Optical properties and coherent vibrational oscillations of gold nanostars

Hot electron relaxation and coherent vibrational oscillations of gold nanostars (AuNS) were studied using femtosecond laser spectroscopy. Transient profiles feature a fast decay attributed to electron-phonon interaction and a slower decay due to phonon relaxation. Superimposed on the slow decay are oscillations attributed to coherent vibrations of the AuNS with a period dependent on probe wavelength, due to size variation of the AuNS. In addition, persistent spectral hole-burning studies indicate depletion of AuNS at the excitation wavelength and formation of redder-absorbing AuNS aggregates. In conjunction with experiments, theoretical calculations were carried out to gain insight into the coherent vibrational oscillations.