Broadband Terahertz Detection with 100 dB Dynamic Range through a High Switching-Contrast Plasmonic Nanocavity

We present a photoconductive terahertz detector, which offers high-sensitivity and broadband detection performance for terahertz time-domain spectroscopy at record-low optical pump power levels. The detector employs a plasmonic nanocavity designed to confine the optical pump photons in a thin photoconductive region. By providing an efficient optical absorption in this thin layer, the carrier transport time to the device contact electrodes is maintained in a sub-picosecond range for the majority of the photo-generated carriers. Therefore, ultrafast operation and high quantum efficiency is achieved simultaneously, which significantly increases the detector responsivity and dynamic range even at very low optical pump power levels. We experimentally demonstrate a 100 dB dynamic range over a 0.1-6 THz frequency range at only a 0.1 mW optical pump power level.