Ultrafast study of electron–phonon coupling in colloidal gold particles

The hot electron dynamics in 11±2 nm diameter Au particles has been examined by transient absorption and bleach recovery measurements. These experiments show that the timescale for energy relaxation by electron–phonon coupling decreases as the pump laser power decreases, and that the relaxation time is independent of the pump or probe wavelength at low pump power. The electron–phonon relaxation time measured in our experiments (∼650 fs) is very similar to the time constant obtained from experiments with bulk gold samples. These observations are explained using the two-temperature model for electron–phonon coupling.