Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation

TL;DR

This study investigates electronic relaxation in diamond under high-order harmonic femtosecond irradiation, revealing a plasmon-mediated relaxation process in an insulator, supported by experimental UPS spectra and ab initio calculations.

Contribution

First observation of plasmon-mediated electronic relaxation in an insulator, combining experimental UPS data with theoretical calculations.

Findings

Electronic lifetime drops at plasmon energy.

Enhanced low-energy secondary electron production.

Evidence of plasmon excitation in diamond.

Abstract

We used high order harmonics of a femtosecond titanium-doped sapphire system (pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS) measurements on diamond. The UPS spectra were measured for harmonics in the range 13 to 27. We also made ab initio calculations of the electronic lifetime of conduction electrons in the energy range produced in the UPS experiment. Such calculations show that the lifetime suddenly diminishes when the conduction electron energy reaches the plasmon energy, whereas the UPS spectra show evidence in this range of a strong relaxation mechanism with an increased production of low energy secondary electrons. We propose that in this case the electronic relaxation proceeds in two steps : excitation of a plasmon by the high energy electron, the latter decaying into individual electron-hole pairs, as in the case of metals. This process is observed for the first time in an insulator and, on account of its high efficiency, should be introduced in the models of laser breakdown under high intensity.