Photo-generated THz antennas: All-optical control of plasmonic materials

Localized surface plasmon polaritons in conducting structures give rise to enhancements of electromagnetic local fields and extinction efficiencies. Resonant conducting structures are conventionally fabricated with a fixed geometry that determines their plasmonic response. Here, we challenge this conventional approach by demonstrating the photo-generation of plasmonic materials (THz plasmonic antennas) on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the definition of different plasmonic antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for an all-optical spatial and temporal control of resonances on plasmonic surfaces and the concomitant control of THz extinction and local field enhancements.