Intraband Ultrafast Terahertz Conductivity Dynamics in Graphene

The cooling mechanism is crucial for nanoelectronics, which determines the response time limited for the devices. The cooling process after optical pump in graphene, which is a well-known material with ultrahigh carrier mobility, is therefore an urgent research topic. Ultrafast thermalization and relaxation process in a monolayer graphene film grown on a quartz substrate is investigated by femtosecond laser pump, terahertz probe technique. A typical photo induced negative terahertz conductivity is found, and the electron-phonon-impurity supercollision process is determined to about 2.8 picosecond at different pump photon energy and pump fluence. The competition between the impurity supercollision and the interband-intraband scattering in graphene could give new insight into the design of the application of graphene photonic devices.