In order to characterize low absorbing materials, where UV-vis spectrophotometry does not provide enough sensitivity, other more sensitive methods are needed. Photothermal lens technique is a very sensitive method to detect the material and to characterize it photothermally. The thermal lens technique measures the amount of heat generated followed by the absorption of light in a sample. The heat produces a temperature gradient in the medium which generates a spatial refractive index gradient called a thermal lens. The performance of this method and applications such as photocatalytical degradation of dyes as well as the photothermal characterization of plasmonic nanostructures, quantum dots and graphene are presented.