Ultrafast response of nonlinear refractive index of silver nanocrystals embedded in glass

Ultrafast Kerr-type nonlinearities and relaxation dynamics of photoexcited electrons in silver nanocrystals embedded in glass have been investigated by means of femtosecond pump and probe spectroscopy. The transient absorption spectrum induced by the surface plasmon excitation shows a redshift and broadening of the surface plasmon band. The additional broadening is ascribed to the increase of surface plasmon damping and the redshift originates from a change in the real part of the dielectric function of the silver nanocrystals due to nonequilibrium electron heating. The observed redshift yields the nonlinear refractive index $n_2$ of ${\text{+2.4×10}}^{\text{−10}}$ esu and its time response is 1.9 ps.