Investigation On Transient Thermally Induced Nonlinear Refraction In Metal Cluster Polymer [Tp~*W(μ3-S)3Cu3Py3(μ3-Br)](PF6)/DMF Solution Using The Phase Object Z-scan Technique

As one of the first discussed nonlinear optical mechanisms, thermal effect is always existent when the laser pulses propagate through nonlinear optical materials. The transient thermal nonlinearities have been repaid great attention since appearance of the nanosecond laser pulse. Meanwhile, it also has potential applications in optical limiters. In this paper, we adopt the phase object Z-scan technique to analyze transient thermal effect in liquids based on the 4f coherent imaging technique.This paper introduces the conventional Z-scan method, and according to the basic theory of thermal-induced nonlinearities we obtain the transient thermally induced nonlinear refraction by numerically simulating photo-acoustic equation and the diffusion equation of conduction of heat using the Crank-Nicholson finite difference in transient process. We discuss the self-defocus phenomenon of the thermal refraction which is divided into three parts by the relation of the buildup time for thermal nonlinearities, the laser pulse duration and the thermal diffusive time. We also compared transient thermal refraction with the quasi-steady thermal approximation. The influence of the thermal effect on Z-scan curve is simulated by altering such parameters as the laser pulse width, beam radius and pulse energy etc. We study the dynamics of optical Kerr effect and transient thermal effect.In this dissertation, we introduce the PO Z-scan technique through improving the conventional Z-scan method based on the 4f coherent imaging technique. Also the transient thermal effect is theoretically studied under this method which is found that it can distinguish nonlinear optical mechanisms easily. Meanwhile, the transient thermal-induced PO Z-scan curve is analyzed under influence of different ingredients. The nonlinear optical properties of a novel metal cluster polymer solution of [Tp*W(μ3-S)3Cu3Py3(μ3-Br)](PF6)/DMF were investigated by using PO Z-scan technique with the laser pulse width of 8 ns under different input pulse energy. The result shows that the nonlinear refraction of the sample is due to transient thermally induced nonlinear refraction.