Nonlinear THz Conductivity Dynamics in CVD-Grown Graphene
  We report strong THz-induced transparency in CVD-grown graphene where 92%-96% of the peak-field is transmitted compared to 74% at lower field strength. Time-resolved THz-pump/THz-probe studies reveal that the absorption recovers in 2-3 ps. The induced transparency is believed to arise from nonlinear pumping of carriers in graphene which suppresses the mobility and consequently the conductivity in a spectral region where the light-matter interaction is particularly strong. 
Harold Y. Hwang, Nathaniel C. Brandt, Hootan Farhat, Allen L. Hsu,   Jing Kong, and Keith A. Nelson
cond-mat.mtrl-sci