Real-time ab initio description of the photon-echo mechanisms in extended systems: the case study of bulk GaAs

TL;DR

This study presents an ab initio real-time analysis of photon-echo mechanisms in bulk GaAs, comparing results with a two-level system model, and explores high-field effects relevant for ultrafast laser applications.

Contribution

It introduces a novel ab initio computational approach to analyze photon-echo phenomena in extended systems like GaAs, including high-field effects and multi-band interactions.

Findings

Ab initio results agree with TLS model at low fields.

Differences emerge at high fields due to multi-band effects.

Pulse fluences near π area are below damage threshold.

Abstract

In this paper we present an ab initio real-time analysis of free polarization decay and photon echo in extended systems. As a prototype material, we study bulk GaAs driven by ultra-short laser pulses of 10 fs (energy spread of 0.4 eV), with frequency tuned in the continuum of the optical spectrum. We compute the electronic polarization P(t), and define a computational procedure to extract the echo signal in the dipole approximation. Results are obtained in both the low and high field regime, and compared with a two-levels system (TLS) model, with parameters extracted from the ab initio simulations. ab initio results are in optimal agreement with the TLS in the low-field case, whereas some differences are observed in the high-field regime where the multi-band nature of GaAs becomes relevant. In the high field regime we compute the pulse area, and look for fluences with pulse area close to {\pi}. We highlight that such fluences are well below the damage threshold of GaAs. However a unique value of the area cannot be defined, due to the strong dependence of the transition dipoles in the energy window excited by the laser pulse.