An experiment for measuring the thermal diffusivity of a liquid sample and nanoparticle colloidal systems using the thermal lens effect, induced by a frequency modulated laser diode, is proposed. The method consists in measuring the photothermal signal depending on the modulation frequency of the laser. From the experimental data is possible to estimate the thermal diffusivity of the sample if the radius of the laser beam is known. The experiment is calibrated by estimating the thermal diffusivity of ethanol. Thermal diffusivity coefficients of aqueous solutions of Brilliant Blue FCF and silver nanoparticles systems are also estimated indicating an increment of an order of magnitude of the nanoparticles system relative to the base liquid. The results show that the method is robust, with a reduced implementation cost and sensitivity enough to thermally characterize transparent and semi-transparent liquid materials.