Reflective thermal lensing and optical measurement of thermal diffusivity in liquids

Using a pump-probe laser technique, we analyze the relaxation dynamics of a thermal lens generated at the surface of metal films deposited on a glass substrate. When the film is in contact with a liquid and the film is periodically heated with an optical source, the dynamics of the thermal lens is found to be closely related to the thermal properties of its environment. As a result, reflective thermal lensing can be used to measure the thermal diffusivity of a variety of liquids placed in contact with the film to an accuracy better than 2%. Experimental results point to applications to the study of transient effects in fluids and immiscible liquids, and detection of trace of contaminants in solvents.