Photoconductive Meta‐Antenna Enabling Terahertz Amplitude Spectrum Manipulation

In recent years, as a promising new method, integrating nanostructures to improve the power of photoconductive antennas has received widespread attention. However, there are few reports on the application of artificial electromagnetic structures to regulate the spectral features of photoconductive antennas. Herein, it is demonstrated that by integrating split-ring resonator (SRR)-like metallic structures onto the coplanar lines of the photoconductive antenna transmitter, one can significantly manipulate the spectral feature of the generated terahertz (THz) radiation. The guided THz wave along the coplanar lines is scattered by the SRRs to the far field and interferes with the THz pulse radiated from the photoconductive antenna gap, leading to enhancement of the photoconductive antenna's energy and modulation in the spectrum. Further studies have shown that the strength, frequency, and band-pass/band-stop characteristics of the modulation can be altered by changing the geometry and placement of the SRRs. Water vapor absorption is also discussed to exemplify the benefit of this novel meta-antenna over the ordinary photoconductive antenna in sensing scenario. The photoconductive antenna proposed here takes the lead in using artificial structures to manipulate the spectral domain behavior of photoconductive antennas, which is of great significance for THz spectroscopy, imaging, and sensing.