SURFACE-PLASMON ENHANCED 2ND-HARMONIC RESPONSE FROM GOLD CLUSTERS EMBEDDED IN AN ALUMINA MATRIX

The second order nonlinear response from 4 nm diam gold clusters embed ded in an alumina matrix deposited on a pure silica substrate has been recorded as a function of the wavelength of the fundamental incident beam. The spectrum exhibits a narrow resonance band peaked at 520 nm a s a result of the coupling of the second harmonic field with the surfa ce plasmon of the particles. The nonlinear second harmonic response of gold clusters is found to be blueshifted compared to the bulk, due to the finite size effects on the cluster optical properties, as already observed with the linear response. Furthermore, this nonlinear respon se appears to be well described with a simple free electron model wher e the valence electrons only participate through the screening of the ionic cores, owing to the weakness of the interband transition contrib ution. (C) 1998 American Institute of Physics. [S0021-8979(98)01820-9]