Carrier dynamics in graphene studied by ultra-broadband THz time-domain spectroscopy

Carrier dynamics in a single-layered graphene has been studied by ultrabroadband terahertz time domain ellipsometric spectroscopy and time resolved optical pump THz probe technique. We successfully observed the frequency-dependent sheet conductivity of the optically-pumped graphene with and without the photo excitation. Above the optical fluence of 200 μJ/cm², the negative conductivity indicating the possibility of THz wave amplification are realized.