Coherent acoustic phonons emission in copper driven by super-diffusive hot electrons

TL;DR

This paper demonstrates that ultrafast hot electrons in copper can transport energy over hundreds of nanometers and generate coherent acoustic phonons, revealing a new mechanism of energy transfer in metals.

Contribution

It provides experimental evidence that super-diffusive hot electrons can induce coherent acoustic phonons deep beneath the surface of copper at room temperature.

Findings

Hot electrons transport energy over 220nm in copper.

Energy transfer from hot electrons to phonons is demonstrated.

Coherent acoustic phonons are generated deep inside the metal.

Abstract

Ultrafast laser excited hot electrons can transport energy supersonically far from the region where they are initially produced. We show that this ultrafast energy transport is responsible of the emission of coherent acoustic phonons deeply beneath the free surface of a copper metal sample. In particular we demonstrate that enough energy carried by these hot electrons over a distance as large as 220nm at room temperature in copper can be converted into coherent acoustic phonons. In order to demonstrate this effect, several configurations of time-resolved optical experiments of time of flight of coherent acoustic phonons and of hot electrons have been performed.