Abstract
Photocarrier injection by a femtosecond laser excitation immediately turns off the plasmon resonance in nanoantenna-patterned GaAs, while a strong and short terahertz pulse instantly revives the antenna resonance. The terahertz induced transparency, hugely boosted by the field enhancement in the antennas via the plasmon resonance, exhibits extremely nonlinear effects. The strong terahertz fields drive intervalley scattering and interband tunneling of the photocarriers and consequently reduce the transient conductivity of the photoexcited GaAs leading to the revival of the antenna resonance. In the high-field regime, the transient conductivity rapidly decays in the first few tens of picoseconds after the photoexcitation, while the photocarriers, initially in the highly nonequilibrium state, cool down and reach equilibrium, yet the decay significantly slows down at longer pump delays when the carriers settle down near the bottom of the conduction band.
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