Direct Measurement of Out-of-Plane Thermal Conductivity via Transient Depth Thermography

arXiv:2607.13262v1 Announce Type: new Abstract: Accurate measurement of out-of-plane thermal conductivity remains challenging, particularly for multilayer thin-film materials, due to the reliance of existing techniques on indirect, surface-sensitive observables. Here, we introduce transient depth thermography, a non-contact spectroscopic method that directly reconstructs spatiotemporal temperature profiles using time-resolved thermal radiation. By leveraging the wavelength-dependent optical penetration depth, the technique encodes depth information into the emission spectrum, enabling direct access to internal heat transport dynamics. We demonstrate the method on fused silica and MgF2, achieving agreement with established techniques while attaining an uncertainty of 2-5%. In addition, we measure the temperature-dependent thermal conductivity of MgF2 over a broad temperature range. Applicable to both bulk and thin-film systems, transient depth thermography provides a general and accurate framework for thermal characterization of complex materials.