Ultrafast relaxation dynamics of electrons in silver nanocrystals embedded in glass

Relaxation dynamics of excited electrons in silver nanocrystals with average radii of 3.0 and 4.9 nm embedded in glass has been investigated by femtosecond pump and probe spectroscopy. The surface-plasmon band shows both broadening and red shift with excitation by 200 fs laser pulses. Time response exhibits a two-component decay, and the decay times of the fast and slow components are 2-3 ps and similar to 200 ps, respectively. Time evolution of the nonlinear absorption due to surface-plasmons reflects a cooling process of hot electrons through the electron-phonon interaction. The additional broadening is ascribed to the increase of surface-plasmon damping due to nonequilibrium heating of electrons. When an absolute value of a dielectric constant of silver nanocrystals is decreased with the femtosecond pulse excitation, the surface-plasmon resonance shows a red shift. We demonstrate time response of nonlinear refractive index on the picosecond time scale. (C) 1998 Elsevier Science B.V. All rights reserved.