Study of Electron−Phonon Coupling Dynamics in Au Nanorods by Transient Depolarization Measurements

Electron−phonon (e-ph) coupling dynamics in Au nanorods are studied with femtosecond transient depolarization experiments. Au nanorods exhibit strongly anisotropic e-ph coupling dynamics. It is considered to arise from different weights of pump energy assigned to two polarization directions because of the anisotropy of Au nanorods rather than because of an intrinsic process. The e-ph coupling kinetics measured by transient experiments cannot be simply described by a single exponential function but by the integral of components contributed by random distribution of Au nanorods at all directions in aqueous solution. After this correction, the relationship between electron−phonon relaxation times and pump power is linear even in relatively high power. The time extrapolated to zero intensity is 0.75 ps, which is similar to the characteristic electron−phonon coupling time for nanodots and bulk Au.