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

Abstract

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 101–102 and 102–103 times higher, respectively, for the plasmonic PCA. The highest THz power enhancement of 3×103 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.