Photoluminescence from metal nanostructures following intense ultrashort
illumination is a fundamental aspect of light-matter interactions.
Surprisingly, many of its basic characteristics are under ongoing debate. Here,
we resolve the majority of these debates by providing the most complete
theoretical framework to date that describes this phenomenon, and support it by
experimental confirmation. Specifically, we identify aspects of the emission
that are characteristic to either non-thermal or thermal emission, in
particular, differences in the spectral and electric field-dependence of these
two contributions to the emission. Overall, non-thermal emission is
characteristic of the early stages of light emission, while the later stages
show thermal characteristics. The former dominate only for moderately high
illumination intensities for which the electron temperature reached after
thermalization is close to room temperature. The theory is then complemented by
experimental evidence that demonstrates the novel aspects of our
considerations
