In this experimental study, the thermal lens (TL) performance of rhodamine 6G and rhodamine B at different concentrations were investigated using pump/probe laser thermal lens spectroscopy (LTLS). At fixed Nd:YAG laser energy, the TL creation and relaxation times were measured for these compounds. Then, the thermal diffusivity of these materials in various concentrations was obtained at 298 K. Results show that a decrease in the concentration of rhodamine solutions leads to a decrease in the scattering of thermal waves, and an increase in their thermal diffusivities and mobilities. This increase was greater for rhodamine 6G compared to rhodamine B. For pure state (solvent only), the thermo-optical properties were measured experimentally. The results were in complete agreement with the reference values. In addition, to study TL trend, TL signal for both TL creation and relaxation processes was illustrated for concentrations of 10, 50, 100, and 500 ppm.
