Study Of Excited State Absorption Enhanced Thermal Effect In Fullerene/Toluene Solution

As one of the first discussed nonlinear optical mechanism thermal nonlinearities is always existent during the laser pulse propagation through nonlinear optical materials. Recently, it has been repaid attention because of its potential applications in optical limiters in nanosecond regime. In this dissertation, we especially study excited state absorption enhanced thermal refraction in fullerene toluene solution which is based on transient thermal induced refraction.The excited state absorption and refraction are discussed for the basic of five-energy-band model, combined photo-acoustic equation and the diffusion equation of conduction of heat, we study the dynamics of excited refraction and excited absorption enhanced thermal refraction, as well as the dynamics of Kerr effect and excited absorption enhanced thermal refraction, and discuss the transformation of self-focus and self-defocus.The nonlinear optical properties of C₆₀/toluene solution are studied by using Z-scan technique with 4ns duration laser pulse at 532nm wavelength, and the experimental results are analyzed by using the theory of excited absorption enhanced thermal refraction. When the energy of the pulse is very low, the nonlinear refraction of C₆₀/toluene solution is mostly coursed about excited refraction, however, when the pulse energy is higher, the excited absorption enhanced thermal effect and Kerr effect must be considered, furthermore, when the pulse energy increase more, nonlinear scattering also play a great role in the nonlinearities of the solution. The study of different laser pulse indicates that the excited absorption enhanced thermal effect and nonlinear scattering are increasing along with the increasing of the width of laser pulse.