Resolving Thermal Conductivity Spectrums through Time-resolved Spatial-Temporal Imaging

With the advent of nano-engineered and 2D materials, quasiballistic and anisotropic effects have become more commonplace in thermal properties of these material systems. However, current methods to measure these properties through thermal conductivity generally requires variation of spatial or temporal parameters, or measurement of multiple samples with tedious fabrication procedures. Here, we numerically propose an optical pump-probe technique that uses time-resolved spatial and temporal temperature profile to characterize both quasiballistic and anisotropic thermal transport with no variation of experimental parameters. By performing heat-flow analysis of the thermal profile with multi-parameter optimization, we are able to obtain the thermal conductivity spectrums of both the in-plane and cross-plane heat transport as a function of temporal and spatial frequencies, respectively. Such spectrums can then be used to derive the anisotropy in thermal conductivity and the phonon mean-free-path spectrums within a single experiment. We believe that this technique can enable high throughput screening of thermal properties for nano-engineered and 2D materials.