OPTICAL MEASUREMENTS OF THERMAL-DIFFUSIVITY OF A MATERIAL

The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the hea t transfer in the solid subjected to a thermal process, to monitor sur face composition or morphology, or to detect invisible subsurface defe cts like delaminations. This measurement can be done in a noncontact m anner using various photothermal methods. Such methods typically invol ve pulsed heating of the surface by small amounts using a laser source ; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various pro bing methods have been developed in the literature, including the prob ing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their ap plications.