The Two-photon Optical Nonlinearities Of Zinc Selenide And Fluorenyl-based Chromophores

Two-photon optical nonlinearity, a multiphoton mechanism in nonlinear optics, is under considerable interest for applications such as optical power limiting, three-dimensional optical data storage, three-dimensional microfabrication, two- photon fluorescence imaging, two-photon frequency-upconverted lasing, and photon- dynamic therapies because of its unique mechanism. The study of two-photon optical nonlinearity is not only helpful to understand the mechanism deeply, but also could supply theoretical support for the development of two-photon nonlinear optical materials. In this dissertation, we study on two-photon optical nonlinearity of different nonlinear materials in theory and experiment. The main research works are listed below:Using the double 4f coherent imaging system, we investigated the two-photon optical nonlinearity of zinc selenide in the near infrared region. Because of using double 4f coherent system, we can measure the optical nonlinearities of materials for laser pulse under poor conditions. This technique is still powerful for laser source with unstable beam output in optical nonlinearity research, which means we can investigate the opticla nonlinearities of materials in broad band. Based on the optical nonlinear mechanism in semiconductors, the nonlinear refraction of free-carrier induced by two-photon absorption is adpoted to interpret the signs change of nonlinear refraction in zinc selenide at the wavelength of 800 nm in picosecond time region.Both two-photon absorption and degenerate two-beam coupling in two Kerr liquids DMF and DMSO have been investigated by time-resolved pump-probe technique. The energy transfer occured in Kerr liquids are interpreted well by the theory of two-beam coupling. Through introducing the two-photon absorption mechanism in the theory of degenerate two-beam coupling, we explain the nonsymmetry of the peak and the valley in the pump-probe experimental resutls well. By analyzing the nonlinear optical parameters obtained by numerical simulating, we concluded the relationship of restoration time between DMF and DMSO.Employing several optical nonlinearity measurements, we characterized the two-photon optical nonlinearities of two novel fluorenyl-based chromophores. Using pump-probe technique, we conclude that the mechanisms of the two novel chromophores is two-photon absorption induced excited state absorption. With the aid of Z-scan technique, we obtain the nonlinear optical parameters related with the three-energy level model. We explain the time-resolved pump-probe experimental results well by the competition between two-beam coupling and two-photon absorption induced excited state absorption. Moreover, the chromophore, which has large two-photon absorption, has been characterized by the optical power limiting experiment. The result indicated that the molecules having two or more nonlinear mechanisms have good optical power limiting property. By comparing the molecule structures and two-photon absorption cross sections of the two new chromophores, the relationship between molecule structure and property is obtained in quality, which is significant for molecule design.By analyzing and comparing the advantages and the lack of two reflection methods for two-photon optical nonlinearity measurement, we developped a new method, reflection phase object Z-scan. We proposed a single-shot reflection technique on the basis of phase object, a more efficient method. Using this single-shot technique, the optical nonlinearity of nontransparent thin film CuPC has been investigated.