The surface plasmon damping induced by high excitation of the electron gas is studied in femtosecond pump-and-probe experiments on gold colloids embedded in a sol-gel matrix. Optical excitation of single-particle interband transitions leads to a pronounced broadening of the surface plasmon line. A similar behavior is observed for resonant excitation of the surface plasmon. This broadening is the dominant optical nonlinearity of the system, and reflects the excitation-induced damping of the surface plasmon resonance. The time evolution of the damping rate follows that of the electronic scattering rate. [S0031-9007(97)02694-X]

Femtosecond white-light experiments on Au-colloids embedded in a sol-gel matrix show that excitation of single-particle interband transitions leads to an initial plasmon-line-broadening caused by electron scattering.

The optical absorption of a bulk metal is spread over a wide spectral range. In contrast, colloids consisting of the same metal show narrow absorption resonances [1]. This spectral compression of the oscillator strength is due to enhanced optical coupling to the surface plasmon modes of spherical metal particles. E.g., the transmission spectrum of a gold-film does not show clear plasmon resonances, whereas the visible absorption spectra of gold-colloids embedded in dielectric matrices are dominated by the surface plasmon resonance lying at slightly lower energy than the onset of single-particle interband transitions.