Ultrafast dynamics of nonequilibrium electrons in a gold nanoparticle system

Transient absorption spectra were measured to investigate the nonlinear response of a gold nanoparticle system by the femtosecond pump-probe method. We obtained temporal changes of electron temperatures and effective damping constants by fitting transient absorption spectra with Mie scattering theory. In the ultrafast region, the nonlinear response originates mainly from the hot electron system which is heated by the incident pump pulse. It is noteworthy that the lattice temperature plays an important role even in the first step of the nonlinear response through the change of the effective damping constant. In the long-time-scale region, over 10 ps, both the electron and the lattice temperatures contribute to the nonlinear response comparably. The origin of the effective damping constant is also discussed with the surface scattering and the $e-p$scattering processes.