Highly localized non-linear optical white-light response at nanorod ends from non-resonant excitation

We investigate gold nanorods that are excited non-resonantly using a femtosecond 800 nm pulsed laser beam. We find that they emit very localized white light--two-photon induced photoluminescence (PL)--spatially confined in the optical far-field with a full-width-at-half-maximum of 138 nm (x-y plane) and 328 nm (z-plane). The PL spectrum is characterized to show at least two components--a second-harmonic peak and an intrinsic gold interband transition.