Terahertz Photoconductive Emitter With Dielectric-Embedded High-Aspect-Ratio Plasmonic Grating for Operation with Low-Power Optical Pumps

Here we report design, optimization and fabrication of a plasmon-assisted terahertz (THz) photoconductive antenna (PCA) for THz pulse generation at low-power optical pumps. The PCA design combines a high-aspect ratio dielectric-embedded plasmonic Au-grating placed into the photoconductive gap. Antenna structure, Si
₃
N
₄
-passivation of the photoconductor and the Al
₂
O
₃
-antireflection coating are used to further enhance antenna performance. Both the plasmon-assisted and conventional pCAs were fabricated for comparative analysis of their transient photocurrents, THz waveforms and THz power spectra. A superior performance of the plasmon-assisted PCA was confirmed. Thus, depending on the optical pump power, the transient photocurrent and the THz power spectrum were 10
¹
-10
²
and 10
²
-10
³
times higher, respectively, for the plasmonic PCA. The highest THz power enhancement of 3×10
³
was observed at low-power optical pumps of <; 1.0 mW. These results demonstrate a strong potential of the plasmonic PCA for operation with low-power lasers; thus, opening new opportunities for the development of portable and cost-effective THz spectrometers and imaging systems.