Nonlinear photoluminescence in gold thin films

TL;DR

This study uncovers a new ultrafast electronic heat transport mechanism that governs the nonlinear photoluminescence in gold thin films, highlighting the role of hot electron dynamics and diffusion at nanoscales.

Contribution

It introduces a novel understanding of nonlinear optical response in metallic films driven by ultrafast thermal dynamics and hot carrier diffusion, supported by experimental and first-principles modeling.

Findings

Ultrafast electronic heat transport dominates nonlinear response in thin gold films.

Hot electron and hole distributions significantly influence photoluminescence.

Thermal dynamics and diffusion control the temporal evolution of the nonlinear signal.

Abstract

Promising applications in photonics are driven by the ability to fabricate crystal-quality metal thin films of controlled thickness down to a few nanometers. In particular, these materials exhibit a highly nonlinear response to optical fields owing to the induced ultrafast electron dynamics, which is however poorly understood on such mesoscopic length scales. Here, we reveal a new mechanism that controls the nonlinear optical response of thin metallic films, dominated by ultrafast electronic heat transport when the thickness is sufficiently small. By experimentally and theoretically studying electronic transport in such materials, we explain the observed temporal evolution of photoluminescence in pump-probe measurements that we report for crystalline gold flakes. Incorporating a first-principles description of the electronic band structures, we model electronic transport and find that ultrafast thermal dynamics plays a pivotal role in determining the strength and time-dependent characteristics of the nonlinear photoluminescence signal, which is largely influenced by the distribution of hot electrons and holes, subject to diffusion across the film as well as relaxation to lattice modes. Our findings introduce conceptually novel elements triggering the nonlinear optical response of nanoscale materials while suggesting additional ways to control and leverage hot carrier distributions in metallic films.