  We report ultrafast electron dynamics in gold nanorods investigated using 80
fs laser pulses centered at 1.57 eV. Five types of nanorod colloidal
suspensions in water having their longitudinal surface plasmon peak (ELSP) on
either side of the laser photon energy (EL) have been studied. For ELSP>EL,
photo-induced absorption with single decay time constant is observed. On the
other hand, for ELSP<EL, photo-bleaching is observed having biexponential decay
dynamics; the faster one between 1-3 ps and slower one between 7ps to 22ps both
of them increasing almost linearly with the difference |EL-ELSP|. These time
constants increase linearly with the pump intensity. Simulations have been
carried out to understand the interplay between photo-bleaching and
photoinduced absorption.
