Femtosecond Laser Processing of Germanium: An Ab Initio Molecular Dynamics Study

TL;DR

This study uses ab initio molecular dynamics with density functional theory to simulate femtosecond laser processing of germanium, revealing phase changes and dynamic properties at atomic scale.

Contribution

It introduces a detailed ab initio simulation approach to analyze phase transitions in germanium under femtosecond laser irradiation.

Findings

Germanium undergoes solid, liquid, and gas phase changes under laser irradiation.

The simulation distinguishes irradiated germanium from normal crystal based on melting and dynamics.

Phase transitions are observed within femtosecond laser pulse durations.

Abstract

An ab initio molecular dynamics study of femtosecond laser processing of germanium is presented in this paper. The method based on the finite temperature density functional theory is adopted to probe the structural change, thermal motion of the atoms, dynamic property of the velocity autocorrelation, and the vibrational density of states. Starting from a cubic system at room temperature (300 K) containing 64 germanium atoms with an ordered arrangement of 1.132 nm in each dimension, the femtosecond laser processing is simulated by imposing the Nose Hoover thermostat to the electronic subsystem lasting for ~100 fs and continuing with microcanonical ensemble simulation of ~200 fs. The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find the irradiated germanium distinguishes from the usual germanium crystal by analyzing their melting and dynamic properties.