Ultrafast optical properties of gold nanoshells

We present the results of ultrafast pump-probe measurements on films of gol d-coated gold sulfide nanoshells. The measured change in transmission (Delt a T/T) agrees with theoretical calculations that relate the increase in the electron temperature to changes in the Drude and interband components of t he gold shell dielectric function. The major contribution physically corres ponds to modified screening of the d-band electrons by the conduction elect rons in the gold shell. The electrons cool with a lifetime of similar to 1. 6 ps, indicating a slower cooling rate than is observed in bulk gold. (C) 1 999 Optical Society of America [S0740-3224(99)02710-1].