Raman spectroscopy of graphene under ultrafast laser excitation.15 Feb 2018
The equilibrium optical phonons of graphene are well character-ized 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 Ra-man 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 re-sult 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.