Micron-scale measurements of the coefficient of thermal expansion by time-domain probe beam deflection

Abstract

We describe a pump-probe optical technique, time-domain probe-beam deflection, that enables measurements of the coefficient of thermal expansion (CTE) with micron-scale spatial resolution. Our quantitative model for the beam deflection includes contributions from thermal expansion of thin films deposited on a substrate, thermal expansion of the substrate, elastic deformation of the substrate, heating of air above the surface of the sample, and the lateral temperature gradient at the surface of the sample. The usefulness of this technique for high-throughput CTE measurement is demonstrated by two experiments: we are able to find the Invar alloy composition directly from a simple Fe–Ni diffusion couple and we find abnormal CTE increase in an ≈100μm region of dentin adjacent to the dentin-enamel junction of a human tooth. Such a CTE abnormality would be difficult to find using other techniques.