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We propose a numerical method to evaluate the two-photon-induced luminescence (TPL) of single gold nanorods (GNRs). The validity of this method is confirmed by the cos4 α dependence of the TPL of single GNRs on the polarization angle α, which is in good agreement with experimental observations. As comparing with their linear optical properties such as scattering and absorption, the TPL of a single GNR is found to be more sensitive to the change of the surrounding environment. This property is exploited to detect nanoparticles (NPs) approaching the GNR from a far place. By monitoring the evolution of the TPL on the distance between the GNR and a NP, it is possible to extract various information on the NP, including the moving direction, position, size, and material type. For GNRs whose extinction is dominated by absorption, the response and sensitivity are found to depend strongly on their sizes. The detection of the nonlinear optical responses of GNRs may find potential applications in the fields of nanophotonics and biophotonics.

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