Significant Radiation Enhancement in Photoconductive Terahertz Emitters   by Incorporating Plasmonic Contact Electrodes
  Even though the terahertz spectrum is well suited for chemical identification, material characterization, biological sensing and medical imaging, practical development of these applications has been hindered by the attributes of terahertz sources, namely low output power and poor efficiency. Here, we demonstrate that use of plasmonic contact electrodes can significantly enhance the optical-to-terahertz conversion efficiency in a photoconductive terahertz emitter. The use of plasmonic contact electrodes offers nanoscale carrier transport path lengths for the photocarriers, enabling efficient collection of the majority of carriers in a sub-picosecond time-scale. It also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. We experimentally demonstrated 50 times higher terahertz radiation power from a plasmonic photoconductive emitter in comparison with a similar photoconductive emitter with non-plasmonic contact electrodes. 
Christopher W. Berry, Mohammad R. Hashemi, Mehmet Unlu, and Mona   Jarrahi
physics.optics