Photoreflectance imaging of a quasi one-dimensional “thermal wave”

We propose a simple configuration to obtain images of the diffusion of a quasi 1-dimensional “thermal wave” in homogeneous or heterogeneous media. One side of the sample is broadly heated by a modulated CO$_2$ laser beam, while the alternative temperature distribution is imaged on a perpendicular facet using a CCD-based thermoreflectance microscope. We validate the principle of this technique on a simple aluminium-coated glass substrate, in which amplitude and phase images of the reflectivity variations are measured. From these measurements, we derive a diffusivity of 10$^{-2}$ cm$^{-2}$s$^{-1}$, which is close to that of glass. This measurement geometry should prove useful for the characterization of complex media in which micro scale heat diffusion is difficult to measure and model