Large and extremely fast third-order non-linearity of Ag nanoparticles embedded into a CsxO semiconductor matrix

The third-order optical nonlinearity of Ag-O-Cs thin films, where Ag nanopa rticles are embedded into a CsxO semiconductor matrix, was measured by the femtosecond optical Kerr technique. The third-order nonlinear optical susce ptibility, chi ((3)), of the thin films was estimated to be 1.1x10(-9) esu at the incident wavelength of 820 nm. The response time, i.e. the full widt h at half-maximum of the Kerr signal, is as fast as 114 fs only. The intrin sic third-order optical nonlinearity can be attributed to the intraband tra nsition of electrons from the occupied state near the Fermi level to the un occupied state. It is suggested that such a nonlinearity is further enhance d by the local field effect that is present in the metallic nanoparticles c omposite thin films.