The nonlinear optical response of gold films of different thicknesses is investigated by two-beam second-harmonic
generation to address the role of surface and bulk effects in their second-order nonlinear optical response. Preliminary
results suggest that both types of effects contribute to the measured second-harmonic signals. Furthermore, both effects
are found to be enhanced for the thin film with a higher level of nanoscale surface roughness.
The nonlinear refraction index <i>n<sub>2</sub></i> and the reverse saturation absorption (RSA) coefficient β of a series of hydroxylphenyl porphyrin have been measured using single beam Z-scan technique with a 8 ns laser pulse at 532nm and the third-order nonlinear susceptibility χ<sup>(3)</sup> of the samples are calculated. It is seen that a series of hydroxylphenyl porphyrin have large value of the reverse saturation absorption and cubic nonlinear refraction. The effects of molecular structures on the third-order nonlinear optical properties were discussed. Experimental results show that the effects of different numbers and different positions of substituent to the nonlinear refraction of porphyrin are evident.