Indirect multiphoton scattering between light and bulk plasmons via ultrafast free electrons

TL;DR

This paper demonstrates that ultrafast free electrons can coherently mediate interactions between light and bulk plasmons at the nanoscale, enabling new control over plasmon excitations beyond traditional nanoplasmonics.

Contribution

The study introduces a novel method using ultrafast electrons as quantum intermediaries to indirectly couple light with bulk plasmons, revealing new pathways for light-matter interaction.

Findings

Electron energy-loss spectroscopy captures indirect light-BP interactions.

Spectral modulations reveal quantum interference pathways.

Ultrafast electrons enable control of bulk plasmon excitations.

Abstract

Efficient coupling between light and bulk plasmons (BPs) remains a central challenge because of their inherent mode mismatch, limited penetration depth, and pronounced resonant energy mismatch between visible-range photons and BPs. In this work, we demonstrate that ultrafast free electrons can coherently mediate an interaction between electromagnetic fields and BPs at the nanoscale. An electron pulse emitted from the photocathode of ultrafast transmission electron microscope, functions as a quantum intermediary that is capable of simultaneously interacting with the laser field by multiphoton processes and BPs by perturbative scattering. Electron energy-loss spectroscopy can capture this indirect interaction, the final electron energy distribution encodes both quantum pathways arising from distinct combinations of multiphoton absorption and emission and BP scattering events. Interference among these pathways gives rise to characteristic spectral modulations, directly revealing the exchange of energy and information between photons and BPs via the electron delivery. Our results show that femtosecond-driven, ultrafast electrons provide a viable route to modulate and even control bulk plasmon excitations in a volume, thereby extending beyond the conventional nanoplasmonics schemes on manipulating surface plasmons by light. This indirect light-BP interaction paves the promising way for exploring fundamental light-matter interaction at ultrafast and nanometer scales.