▎ 摘　　要

Time-resolved high-field terahertz (THz) spectroscopy of photoexcited graphene demonstrates extraordinary photocarrier dynamics in single-layer graphene. Strong THz fields and photoexcitation simultaneously enhance the THz transmission of graphene mainly due to the increase of carrier scattering rates. A theoretical analysis confirms that the graphene conductivity undergoes transient decreases to the large extent under the THz and optical excitations, indicating that both the strong THz fields and photoexcitation effectively elevate the carrier scattering rates. The relaxation of photocarriers, on the other hand, shows opposite effects of the THz fields and photoexcitation. Photoexcitation increases the relaxation time via the reabsorption of optical phonons by photocarriers, while strong THz fields reduce the relaxation time because the field-induced redistribution of electrons opens up unoccupied states in the conduction band and consequently enhances the relaxation and the phonon emission. (C) 2018 Optical Society of America