Optical nonlinearity in glass-embedded silver nanoclusters under ultrafast laser excitation

The nonlinear optical transmission in noble metal clusters excited near the surface plasmon resonance can evolve from saturable absorption to induced absorption on varying the cluster size and applied laser fluence. Here we investigate the role of the laser pulsewidth in effecting this transition. Silver nanoclusters of sizes ranging from 2 to 6 nm, embedded in soda lime glass by the ion-exchange method, are excited with 100 fs and 300 ps laser pulses respectively. From femtosecond pump-probe measurements, the hot electron dynamics is measured in the largest cluster. Results show that thermal effects contribute to the nonlinearity in the picosecond excitation domain. Saturation intensities and effective nonlinear absorption coefficients are numerically evaluated.