Nanoantenna Enhanced Terahertz Spectroscopy: Terahertz goes Nano

Improving the sensitivity of terahertz (THz) spectroscopy promises to have a great impact on fundamental and applied studies involving the interaction of such long wavelengths with nanomaterials and molecules at extremely low concentrations. In the past few years, we have shown that THz resonant dipole nanoantennas are effective in confining the radiation on a deep sub-wavelength scale, with a significant field enhancement in close proximity of the nanoantenna ends [1,2]. More recently, we have investigated the end-to-end coupling of THz nanoantennas in chains separated by extremely narrow gaps (down to 20 nm in width). We have found that this configuration enables a giant THz field enhancement (> 1,000) within such gaps. These properties can be used for improving THz sensing on a nano-engineered surface, since the effective absorption of an object scales with the square of the local field. To prove this, we have performed “Nanoantenna Enhanced THz Spectroscopy” (NETS) of a single layer of cadmium selenide quantum dots [3]. We have found that the monolayer’s spectral signature could be detected only when THz nanoantennas were resonantly excited. NETS is based on a distinctive three-dimensional localization of THz radiation on nanoscale dimensions, which allows the ultrasensitive characterization of extremely sub-wavelength objects.