Investigation Of Optical Nonlinear Dynamics By Pump-Probe 4F Imaging Technique

We use the pump-probe 4F imaging technique combining the Fourier optics and nonlinear optics to study the optical nonlinear dynamics of Kerr liquids, organic macromolecules and semiconductors.We use the Gaussian decomposition method and zeroth-order Hankel transform method to systemically analyze the Z-scan theory. We develop the Z-scan technique appropriate for large nonlinear imaginary phase shift. We study the optical nonlinearities of (t-Bu)₄PcGaI/PMMA film by using nanosecond Z-scan technique under different pulse energies and repetition rates. After eliminating the thermo-optical effect and high-order optical nonlinearities, we determine the third-order nonlinear absorption coefficient and refractive index by Z-scan theory for large absorptive and refractive nonlinearities.Starting with nonlinear wave equation, we use degenerate pump-probe 4F imaging technique to study the two-beam coupling induced by chirped frequency difference in Kerr liquid CS2. We theoretically and experimentally study the case of perpendicular linearly polarized pump and probe beams. We provide the theoretical calculation appropriate for the experimental results. We find the influence of two-beam coupling mechanism in Kerr liquids on the signals of nonlinear dynamic intensity and phase. The experimental results with different polarization states are in good agreement with the theoretical expectation for the stimulated Rayleigh-wing scattering. With the aid of the two-beam coupling theory associated with stimulated Rayleigh-wing scattering, one can determine simultaneously the intensity-dependent nonlinear refractive index, reorientational relaxation time of the molecule and the linear chirp coefficient of laser source.Under the excitation of 532 nm picosecond pulses, we use pump-probe 4F imaging technique to study the optical nonlinear dynamics of ZnPcBr₄/DMSO solution and realize the direct measurement for nonlinear refraction. This new technique can offer not only the high sensitivity but also the simultaneous measurements of excited-state absorptive and refractive nonlinear dynamics. Upon the probe beam propagates within the phthalocyanine solution and interacts with the intense pump beam, we measure the transmitted intensity and phase shift. We make use of the molecular energy-level model to explain the experimental results. With the additional nanosecond open aperture Z-scan measurement, we can unambiguously obtain the photophysical parameters for the energy-level model. We also determine the intensity-dependent refractive index of pure DMSO, shown as a positive and small value. In addition, we measure the contributions of the excited singlet state and lowest excited triplet state to the nonlinear refractive index. We find in ZnPcBr4/DMSO molecular system the two-photon absorption can be neglected, however, the absorption cross sections of the excited states are considerably large compared with that of ground state, and the intersystem crossing time is rather short.We expand the pump-probe 4F imaging technique to the nondegenerate field, and use the nondegenerate conduction-valence band theory systematically analyze the optical nonlinear dynamics in semiconductor ZnSe and ZnS. Our results show that the nondegenerate pump-probe 4F imaging technique can be used to determine the ultrafast bound electronic nonlinearities (such as the multi-photon absorption and intensity-dependent refraction) as well as the cumulative free-carrier nonlinearities (including the absorption cross sections, refractive volumes and the lifetime of carrier) in semiconductors.