Abstract: The thermal lens effects based on the strong pulsed laser excitation were observed by using the home-made experimental apparatus. In acetone-water mixture concentrations of CoCl₂as low as 3×10^-7M have been determined with present setup, which corresponds to an absorbance of 6×10^-6. In thermal lens measurements the noise level due to shot-term instability of the He-Ne laser output amplitude can be reduced down by the use of differential amplification technique, thus the S/N ratio is improved appreciably.