Ultrafast optical properties of gold nanoshells

We present the results of ultrafast pump–probe measurements on films of gold-coated gold sulfide nanoshells. The measured change in transmission $(\mathrm{\Delta }T/T)$ agrees with theoretical calculations that relate the increase in the electron temperature to changes in the Drude and interband components of the gold shell dielectric function. The major contribution physically corresponds to modified screening of the d-band electrons by the conduction electrons in the gold shell. The electrons cool with a lifetime of ∼1.6 ps, indicating a slower cooling rate than is observed in bulk gold.