| Nonlinear optics mainly focused on two aspects:developing the characterization technique with high sensitivity and reliability; looking for the materials with ultra-fast response time and super optical nonlinearity. The Z-scan technique using scalar light field has been extensively adopted to characterize the optical nonlinearities due to its experimental simplicity, high sensitivity and simultaneous determinations of signs and magnitudes of the optical nonlinearity. However, when the material is imperfect or the nonlinear signal is relatively weak, the sensitivity and reliability of Z-scan measurements will be poor. To improve the sensitivity of the Z-scan technique and to enhance the signal-to-ratio, some improved Z-scan techniques have been developed, mainly concerning change the input beam profiles. As one of the most important basic property of the light field, polarization plays an important role in the interaction of light with matter. By manipulating the distribution of state of polarization of the light field, one can get some special distributions of focal field, such as focal ring, double focal spot, optical needle. These special focal fields will enhance the interaction of light with matter, resulting in numerous novel nonlinear optical effects, which are different from that of the scalar light field. On the other hand, pthalocyanines and porphyrins as the versatile functional pigments with a wide range of applications, pthalocyanines and porphyrins have received extensively attention not only because of their large ?-electron system with two-dimensional conjugate electronic molecular structure, but also because of their exceptional chemical and thermal stability together with versatile functionalization at the peripheral positions and various possibilities of the central meatal ion. The main idea of this thesis is to develop a new nonlinear optical characterization technique and to explore the optical nonlinear properties of novel materials. The main contents of this thesis are as follows:1. We investigated the third-order nonlinear optical properties of both homoleptic substituted phthalocyaninato-rare earth double-decker complexes and donor-?-acceptor A3B type porphyrins using Z-scan technique under the excitation of linear polarized beams in the near infrared region and discussed the physical mechanisms of the observed optical nonlinearity. Firstly, we have confirmed that the homoleptic substituted phthalocyaninato-rare earth double-decker complexes exhibit larger two photon absorption cross-sections due to the expanded delocalized ?-electron system and intense intramolecular ?-? interaction. Secondly, we have demonstrated that due to the donor-?-acceptor structure, both A3B type asymmetric porphyrins 1 and 2 exhibit larger two photon absorption cross sections over the symmetrical because of the intramolecular energy transfer from the excited pyrene moiety to the porphyrin moiety.2. We report the Z-scan technique using vector field for characterizing saturable absorption and third-order refractive nonlinearity. Firstly, we develop the Z-scan technique on a saturable absorber under the excitation of radially polarized beams. As the experimental evidence, we investigate the saturable absorption properties of layered WS2 nanosheets in aqueous suspension by performing the radially polarized-beam Z-scan measurements with femtosecond laser pulse near infrared region. Secondly, we present the Z-scan technique using azimuthal-variant vector beams for characterizing the nonlinear refractive index of an isotropic nonlinear medium. Experimentally, our investigation demonstrates that the Z-scan using radially polarized beams is a preferable technique for characterizing the optical nonlinearity of an imperfect sample. It is shown that the sensitivity and reliability of the Z-scan measurements using radially polarized beams has the great improvement compared with those using the scalar light beams such as Gaussian beams, Laguerre-Gaussian beams, and top-hat beams. |
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