The measurement accuracy of two methods (based on falling and rising signal regions) for thermal diffusivity measurement was compared. Thermal diffusivity of chloroform, hexane, heptane, acetone, and methanol was measured using these two methods based on thermal lens spectroscopy. Results showed that the average of percentage error for rising signal region method is about six times higher than falling signal region method. Therefore our experimental setup based on falling signal region, with 0.56% error average from literature values, can be used as an ultra-sensitive setup to measure thermal diffusivity. Then, temporal evolution of these liquids for falling and rising signal regions has been studied. Also, thermal lens signal versus Nd:YAG laser energies were investigated. Finally, thermal diffusivity in various laser energies was measured, and result showed that at least for 50–125 mJ laser energy range, thermal diffusivity is almost constant. The agreement between our experimental results and literature values was excellent.
