This work presents a new thermal diffusivity measurement technique for thin films as well as bulk materials. In this technique, a modulated laser beam is focused through a transparent substrate onto the film-substrate interface. The generated thermal wave is detected using a fast responding thermocouple formed between the sample surface and the tip of a sharp probe. By scanning the laser beam around the thermocouple, the amplitude and phase distributions of the thermal wave are obtained with micrometer resolution. Thermal diffusivity of the film is determined by fitting the obtained phase signal with a three dimensional heat conduction model. Experimental results are presented for a 150 nm gold film evaporated on a glass substrate.