Photophysics and spectroscopy of metal particles

This paper describes our recent work using ultrafast laser spectroscopy to examine the fundamental properties of metal particles. Two studies are pres ented. First, the characteristic time scale for electron-phonon coupling in Au particles with sizes between 2 and 120 nm has been examined by bleach r ecovery measurements. These experiments show that the coupling between the electrons and phonons is independent of particle size, to within the signal -to-noise of our experiments. We have also used transient absorption spectr oscopy to examine the low-frequency "breathing" modes of the Au particles. These modes are impulsively excited by the rapid lattice heating that accom panies electron-phonon coupling. The breathing motion contributes to the tr ansient absorption signal because the position of the plasmon band depends on the free electron density and, thus, the particle volume. The measured f requencies are inversely proportional to the radius, and almost exactly mat ch the predictions of classical mechanics calculations for Au.