Advanced Plasmonic Photoconductive Sources for Pulsed and Continuous-wave Terahertz Generation.

Optics;Nanophotonics;Terahertz;Plasmonics;Electrical Engineering;Engineering;Electrical Engineering

Yang, Shang-HuaGalvanauskas, Almantas ;

University of Michigan

关键词: Optics;    Nanophotonics;    Terahertz;    Plasmonics;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/133245/shanghua_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Terahertz technology has attracted extensive attention because of its unique applications in environmental monitoring, space explorations, chemical identification, material characterization, security screening, medical imaging, and biological sensing. In the meantime, the practical feasibility of many terahertz systems is still limited by the low power, low efficiency, and bulky nature of existing terahertz sources. Among various techniques for terahertz generation, photoconduction has demonstrated very promising performance for generating both pulsed and continuous-wave (CW) terahertz radiation. Compared to other optically driven terahertz emitters based on nonlinear optical processes, performance of photoconductive terahertz emitters is not constrained by the Manley–Rowe limit and, therefore, can offer significantly higher optical-to-terahertz conversion efficiencies. In spite of their great promise, the performance of existing photoconductive terahertz emitters is severely limited by poor quantum efficiency of ultrafast photoconductors. This limitation is mainly caused by inefficient collection of the majority of the photocarriers in a sub-picosecond time scale. To address this limitation, we introduce novel photoconductive terahertz source designs that incorporate plasmonic contact electrodes to offer significantly higher efficiencies compared to conventional designs. By utilizing plasmonic contact electrodes, a large portion of the incident optical pump beam is concentrated and absorbed in close proximity to the plasmonic contact electrodes. Therefore, the average transport path length of photo-generated carriers to the contact electrodes is greatly reduced. As a result, higher photocurrent levels are fed to the terahertz antenna within the oscillation cycle of the terahertz radiation and higher optical-to-terahertz conversion efficiencies are achieved. We demonstrate record-high optical-to-terahertz conversion efficiencies as high as 7.5%, exhibiting three orders of magnitude higher efficiencies compared to conventional designs. We also demonstrate CW terahertz generation with a radiation frequency tuning range of more than 2 THz and a radiation power of 17 μW at 1 THz, exhibiting a 3-fold higher radiation power level compared to the state-of-the art. Moreover, we demonstrate an integrated photoconductive terahertz source with compact optical pump sources, which offers a very promising solution for future high-performance and compact terahertz imaging and sensing systems.