In this experimental work, the thermal parameters of polymethyl methacrylate/chloroform solution at different concentrations were investigated using laser mode-mismatched thermal lens spectroscopy. For this purpose, first, the thermal lensing parameters of chloroform, propanone and carbon tetrachloride were measured. The measured values were in agreement with the reference values. The maximum deviation of measured values from reference date for these materials was obtained 1.8%, 1.9% and 1.9%, respectively. Then, the thermal lens process for concentrations of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7 and 0.75 g mL polymethyl methacrylate was studied. The results showed that with decreasing concentration, both the creation and relaxation of the thermal lens process occur more rapidly. In addition, for each of these w/v ratios, the thermal diffusivity was measured. It was found that for this polymer, increasing the concentration leads to a decrease in thermal diffusivity. For changes in the concentration of 0.1–0.75 g mL , the thermal diffusivity of polymethyl methacrylate/ chloroform solution changes in the range of 0.75–0.26 m2 s . In fact, an increase in the concentration of polymethyl methacrylate leads to enhanced scattering of thermal waves, and as a result, the thermal diffusivity is reduced.
