Measurements of high-order susceptibilities of silver nanocolloids

This experiments exploits the large sensitivity of the Z-scan technique to observe the HO response of colloids having Ag NP filling factors, between 0.23 × 10^-4 and 1.4 × 10^-4. The light source is the second harmonic of a Q-switched and mode-locked Nd:YAG laser (pulses of 80 ps at 532 nm). Single pulses at low repetition rate (10-100 Hz) are selected using a pulse-picker. The third, fifth, seventh and ninth order susceptibilities are observed for intensities between 0.1 and 1.5 GW/cm². The nonlinear refractive indices n_i (i=2,4,6,8) and the nonlinear absorption coefficients α_j (i=2,4,6,8) presented a linear dependence. This study observes the behavior of the third- and fifth-order nonlinearity as a function of the NP filling factor. The comparison of the results with predictions of an effective-medium theory enabled to understand the origin and the relative magnitude of the effective nonlinear susceptibilities.