Cascaded resonance-enhanced photoconductive antenna (CREPA) for THz emission

With the increasing maturity and popularity of commercial terahertz time-domain spectroscopy (THz-TDS) systems, photoconductive antennas (PCAs) have emerged as the most widely used terahertz source, albeit being plagued by relatively low radiation power. This is partly attributed to the inefficiency of transient photocurrent radiation. However, recent research has shown that the energy carried away by modes propagating along the PCA surface is also non-negligible, and there has been a lack of a universal method to effectively harness this wasted terahertz energy. Herein, we cascade two kinds of resonant meta-atoms on the coplanar transmission lines of PCA, efficiently rescattering the surface modes into the far field, achieving a full-bandwidth enhancement of terahertz far-field power with a total energy increase of up to 17.7 times. Our work provides a reproducible and universal approach to fully exploit the potential of PCAs. Even more valuable, this cascaded resonance-enhanced PCA retains the same breakdown thresholds for bias voltage and pump power as conventional PCAs, opening quick access for direct adoption in THz-TDS instruments and advancing the practicality of terahertz techniques.