ACS Photonics, Just Accepted Manuscript
DOI: 10.1021/ph500251a
Publication Date (Web): October 30, 2014
Copyright © 2014 American Chemical Society
We present measurements of the enhanced emission of terahertz pulses after the optical excitation of grating-coupled near-IR surface plasmons at the interface of gold and cuprous oxide, using femtosecond laser pulses. Terahertz emission is the result of the acceleration of charge carriers optically excited in the Schottky depletion field of the metal/semiconductor interface. The enhancement is a direct consequence of the localized nature of the surface plasmon field which is strongest near the nanostructured metal surface where the Schottky electric field is strongest too. Surface plasmon excitation is confirmed by reflection spectroscopy of gratings with different periods, by varying the azimuthal angle of the grating, and by calculations of the plasmon frequencies and fields. We observe a terahertz field enhancement factor of ~5.8 when compared to the emission from a flat sample. This corresponds to a THz power-enhancement factor of ~34. Our results show that for THz emission from these metal/semiconductor interfaces it matters more where the pump light is absorbed, than how much pump light is absorbed.
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