With ever-decreasing device downscaling, understanding thermal transport in nanoscale systems is a key technological issue . In this context, we theoretically address the ultrafast cooling of metal nano-objects embedded in transparent environment as measured in time-resolved optical spectroscopy . In the experiment a “pump” laser pulse impulsively heats a metal nano-object. The thermal relaxation is then accessed exploiting a time-delayed “probe” pulse, monitoring the temperature-dependent relative transmittivity variation. The modeling, based on the Finite-Element Method, couples the two physics involved in the experiment, namely thermal and optical problem. The system thermal dynamics is first computed in the frame of Fourier law and Kapitza-like thermal resistance . The system electromagnetic extinction spectrum is then calculated at various delay times, thus accounting for the temperature-dependent variations of the system dielectric functions. Within this frame we numerically simulate the experiments performed on metal nano-spheres embedded in a liquid environement and metallic nanodisks patterned on a dielectric substrate. By tuning the Kapitza resistance we obtain a good agreement between the experimental and theoretical optical traces, allowing to estimate the Kapitza resistance at metal nano-object-environment interface.
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