Large third-order optical nonlinearity and ultrafast optical response in thin Au nanodisks

Nanostructures with remarkable optical nonlinearity and ultrafast light response have enabled numbers of applications in the fields varying from physics to biochemistry, and even quantum science. Maximally increasing the optical nonlinearity and simultaneously reducing the light response time of nanostructure is regarded as a great challenge for the optics from both fundamental and applied. In this paper, we report unprecedentedly huge third-order nonlinearity and ultrafast property in the nanosystem of Au nanodisks with ∼7 nm thickness. Their thin thickness brings about large electric field enhancements, leading to the third-order nonlinearity susceptibility (χ(3)) reaching the order of 10−18 m2/V2 (∼10−10 esu), which is 1-3 orders of magnitude larger than that of other shapes of Au nanostructures in the same solution environment, such as nanospheres, nanorods and triangle nanoprisms. Furthermore, optical Kerr measurements demonstrate their optical response time is as fast as ∼100 fs. Our findings demonstrate the thin Au nanodisk can be a suitable candidate for ultrafast nonlinear optical devices, such as the all-optical switches and all-optical signal processing devices.