# Raman spectroscopy of graphene under ultrafast laser excitation

## TL;DR

This study investigates the non-equilibrium Raman response of graphene under ultrafast laser pulses, revealing how hot charge carriers influence phonon linewidths at high electronic temperatures, relevant for optoelectronic applications.

## Contribution

It provides new insights into the non-equilibrium phonon dynamics in graphene under ultrafast excitation, highlighting the impact of hot carriers on Raman spectral features.

## Key findings

- Raman linewidths increase with electronic temperature
- Hot carriers reach temperatures of 1700-3100K
- Electron-phonon scattering broadens Raman peaks

## Abstract

The equilibrium optical phonons of graphene are well characterized in terms of anharmonicity and electron-phonon interactions, however their non-equilibrium properties in the presence of hot charge carriers are still not fully explored. Here we study the Raman spectrum of graphene under ultrafast laser excitation with 3ps pulses, which trade off between impulsive stimulation and spectral resolution. We localize energy into hot carriers, generating non-equilibrium temperatures in the ~1700-3100K range, far exceeding that of the phonon bath, while simultaneously detecting the Raman response. The linewidth of both G and 2D peaks show an increase as function of the electronic temperature. We explain this as a result of the Dirac cones' broadening and electron-phonon scattering in the highly excited transient regime, important for the emerging field of graphene-based photonics and optoelectronics.