LARGE AND EXTREMELY FAST THIRD-ORDER NON-LINEARITY OF Ag NANOPARTICLES EMBEDDED INTO A Cs_xO SEMICONDUCTOR MATRIX

The third-order optical nonlinearity of Ag-O-Cs thin films, where Ag nanoparticles are embedded into a Cs_xO semiconductor matrix, was measured by the femtosecond optical Kerr technique. The third-order nonlinear optical susceptibility, \chi⁽³⁾, of the thin films was estimated to be 1.1×10^-9 esu at the incident wavelength of 820 nm. The response time, i.e. the full width at half-maximum of the Kerr signal, is as fast as 114 fs only. The intrinsic third-order optical nonlinearity can be attributed to the intraband transition of electrons from the occupied state near the Fermi level to the unoccupied state. It is suggested that such a nonlinearity is further enhanced by the local field effect that is present in the metallic nanoparticles composite thin films.