Probing ultrafast carrier-carrier scattering dynamics in epitaxial graphene

Saturable absorption of graphene was experimentally and theoretically investigated in femtosecond time regime with the z-scan technique. The initial ultrafast carrier relaxation time was determined to be ∼8(±3) fs. Such ultrafast dynamics is far beyond the time resolution of other ultrafast techniques with typical hundred fs laser pulses. Our results strongly suggest that graphene is an excellent atomic layer saturable absorber.