Jinchi Sun and David G. Cahill
NSF MRSEC Grant no. DMR-1720633
Time-domain thermoreflectance and frequency-domain thermoreflectance (FDTR) have been widely used for non contact measurement of anisotropic thermal conductivity of materials with high spatial resolution. However, the requirement of a high thermoreflectance coefficient restricts the choice of metal coating and laser wavelength. We are developing an alternative frequency-domain pump-probe technique based on probe beam deflection. The beam deflection is primarily caused by thermoelastic deformation of the sample surface, with a magnitude determined by the thermal expansion coefficient of the bulk material to measure. We derive analytical solutions to the coupled elasticity and heat diffusion equations for periodic heating of various geometries of a multilayer sample with anisotropic elastic constants, thermal conductivity, and thermal expansion coefficients.