Concentration-dependent nonlinear refraction in tetrasulfonated copper phthalocyanine solution

By using the Gaussian Z-scan technique, a transition from the self-focusing property to the self-defocusing property with a decrease in concentration under 11ns pulse excitation in tetrasulfonated copper phthalocyanine (CuPcTs) dissolved in dimethyl sulfoxide (DMSO) is observed, which is due to the coexistence of excited-state refraction and transient thermal-lens effect. The nonlinear optical properties of a CuPcTs/DMSO solution are investigated by using the top-hat Z-scan technique under different laser pulse excitations with the same fluence at 532nm. The mechanism of the optical nonlinearities for the solution is studied by using an improved picosecond time-resolved pump-probe technique which can simultaneously measure the dynamic nonlinear absorption and refraction conveniently. The experimental results are described very well by using a simple three-level model and the theory of the transient thermal refraction in liquids. The values for the excited-state absorption and refraction cross section are also obtained.