The acoustic vibrational modes of Au nanorods with aspect ratios between 2.1 and 5.5 have been investigated by timeresolved
spectroscopy. The results show that laser excitation launches a coherent vibrational motion which has a period that depends linearly on the length of the rod. Due to polydispersity in the samples, the measured period also depends on the probe wavelength (i.e., for a given sample different probe wavelengths interrogate different length rods). Analysis of the data potentially provides information about the elastic properties of these unique materials.