Enhancement of electron hot spot relaxation in photoexcited plasmonic structures by thermal diffusion

TL;DR

This study shows that in confined plasmonic structures, electron thermal diffusion can lead to ultrafast relaxation of hot spots, surpassing lattice energy transfer, and can be controlled by structural and optical parameters.

Contribution

It demonstrates that electron thermal diffusion enables faster hot spot relaxation in plasmonic structures than lattice transfer, with tunable optical responses based on geometry and light properties.

Findings

Sub-picosecond relaxation times observed

Two-temperature model accurately describes relaxation

Optical response can be tuned via structure and light parameters

Abstract

We demonstrate that in confined plasmonic metal structures subject to ultra-fast laser excitation electron thermal diffusion can provide relaxation faster than the energy transfer to the lattice. This relaxation occurs due to excitation of nanometer-sized hot spots in the confined structure and the sensitivity of its optical parameters to the perturbation in these regions. Both factors become essential when the plasmonic resonance condition is met for both excitation and detection. A pump-probe experiment on plasmonic gold lattices shows sub-picosecond relaxation with the characteristic times well-described by a two-temperature model. The results suggest that dynamical optical response in plasmonic structures can be tuned by selection of the structural geometry as well as the choice of wavelength and polarization of the excitation and detection light.