Spectral mapping of the third-order optical nonlinearity of glass-metal nanocomposites

By tuning wavelengths of the femtosecond pump and probe pulses we mapped the nonlinear absorption of copper-glass nanocomposites within 520 - 620 nm range. At the pump intensity of 3 GW/cm2, the induced transmission rise was as high as 20%. The imaginary part of the third-order optical susceptibility of the nanocomposites as a function of the probe wavelength reproduced well the spectral profile of the surface plasmon resonance in copper. In contrast, the imaginary part of the third-order optical susceptibility as a function of the pump wavelength did not reproduce the plasmon profile being wider than the latter.