Supersonic strain front driven by a dense electron-hole plasma

TL;DR

This paper investigates how an ultrafast laser-initiated dense electron-hole plasma in germanium generates a coherent, supersonic strain front driven by ambipolar diffusion, with experimental observations supported by detailed simulations.

Contribution

It demonstrates the generation of a supersonic strain front in germanium driven by electron-hole plasma diffusion, supported by combined experimental and simulation analysis.

Findings

Observation of supersonic strain front propagation

Agreement between experimental data and simulations including electron-phonon coupling

Identification of ambipolar diffusion as the driving mechanism

Abstract

We study coherent strain in (001) Ge generated by an ultrafast laser-initiated high density electron-hole plasma. The resultant coherent pulse is probed by time-resolved x-ray diffraction through changes in the anomalous transmission. The acoustic pulse front is driven by ambipolar diffusion of the electron-hole plasma and propagates into the crystal at supersonic speeds. Simulations of the strain including electron-phonon coupling, modified by carrier diffusion and Auger recombination, are in good agreement with the observed dynamics.