First-principles study of ultrafast and nonlinear optical properties of graphite thin films

TL;DR

This study uses first-principles simulations to explore ultrafast and nonlinear optical behaviors of graphite thin films, revealing phase transitions and saturable absorption effects under strong pulsed electric fields.

Contribution

It provides a detailed theoretical analysis of transient optical responses and light propagation in graphite thin films using time-dependent density functional theory.

Findings

Graphite exhibits a phase transition from conducting to insulating under certain electric field intensities.

Saturable absorption occurs, limiting energy transfer at high field amplitudes.

Optical response shows a sudden change and small attenuation during light propagation.

Abstract

We theoretically investigate ultrafast and nonlinear optical properties of graphite thin films based on first-principles time-dependent density functional theory. We first calculate electron dynamics in a unit cell of graphite under a strong pulsed electric field and explore the transient optical properties of graphite. It is shown that the optical response of graphite shows a sudden change from conducting to insulating phase at a certain intensity range of the applied electric field. It also appears as a saturable absorption, the saturation in the energy transfer from the electric field to electrons. We next investigate a light propagation in graphite thin films by solving coupled dynamics of the electrons and the electromagnetic fields simultaneously. It is observed that the saturable absorption manifests in the propagation with small attenuation in the spatial region where the electric field amplitude is about $4 \sim 7 \times 10^{-2}$ V/Angstrom.