Schematic of the ultrafast I-V measurement. (a) Oscillating THz probe with controllable peak field E_THz incident from free space, induces the time-dependent current in graphene j = σE_THz, which leads to the attenuation of the THz probe field ΔE _THz due to the conductivity of graphene σ. The Fourier transforms of the THz probes measured before and after the interaction with graphene yield its frequency-dependent conductivity. Thus, the conductivity of graphene is determined for all the frequencies contained in the single-cycle THz probe, the amplitude spectrum (b) of which is covering the operation frequency range of both current and next-generation MOSFETs. The experiment in (a) is repeated for several values of the THz peak field strength in the range 2.3-120 kV/cm, yielding the ultrafast and contact-free I-V characterization of graphene – its frequency- and peak field- dependent conductivity spectrum.