Terahertz photoconductive emitter with dielectric-embedded high-aspect-ratio plasmonic grating for operation with low-power optical pumps

Abstract

We report on the design, optimization and fabrication of a plasmon-assisted terahertz (THz) photoconductive antenna (PCA) for THz pulse generation at low-power optical pumps. The PCA features a high aspect ratio dielectric-embedded plasmonic Au grating placed into the photoconductive gap. Additionally, Si 3 N 4 -passivation of the photoconductor and the Al 2 O 3 -antireflection coating are used to further enhance antenna performance. For comparative analysis of the THz photocurrents, THz waveforms and THz power spectra we introduced the THz photocurrent δ i and the THz power enhancement δ THz factors, which are defined as ratios between the THz photocurrents and the THz power spectra for the plasmon-assisted and conventional PCAs. We demonstrated superior performance of the plasmon-assisted PCA δ i =30 and δ THz =3 10 3 at the lowest optical pump power of P=0.1 mW. Nevertheless the increase to P=10 mW lead to monotonically decrease in the both values to δ i =2 and δ THz =10 2 due to screening effects. These results demonstrate a strong potential of the plasmonic PCA for operation with low-power lasers, thus, opening opportunities for the development of portable and cost-effective THz spectrometers and imaging systems.