| With the dramatic development of optical fiber communication and the application of dense wavelength division multiplex (DWDM) technique, there are many electronic components with some disadvantages such as slow switching speed, clock displacement, serious crosstalk and high power loss in the present optical-electro and electro-optical convert devices, which need to be solved immediately. All-optical switches (AOS) are among the key apparatuses to solve these disadvantages. The principle of optical switches is taking advantage of the third-order nonlinear optical (NLO) properties of materials. With a control beam inducing the change of refractive index of materials, the other signal beam transmitting in the material will produce an additional phase difference, therefore to realize the function "On" or "Off' of optical switches.Besides, materials with proper third-order nonlinear optical properties can also be used for optical limiting devices. With the super fast laser invention, the optical intensity density of laser can get to hundreds of GW/cm~2. On this condition, naked eyes are easy to get hurt and the detector also easy to damage. The optical limiting (OL) devices mainly use the NLO effects of materials such as reverse saturable absorption and two-photon absorption etc., which can effectively protect the naked eyes and detectors.According to the requirement of AOS, material suitable for them should possess high third-order nonlinear refractive index, low linear absorption and nonlinear absorption. And, OL devices require materials with larger two-photon absorption or saturable absorption coefficient. Therefore, the precise characterization of third-order nonlinear optical properties is significant to explore materials, optimize materials to satisfy the requirement of optical devices. My main work is as follows:Firstly, with exploring materials possessing high third-order NLO properties, we synthesized three novel DMIT salts (BuCu, BuCo and EtCo) through change their central metal ions and positive ion. DMIT salts have theπ-electron delocalization in a conjugated systems and the d-orbit of transition metal contribute to the large third-order nonlinearity and ultrafast response capability together.Secondly, at a wavelength of 1064 nm with laser duration of 40 ps, the open aperture and closed-aperture Z-scan experiment of t BuCu, BuCo and EtCo were studied and their NLO mechanism were analyzed. The Z-scan technique is a simple, sensitive and single-beam method which can determine both the nonlinear refractive index and nonlinear absorption coefficient of a given material. The detailed deduction of Z-scan function and the method to calculate nonlinear refractive index, nonlinear absorption efficient, third-order nonlinear susceptibility and the molecular second hyperpolarizability were given. Z-scan spectra reveal their negative Kerr coefficients at 1064nm and nonlinear absorptions were observed.Thirdly, the EtCo's and BuCu's third-order NLO properties of different concentrations and of different laser intensities were studied. The NLO refraction and absorption properties of BuCu, BuCo and EtCo were compared, the reasons for the difference were discussed, and their potential applications in AOS were evaluated. Under the same light intensity, if the NLO absorption coefficient is proportional to the concentration of the solutions, indicating that the valley and peak in the Z-scan curves originated from the material, not from the solvent or the quartz cuvette. That NLO absorption coefficient is proportional to the input intensity indicates that the third-order NLO properties of the sample originate from optical Kerr effect and thermal effect can be ignored.Our research indicates that changing the central metal ions and positive ion of complexes can optimize the NLO properties of materials, enhance the Q-factor W and reduce the Q-factor T. We believe it is promising to utilize these complexes in AOS through optimizing these complexes.
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