Investigation of the temperature dynamics process in the nonlinear optical materials by using PO Z-scan technique

The spatial and temporal changes of temperature in a novel polymer are investigated by using PO Z-scan technique under ns laser pulse excitation. The PO Z-scan is a new and high sensitivity laser detection technique. It can be employed to investigate nonlinear optical properties. According to the open aperture PO Z-scan experimental results, the nonlinear absorption coefficient of the polymer is determined. By solving the diffusion equation of heat conduction induced by optical absorption, the spatial and temporal changes of temperature are obtained. This change of temperature drives the photo-acoustic and electromagnetic wave propagating in the polymer and induced the change of density distribution of the sample. The changes in temperature and density induced the variation of refractive index. Based on the numerical calculation, we achieved a good fitting to the closed-aperture PO Z-scan curve with an optimized nonlinear refractive index. This consistency attests the existence of temperature change in the solution and indicates that the PO Z-scan technique is suitable to investigate this change of temperature.