Zhanghua Han, Yangjian Cai, Uriel Levy, Sergey I Bozhevolnyi
https://pubs.acs.org/doi/abs/10.1021/acsphotonics.9b00322
Most terahertz sources nowadays are still inefficient and have low output powers, especially for the continuous-wave THz radiations in the 1~2 THz band, impeding the further development of terahertz science and its applications in various fields. While considerable research effort has been made on the improvement of conversion efficiency from optical/electrical energy to terahertz radiations, less effort is made to maximize the extraction of terahertz energy from the chip to the far field. In this paper, we show a scheme that these two goals can be met simultaneously by making use of multi-spectral resonators, which resonate both in the terahertz band to improve terahertz extraction via Purcell effect and in the optical frequencies exhibiting huge local field enhancement to improve the optical-to-terahertz conversion. Using the nonlinear process of difference frequency generation as an example, our results show that combing a large split-ring resonator (SRR) as a terahertz resonator and nanoscale bowtie optical antennas embedded in the SRR slit, an overall enhancement factor larger than 2×105 in the radiated terahertz power to the free space can be achieved compared to the case when the metallic structures are absent. This scheme of multi-spectral resonators can be extended to other terahertz sources, like the photoconductive antennas, and help realize more efficient terahertz sources.
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