/Au compared to pure AuNRs at 880 nm. The FDTD simulation demonstrates that this enhancement is due to the further confinement of the electric field inside the sandwich nanostructure. The results are significant and may find applications in ultralow-power all-optical switches and plasmonic waveguides.