Mechanisms of THz generation from silver nanoparticle and nanohole arrays illuminated by 100 fs pulses of infrared light

Copyright © 2014 American Physical SocietyWe study THz pulses generated from plasmonic metal nanostructures under femtosecond illumination of near-IR light. We find two regimes of excitation, according to the order of the dependence of the THz fluence on the incident near-IR intensity: less then second order at low intensities, changing to approximately fourth order for higher intensities. These regimes are most likely associated with two THz generation mechanisms: optical rectification, and the ponderomotive acceleration of ejected electrons. These data provide evidence that both mechanisms can be at work in the same experiment.Hungarian Scientific Research FundBolyai FellowshipPostdoctoral Fellowship of the Hungarian Academy of SciencesMarie Curie Fellowship of the EU (project acronym `UPNEX'