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Relaxation dynamics of embedded metal nanoparticles after ultrafast laserpulse excitation is driven by thermal phenomena of different origins theaccurate description of which is crucial for interpreting experimental results:hot electron gas generation, electron-phonon coupling, heat transfer to theparticle environment and heat propagation in the latter. Regardingthis lastmechanism, it is well known that heat transport in nanoscale structures and/orat ultrashort timescales may deviate from the predictions of the Fourier law.In these cases heat transport may rather be described by the Boltzmanntransport equation. We present a numerical model allowing us to determine theelectron and lattice temperature dynamics in a spherical gold nanoparticle coreunder subpicosecond pulsed excitation, as well as that of the surrounding shelldielectric medium. For this, we have used the electron-phonon coupling equationin the particle with a source term linked with the laser pulse absorption, andthe ballistic-diffusive equations for heat conduction in the host medium.Either thermalizing or adiabatic boundary conditions have been considered atthe shell external surface. Our results show that the heat transfer rate fromthe particle to the matrix can be significantly smaller than the prediction ofFourier's law. Consequently, the particle temperature rise is larger and itscooling dynamics might be slower than that obtained by using Fourier's law.This difference is attributed to the nonlocal and nonequilibrium heatconduction in the vicinity of the core nanoparticle. These results are expectedto be of great importance for analyzing pump-probe experiments performed onsingle nanoparticles or nanocomposite media.

Non-Fourier heat transport in metal-dielectric core-shell nanoparticles under ultrafast laser pulse excitation