Significant efficiency enhancement in photoconductive terahertz emitters through three-dimensional light confinement

We present a novel photoconductive terahertz emitter, which offers significantly high terahertz radiation power levels through three-dimensional light confinement near terahertz radiating elements. Arrays of plasmonic nano-antennas fabricated on a photo-absorbing semiconductor substrate are used as the terahertz radiating elements. The plasmonic nano-antenna arrays are designed to offer high radiation resistance over a broad terahertz frequency range. An optical reflector layer is embedded inside the substrate to spatially confine and absorb a major portion of an incident optical pump beam near the plasmonic nano-antennas. Therefore, very efficient ultrafast photocurrent can be generated and coupled to the plasmonic nano-antennas for high-efficiency terahertz radiation generation. We experimentally demonstrate record-high terahertz radiation powers as high as 11.4 mW over 0.1-5 THz frequency range with 2.3% optical-to-terahertz conversion efficiency.