Crossover from non-thermal to thermal photoluminescence from metals excited by ultrashort light pulses

TL;DR

This paper presents a comprehensive theoretical and experimental study of photoluminescence in metal nanostructures under ultrashort light pulses, distinguishing non-thermal from thermal emission based on spectral and electric field characteristics.

Contribution

It provides a new theoretical framework that clarifies the transition from non-thermal to thermal photoluminescence in metals, supported by experimental validation.

Findings

Non-thermal emission dominates early stages of light emission.

Thermal emission appears at later stages with higher electron temperatures.

Spectral and electric field dependence differentiate the two emission types.

Abstract

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 many of these debates by providing a comprehensive theoretical framework 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 remains close to room temperature. The theory is complemented by experimental evidence that demonstrates the novel aspects of our considerations.