Decoding the ultrafast formation of a Fermi-Dirac distributed electron gas

TL;DR

This study uses ultrafast spectroscopy to observe the rapid evolution of electron distributions in graphite, revealing complex interactions and timescales involved in forming a thermal Fermi-Dirac electron gas after laser excitation.

Contribution

It provides the first detailed real-time observation of the ultrafast transition from non-thermal to thermal electron distributions in graphite.

Findings

Electron gas reaches Fermi-Dirac distribution within 50 fs.

Different energy and momentum exchange processes occur on distinct timescales.

The transition involves complex interactions among photonic, electronic, and phononic degrees of freedom.

Abstract

Time- and angle-resolved photoelectron spectroscopy with 13 fs temporal resolution is used to follow the different stages in the formation of a Fermi-Dirac distributed electron gas in graphite after absorption of an intense 7 fs laser pulse. Within the first 50 fs after excitation a sequence of time frames is resolved which are characterized by different energy and momentum exchange processes among the involved photonic, electronic, and phononic degrees of freedom. The results reveal experimentally the complexity of the transition from a nascent non-thermal towards a thermal electron distribution due to the different timescales associated with the involved interaction processes.