Femtosecond time-resolved dynamical Franz-Keldysh effect

TL;DR

This paper explores the femtosecond-scale dynamical Franz-Keldysh effect, revealing phase shifts in dielectric response under intense laser fields through first-principles simulations and simple models.

Contribution

It introduces a pump-probe formalism combining real-time density functional theory and a two-band model to analyze time-dependent dielectric modulation.

Findings

Time-average modulation aligns with static Franz-Keldysh theory.

A significant phase shift occurs between dielectric response and electric field.

The approach enables femtosecond resolution analysis of optical effects.

Abstract

We theoretically investigate the dynamical Franz-Keldysh effect in femtosecond time resolution, that is, the time-dependent modulation of a dielectric function at around the band gap under an irradiation of an intense laser field. We develop a pump-probe formalism in two distinct approaches: first-principles simulation based on real-time time-dependent density functional theory and analytic consideration of a simple two-band model. We find that, while time-average modulation may be reasonably described by the static Franz-Keldysh theory, a remarkable phase shift is found to appear between the dielectric response and the applied electric field.