# Anisotropic ultrafast optical response of terahertz pumped graphene

## TL;DR

This study investigates the ultrafast anisotropic optical response of highly doped graphene to terahertz pulses, revealing nonlinear behavior and developing a theoretical model to explain the underlying electronic dynamics.

## Contribution

The paper provides the first detailed measurement of graphene's anisotropic optical response to terahertz excitation and introduces a comprehensive theoretical model accounting for phonons and electronic momentum displacement.

## Key findings

- Anisotropic response correlates with terahertz electric field modulus.
- Response amplitude increases with carrier density.
- Theoretical model successfully explains the observed anisotropy.

## Abstract

We have measured the ultrafast anisotropic optical response of highly doped graphene to an intense single cycle terahertz pulse. The time profile of the terahertz-induced anisotropy signal at 800 nm has minima and maxima repeating those of the pump terahertz electric field modulus. It grows with increasing carrier density and demonstrates a specific nonlinear dependence on the electric field strength. To describe the signal, we have developed a theoretical model that is based on the energy and momentum balance equations and takes into account optical phonons of graphene and substrate. According to the theory, the anisotropic response is caused by the displacement of the electronic momentum distribution from zero momentum induced by the pump electric field in combination with polarization dependence of the matrix elements of interband optical transitions.