3RD-ORDER OPTICAL SUSCEPTIBILITY OF SMALL METALLIC PARTICLES

We present a tight-binding model for the linear and non-linear optical properties of small metal particles, which takes into account both si ze and matrix effects. We show that the surface states and the dielect ric medium embedding the particles determine the properties of the mic rocrystals; in particular, we prove that the shallow-lying d-band play s a crucial role in noble-metal particles. As an example, we calculate the third-order susceptibility and the phase-conjugated signal for go ld clusters made of several hundred atoms. A good agreement with exper imental results is obtained.