  The thermal dynamics induced by ultrashort laser pulses in nanoscale systems,
i.e. all-optical time-resolved nanocalorimetry is theoretically investigated
from 300 to 1.5 K. We report ab-initio calculations describing the temperature
dependence of the electron-phonon interactions for Cu nanodisks supported on
Si. The electrons and phonons temperatures are found to decouple on the ns time
scale at 10 K, which is two orders of magnitude in excess with respect to that
found for standard low-temperature transport experiments. By accounting for the
physics behind our results we suggest an alternative route for overhauling the
present knowledge of the electron-phonon decoupling mechanism in nanoscale
systems by replacing the mK temperature requirements of conventional
experiments with experiments in the time-domain.
