Femtosecond optical investigation of electron–lattice interactions in an ensemble and a single metal nanoparticle

Electron–lattice energy exchange is investigated in an ensemble of silver nanoparticles of mean diameter 9 nm and in a single 30-nm particle using a femtosecond pump–probe technique. The dependences of the measured transient transmission change and of the electron energy loss kinetics on the excitation amplitude are compared to the results of numerical simulations of nonequilibrium electron relaxation and of the two-temperature model. The good agreement between the theoretical and experimental data indicates that, for the studied low particle density samples, hot-electron cooling is dominated by electron–lattice coupling in a nanoparticle both for weak and large electron heating with a minor influence of their surrounding environment (glass or polymer matrix). PACS 78.47.+p; 42.65.-k; 73.20.Mf