Abstract: A single-beam optical apparatus suitable for measuring thermal diffusivity of a sample having a laser source generating a focused laser beam capable of heating a portion of the sample so as to create a thermal bump via thermal dilation, the thermal bump reflecting a reflected portion of the focused laser beam, means for modulating the intensity of the laser beam, an aperture, a sensor positioned relative to the reflected portion of the focused laser beam so as to generate a measured signal from the reflected portion of the focused laser beam that passes through the aperture, and a module for determining at least the parameters of a relationship between a property of the thermal bump and the measured signal.