Novel Terahertz Sources in the Form of Multispectral Resonators Boosted by Both Pump Light Local Field Enhancement and Terahertz Purcell Effect

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 application 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 multispectral 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 multispectral resonators can be extended to other terahertz sources, like the photoconductive antennas, and help realize more efficient terahertz sources.