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Nonlinear response of gold nanoparticles embedded in glass matrix

Small metal particles embedded in glass matrix has been investigated energetically both in the application research field and in the basic research field, since the strong enhancement of the third-order nonlinear optical susceptibility is observed around the peak of the surface-plasmon resonance. The mechanism of the nonlinear response, however, has not been clarified yet. We measured transient absorption spectra to investigate the nonlinear response of the gold nanoparticle system by the femtosecond pump-probe method. It is concluded that the nonlinear response originates mainly from the hot electron which is raised by the incidence of the pump pulse in sub-picosecond region. In the long time-scale region, where the time resolution is longer than 5~ps, transient change of the lattice temperature plays an important roll of the nonlinear response.