Measurement of Temperature Change in Nonlinear Optical Materials by Using the Z-Scan Technique

Spatial and temporal changes of temperature in a novel polymer are investigated by using the Z−scan technique under ns laser pulse excitation. According to the open aperture 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 in temperature are obtained. This change in temperature drives the photo-acoustic and electromagnetic wave propagating in the polymer and induces the change in refractive index, which serves as a negative lens, and the closed aperture Z−scan shows a peak and valley profile. Based on the numerical calculation, we achieve a good fit to the closed-aperture Z−scan curve with an optimized nonlinear refractive index. This consistency attests the existence of temperature change in the solution, and the Z-scan technique is suitable to investigate this change in temperature.