Optical nonlinearities of metal nanoparticle materials are one of the charactaric plasmonic properties and are strongly enhanced by the local electric field in nanoparticles around the surface plasmon resonance.  The nonlinearities are expected to be applied to optical devices of a single nanostructure.  For the design of plasmonic devices and the understanding of the origin of optical nonlinearity, it is significant to evaluate the spectrum of the nonlinear optical constants with steep changes around resonance.  Here we present the spectral dependence of third-order optical susceptibility experimentally evaluated from photo-excited transient response with pump probe method and a femtosecond laser system. The pulse width and applied electric field are 150 fs and ~5 x 10⁸ V/m, respectively. Ion implantation is one of powerful technique to fabricate nanoparticles and to control the nanostructure. The technique has an advantage of combination of metal particle and medium. Metal nanoparticle materials (Au, Ag, Cu, Ta, W...) are fabricated into substrates by 60 keV negative ion implantation at total fluences of 3-10 x 10⁶ ions/cm².  The evaluated spectra are analyzed on hot electron effect using the Maxwell-Garnett approximation with the Drude model for intraband transition and first principles calculation for interband transition.  The interband transition term in hot electron effect dominates the dispersion around the surface plasmon resonance beyond the band edge by Fermi smearing.  The large nonlinearity modulates the strength of local electric field and the nonlinear response is not proportional to input laser power.   We will discuss the power dependence of the third-order nonlinear optical response for all optical switching operation of a single nanoparticle.