Nonlinear materials with large optical nonlinearities and fast response speed are required for future photonic devices. In our research, we used a simple and sensitive method named Z-scan (single-beam) technique to measure the optical nonlinearities of liquid, solid and thin-film materials. With the Z-scan technique, both the sign and the magnitude of the nonlinear refractive indices n₂ and the magnitude of the nonlinear absorption coefficients β of a material can be found. In our experiments, we successfully applied the Z-scan technique to determine the nonlinearities of CS₂, CaF₂, ZnSe and polyphenylenevinylene (PPV). The numerical results obtained are consistent with the literature values and show that the Z-scan technique can be used for characterizing samples of different varieties...[ Read more ]

Nonlinear materials with large optical nonlinearities and fast response speed are required for future photonic devices. In our research, we used a simple and sensitive method named Z-scan (single-beam) technique to measure the optical nonlinearities of liquid, solid and thin-film materials. With the Z-scan technique, both the sign and the magnitude of the nonlinear refractive indices n₂ and the magnitude of the nonlinear absorption coefficients β of a material can be found. In our experiments, we successfully applied the Z-scan technique to determine the nonlinearities of CS₂, CaF₂, ZnSe and polyphenylenevinylene (PPV). The numerical results obtained are consistent with the literature values and show that the Z-scan technique can be used for characterizing samples of different varieties.

We also successfully implemented for the first time, a novel femtosecond time-resolved Z-scan technique to study the mechanism and the relaxation dynamics of optical nonlinearities. In CS₂, we found that molecular Kerr reorientation is responsible for the optical nonlinearities with a relaxation time constant of few picoseconds. In CaF₂, the dominant nonlinearities contribution is from bound-electronic motion with a response time a couple hundred femtoseconds which is the temporal resolution limit of our system. In ZnSe, at low excitation intensity in which two photon absorption is small, positive n₂ due to bound-electronic contribution is observed. At high excitation, two photon generated free-carriers caused a negative n₂. In this free carrier contribution, we have measured two relaxation components with time constants of few picoseconds and few hundred picoseconds. In addition, thermal contribution to n₂ with a relaxation time constant of a few nanoseconds was also observed.